Clinical Imaging xxx (2015) xxx–xxx
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Clinical utility of dual-energy CT for gout diagnosis Hui-Juan Hu, Mei-Yan Liao ⁎, Li-Ying Xu Department of computed tomography, Zhongnan Hospital of Wuhan University, 169 East Lake Road, Wuhan 430071, PR China
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Article history: Received 16 June 2014 Received in revised form 4 December 2014 Accepted 24 December 2014 Available online xxxx Keywords: Gout Dual-energy CT Urate crystal Tophi
a b s t r a c t Objective: The present study was to evaluate the clinical value of dual-energy computed tomography (DECT) for detecting monosodium urate crystals in patients with gouty arthritis. Methods: Two hundred and two patients, who experienced arthrocele and (or) joint pain, were enrolled into our study. DECT scans of upper or lower extremity were performed. One hundred and sixty one patients who conformed to the American College of Rheumatology classification standard were defined as the gout group. The rest (41) of the patients were regarded as the without-gout group. DE (80 kV/140 kV) datasets were reconstructed via DE gout software. Images were reviewed independently by two senior radiologists. Results: In the gout group, DECT scans revealed a total of 379 areas of urate deposition in 121 patients. In the without-gout group, 3 areas of green urate deposition were detected. The sensitivity and specificity were 75.2% and 92.7%, respectively; when we increased the ratio to 1.32 and decreased the range to 3, the number of patients with green urate deposition increased, and the areas of urate deposition were more extensive. The sensitivity and specificity were 91.9% and 85.4%. DECT images could illustrate the palpable reduction in the tissue urate deposits compared to baseline images before and after treatment. Conclusions: DECT has comparable sensitivity and specificity for the detection of gouty arthritis in a clinical setting, and DECT can monitor the clinical treatment. However, DECT results should be interpreted carefully because there could be some false-negative or false-positive findings. © 2014 Published by Elsevier Inc.
1. Introduction Gout is characterized as a metabolic disorder in which there is either an increase in the production of uric acid or a decrease in the excretion of uric acid, resulting in hyperuricemia [1]. Long-lasting hyperuricemia causes deposition of monosodium urate (MSU) crystals in the joints and soft tissues, triggering gouty arthritis and, if not properly treated, the formation of gouty tophi [2]. An increased incidence and prevalence of gout has been reported, it is generally attributed to trends in lifestyles leading to increases in gout risk factors, such as obesity, metabolic syndrome, hypertension and alcohol consumption [3], at least 1% to 2% of all adults in the industrialized nations are now affected by gout [4]. The repeated recurrence of the gouty arthritis can cause deformity and disability, and it is strongly associated with metabolic syndrome, myocardial infarction, insulin resistance, stroke, and premature death, affecting patient’s quality of life and work severely [5–9]. For these reasons, early diagnosis and treatment are very important. Establishing a diagnosis of gout on the basis of clinical and laboratory criteria is generally straightforward. There are several other diseases that can mimic or coexist with gout, including septic arthritis, reactive arthritis, rheumatoid arthritis, osteoarthritis, erosive osteoarthritis, psoriasis, calcium pyrophosphate dihydrate crystal deposition, amyloidosis, pigmented ⁎ Corresponding author. Department of CT, Zhongnan Hospital of Wuhan University, 169 East Lake Road, Hubei, Wuhan, P.R. China. Tel.:+86 18971096590. E-mail addresses: [email protected] (H.-J. Hu), [email protected] (M.-Y. Liao), [email protected] (L.-Y. Xu).
villonodular synovitis, amyloid arthropathy, sarcoidosis, and so on [10,11], which may obscure or delay clinical diagnosis and affect patient treatment. The current common imaging techniques used to confirm and monitor gout include radiography, ultrasound, computed tomography (CT), and magnetic resonance imaging. However, these techniques are not specific enough to facilitate the diagnosis of gout [12]. The presence of MSU crystals would confirm the diagnosis of gout, so the optimal imaging technique should be highly specific for MSU deposition. The advent of dual-energy CT (DECT) has the potential to reach the aim. Dual-source CT scanners are equipped with two X-ray tubes allowing simultaneous acquisition at two different energy levels; thus, it is superior to the present single-energy (single-source) CT because of its ability to extract information and characterize the chemical composition of material according to the differential X-ray photon energydependent attenuation of the compounds being examined at the two different energy levels [10]. Utilizing this ability, DECT has been successfully shown in the literature to confirm the presence of MSU crystals in and around joints in gout arthropathy [13–15]. In this article, we demonstrate the ability of DECT to detect MSU deposition in gouty arthritis patients. 2. Materials and methods 2.1. Patients We retrospectively evaluated the imaging and clinical data of 202 patients who experienced joint swelling and (or) pain between October
http://dx.doi.org/10.1016/j.clinimag.2014.12.015 0899-7071/© 2014 Published by Elsevier Inc.
Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
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2010 and December 2013. Written informed consents were obtained from these patients. All information on patient demographic data, clinical and laboratorial presentation, underlying diseases, imaging manifestations, and pathological findings were recorded. 2.2. DECT examination DECT scans of upper or lower extremity were performed in 398 joints in different anatomical regions, such as the hands and wrists, elbows, knees, ankles, and feet. A 64-row dual-source CT scanner (Somatom Definition; Siemens, Germany) equipped with two X-ray tubes and detectors was used. In upper extremity scans, patients were positioned head first in a prone position. Forearms and wrists were positioned forward of the patient’s head with hands in a neutral position. Palms were placed with the dorsum facing up in a relaxed dorsiflexion position. In lower extremity scans, patients were positioned feet first in a supine position, with the knees bent approximately in a 90° position, with the feet in a firm plantarflexion position. The scan parameters were as follows: tube A: 140 kV, tube B: 80 kV, collimation 64×0.6 mm, pitch 0.7; dual-energy tube current parameters were different according to the scanned anatomical region: tube A reference (ref.) milliampere second (mAs) =40, tube B ref. mAs =170, for hands and wrists, elbows; and tube A ref. mAs=55, tube B ref. mAs=234, for ankles, feet, and knees. All scans were obtained without intravenous contrast agent. Transverse sections were reconstructed from the DE datasets, with a slice thickness of 0.75 mm and with a composition of 0.3 in the soft tissue kernel (D30). 2.3. Postprocessing and interpretation The transverse datasets of both tubes were loaded onto Syngo MultiModality Work-place (Siemens, Forchheim, Germany) and reconstructed with available software program (DE Gout; Siemens, Germany). Then, an image-based two-material decomposition algorithm of the datasets was subsequently performed to separate calcium from MSU, using soft tissue as the baseline (Fig. 1) The material-specific differences in attenuation of the two datasets (80 and 140 kVp) enabled an easy classification of the elementary chemical composition of the scanned tissue, allowing accurate characterization of uric acid (color coded in green) separately from the calcium and bone marrow (cortical bone color coded in blue and medullary bone in pink) [12].
The two-material decomposition algorithm is based on the physical principle that attenuation of photons depends on atomic number and energy of the photons. Material with a high atomic number (e.g., calcium) has a higher change in attenuation than does material with low-atomic-number components (e.g., uric acid). This difference in attenuation directly translates into a difference in CT values. The y-axis represents the attenuation values of the lower-kilovoltage tube (80 kV), and the x-axis represents the attenuation values of the higher-kilovoltage tube (140 kV). Pixels with a higher slope (high atomic number) are plotted above the line and represent calcium; the pixels below the line represent uric acid (lower atomic numbers of its component elements) [12]. 2.4. Image evaluation The base material “soft tissue” was chosen to be at 80 kV (50 HU) and at 140 kV (50HU), ratio 1.25, range 5; the range of values for the calculation was set between 125 and 3,000.The parameter ratio meant the slope of the separation line; we can find more MSU by increasing the ratio. Range meant smooth filter of pixel; it can increase density resolution while missing some detail. Thus, if the patient with clinical suspicion of gout had no MSU crystals, we would increase the ratio to 1.32 and decrease the range to 3 [16]. DECT images were evaluated by two senior radiologists. The readers were blinded to the patients’ clinical data. They read the images independently in the workplace. The readers were asked to classify the examination findings as positive or negative for the presence of MSU crystals, record the places of urate deposition, and evaluate the volume of MSU by software (VOLUME, Siemens, Germany). There was no disagreement between the two readers regarding the presence of crystal deposits because of the objective criteria. They evaluated the possible presence of image artifacts which were defined as infinitesimal scattered pixilation and could be found to occur at certain sites including on the skin, within and around nail beds, along flexor tendons of the feet and hands, and along peroneal tendons. As well, motion could also result in artifacts mimicking MSU deposits. 2.5. Histopathology Twenty-four patients underwent the arthroscopic surgery and surgical resection. Tissue samples from tophi were fixed in 10% neutral buffered formalin and processed routinely for paraffin embedding followed by sectioning and staining with hematoxylin and eosin. 3. Results 3.1. Clinical characteristics
Fig. 1. Syngo dual-energy gout software (Siemens Healthcare). Screen shot of gout algorithm shows differences in attenuation between trabecular bone, uric acid, and cortical bone: The y-axis represents the attenuation values of the lower-kilovoltage tube (80 kV), and the x-axis represents the attenuation values of the higher-kilovoltage tube (140 kV). Pixels above the line represent calcium, and the pixels below the line represent uric acid (lower atomic numbers of its component elements).
One hundred sixty-one patients (154 male and 7 female) were enrolled in the gout group, who met the criteria of diagnosis of gout as defined by the American College of Rheumatology in 1977. Their ages ranged from 17 to 90 years (median age, 51±15 years). The serum uric acid (UA) level ranged from 189.4 to 1138.7 μmol/L; 130 patients had elevated serum uric acid level. The courses were from several days to more than 20 years. Eighty-nine patients had the history of gouty arthritis, 77 patients suffered from moderate to serious knee joints pain or swelling, 45 patients had an episode of acute arthritis that mainly involved the first metatarsophalangeal joints (MPJs) and the distal areas of the toes, 36 patients complained of attack of arthritis affecting the ankle areas, 2 patients complained of wrist joints attack, and 1 had involvement of the elbow joints. In the gout group, several comorbidities were observed, including hypertension (n=62), hyperlipidemia (n= 17), recurrent stones of the urinary system, gouty nephropathy or renal insufficiency (n=14), diabetes (n=23), and cardiovascular and cerebrovascular diseases (n=11). Thirty-two men and 9 women with a median age of 55±19 years (ages, 16–87 years) were recruited into the without-gout group. The
Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
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serum uric acid ranged from 114.9 to 551.9 μmol/L; serum uric acid level increased only in five cases. In the without-gout group, rheumatoid arthritis (n=3), osteoarthritis (n=13), joint and tendon injuries (n=6), infectious arthritis (n=1), asymptomatic hyperuricemia (n=3), synovial osteochondromatosis (n=1), and unclear reason (n=14). Their basic information and clinical characteristics are summarized in Table 1. 3.2. Imaging features In the gout group, 121 patients and 379 positions with urate deposition were found. The number of areas of urate deposition ranged from 0 to 9. The most common area of deposition in patients with gout was the ligaments (146/379), tendons (72/379), meniscus and synovial membrane (33/379), the first MPJ area (27/379), the ankle area (27/379), Achilles tendons(18/379), and the subcutaneous tissue (8/379) (Fig. 2). Additionally, punctate deposits (357/379) and multiple deposits (306/379) were more likely to be observed. The sensitivity and specificity were 75.2% and 92.7%, respectively. In the without-gout group, only three areas of punctuate urate deposition in the flexor tendon were found. In the gout group, we did not find urate deposition in 27 patients with clinical diagnosis of gouty arthritis in DECT and conventional CT imaging; and in 8 patients, we found the urate depositions in the conventional CT imaging (Fig.3A), but no deposits were found in the color-coded images (Fig.3B). Interestingly, when we increased the ratio to 1.32 and decreased the range to 3, we could find urate deposition in the flexor tendon, Achilles tendons, MPJ, meniscus, synovial membrane, and the ankle area (Fig.3C). When we increased the ratio to 1.32 and decreased the range to 3, the sensitivity and specificity were 91.9% and 85.4%. Five patients underwent DECT scans before and after treatment. The DECT images illustrated the palpable reduction in the tissue urate deposits compared to baseline images (Fig.4A and B). Twenty-four patients underwent arthroscopic surgery and surgical resection; the operative findings were identical with those of DECT (Table 2). The pathological findings confirmed the diagnosis of gout (Fig. 5). 4. Discussion Gouty arthritis is an increasingly common disease worldwide [17–19]. Patients who develop gout are more likely to be N 50 years of age [20]; however, because of shifts in diet and lifestyle, the age of onset was getting younger and younger. In this study, there are some very young patients. The prevalence of gout is much higher in men than in women and rises with age [21]. In our patients with gouty arthritis, the male:female ratio is 22:1. Serum uric acid level is the most important risk factor for gout. The primary biochemical abnormality in gout is an increase in serum urate Table 1 Demographic characteristics of the patients in this study
Clinical data Age, years (range) Sex (F/M) Disease duration (months)
Gout (n=161)
Control group (n=40)
51±15 (17–90) 1:22 55±71 0–480
55±19 (16–87) 1:3.6 32±57 0–360
Laboratory examinations Normal Renal function Gouty nephropathy, renal insufficiency (n=14) Blood uric acid 475.1±132.1 (189.4–1138.7) 349.5±102.6 (114.9–551.9) (μmol/L) (range)
Fig. 2. In the sagittal image of DECT, MSU crystals in the subcutaneous tissue are shown in green (red arrow); cortical bone color coded in blue and medullary bone in pink.
(SU) concentration. When supersaturation concentrations are reached, 6.8 mg/dl (0.41 mmol/L) at 37 °C, MSU crystals may form and can deposit in joints and periarticular tissue. Once deposited, MSU crystals cause damage through tophus formation and chronic gouty synovitis [22].Thus, SU is regarded as a critical measurement of gout. The presence of tophi in patients with gout is associated with higher SU concentrations. SU was significantly higher in patients with clinically evident tophi compared with those without tophi [23]. In our study, 126 patients had elevation of SU level in the gout group, but in the withoutgout group, SU level rose only in 5 patients, which was in agreement with the literature. However, the information about UA was not sufficient to distinguish gout and nongout patients. About 40% of patients with acute gout have a normal serum uric acid level during the attack, possibly as a result of proinflammatory cytokines [24]. Some patients with high SU level never develop symptoms associated with uric acid excess, such as gouty arthritis, tophi. In our study, the serum uric acid level were normal in 21.7% (35/161) of gouty arthritis patients. The presence of MSU crystals has been considered as the gold standard for the diagnosis of gout. However, some samples of joint fluid frequently are not obtained; or joint aspiration can be technically difficult, and there is a risk of complications [1]; and in the acute setting of acute gout, that aspiration can be negative 25% of the time [25]. So, a noninvasive, sensitive, and specific method of diagnosing gout is highly desirable. Imaging may play an important role in the diagnosis and assessment in patients of chronic gout. But other types of inflammatory arthritis, especially pseudogout, are similar to gout. Because of their overlapping symptoms and laboratory markers, it may be difficult to distinguish them clinically. DECT findings may be valuable in excluding urate crystal, and they have been shown to help distinguish gout from inflammatory mimics such as psoriasis, rheumatoid arthritis, pseudogout, and pigmented villonodular synovitis [13]. Pseudogout (calcium pyrophosphate deposition disease) is mainly made of elements such as calcium and phosphorus, with high atomic number, so it has a higher change in attenuation than MSU crystals. By DE gout software, it is colored blue, and gouty arthritis is colored green. DECT is highly accurate for identification of uric acid renal calculi and for differentiation from calcium-containing calculi both in vivo and in vitro [6,7]. Recently, DECT imaging has been used in the clinical diagnosis and treatment of gout as an emerging new method and has a high value for the assessment of gout [26–28], Some literature had described the ability of DECT in detecting MSU. Choi et al. [13] noted that DECT can help identify subclinical tophi. Nicolaou et al. [10] found that DECT was a useful diagnostic tool in the management of acute onset of gout. Glazebrook et al. [15] verified the diagnostic accuracy of DECT in a retrospective study of 31 patients with suspected gout who had both joint aspiration and DECT of the affected joint.
Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
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Fig. 4. A 64-year-old man had the history of gouty arthritis for 15 years, L. He underwent urate-lowering therapy. (A) In the 3D-VRT images of DECT color-coded imaging, multiple MSU crystals in the cruciate ligaments and the lateral collateral ligaments. (B) After uricolytic therapy. The volume of MSU crystals reduced significantly.
Fig. 3. A 64-year-old man had the diagnosis of gouty arthritis. The UA level was 440. 5 μmol/L. (A) In the transverse section images of conventional CT. The high density MSU crystals were seen in the Achilles tendon (blue arrow). (B) In DECT color-coded images, we no MSU crystals were seen. (C) When the ratio was increased to 1.32 and range was decreased to 3, the green MSU crystals could be seen.
In this study, we applied DECT to confirm the presence of MSU deposits within joints and soft tissues, as well as analyzed the distributions and features of urate crystals in patients with gouty arthritis. The results demonstrated that the patients with MSU crystals were more than the without-gout group, and the distributions of urate deposition in
patients with gout were more extensive. Urate deposits were found in 121/161 patients with gouty arthritis and only in 3/41 patients without gouty arthritis; the sensitivity and specificity were75.2% and 92.7%, respectively. In the 24 patients with surgery, the distribution of MSU crystals in DECT findings had high consistency with arthroscopy, and the pathology result identified the diagnosis of gout. When we modified the ratio and range, urate deposits were found in 148/161 patients with acute gouty arthritis and in 6/41 patients without gouty arthritis; the sensitivity and specificity were 91.9% and 85.4%, which indicated a similar sensitivity (93%)and specificity(78%) for DECT imaging for detecting urate deposits compared to the study by Choi et al. [29]. The result indicated that the settings of ratio and range were very important. Increasing the ratio and decreasing the range could improve the sensitivity of detecting MSU at the expense of decreasing specificity. Employing this technique we could make questionable areas of MSU deposition more discernable and increase the confidence of diagnosis. McQueen et al. [30] had reported that changes in the predefined machine settings such as the ratio parameter may lead to false-negative as well as false-positive diagnoses. Thus, when we suspect that the patient had gouty arthritis but there are no green MSU crystals in DECT scan, we should modify the ratio and range.
Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
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Table 2 Arthroscopy and surgery characteristics and DECT imaging findings of 24 patients Sex
Age SUA Scanning Arthroscopy and surgery (MSU position) (years) (μmol/L) position
Patient 1
Male 55
472.6
Knee
Patient 2
Male 26
715.1
Knee
Patient 3
Male 49
370.2
Knee
Patient 4
Male 36
468.5
Knee
Patient 5
Male 50
536.8
Knee
Patient 6
Male 45
413.2
Knee
Patient 7
Male 49
488
Knee
Patient 8
Male 32
581.3
Knee
Patient 9
Male 47
341.5
Knee
Patient 10 Patient 11 Patient 12
Male 47 Male 37 Male 48
495.3 498.1 513.0
Knee Foot Knee
Patient 13 Patient 14
Male 54 Male 55
487.6 435.2
Foot Knee
Patient 15
Male 45
624.6
Knee
Patient 16 Patient 17
Male 63 Male 58
510.8 417.6
Foot Knee
Patient 18 Patient 19 Patient 20 Patient 21
Male Male Male Male
77 66 64 46
425.7 351.1 614.0 400.8
Foot Foot Elbow Knee
Patient 22
Male 46
403.3
Knee
Patient 23 Patient 24
Male 66 Male 55
303.2 507.9
Knee Knee
Cruciate ligaments, meniscuses, synovial membrane, and cartilage Meniscuses, synovial membrane, and cartilage Anterior cruciate ligament, articular cavity and suprapatellar bursa, body of the lateral meniscus Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia Cruciate ligaments, lateral meniscus, synovial membrane and cartilage, lateral condyle of femur and tibia Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Meniscus, synovial membrane and cartilage
DECT (MSU position)
Posterior cruciate ligament, meniscuses, synovial membrane, and cartilage Meniscuses, synovial membrane and cartilage, cruciate ligaments No
Posterior cruciate ligament, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia Cruciate ligaments, lateral meniscus, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, quadriceps' tendon Meniscus, synovial membrane and cartilage, collateral ligaments Cruciate ligaments, meniscuses, Cruciate ligaments, meniscuses, The first MPJ area The first MPJ area, ankle area Cruciate ligaments, meniscuses, synovial membrane and Cruciate ligaments, meniscuses, synovial membrane and cartilage, quadriceps' tendon cartilage, quadriceps' tendon subcutaneous tissue of plantar subcutaneous tissue of plantar Cruciate ligaments, meniscuses, synovial membrane and Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, cartilage, collateral ligaments Cruciate ligaments, meniscuses, synovial membrane and Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, cartilage, collateral ligaments The first MPJ area The first MPJ area, flexor hallucis longus Cruciate ligaments, meniscuses, synovial membrane and Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, cartilage, lateral condyle of femur and tibia, Subcutaneous tissue Subcutaneous tissue The first MPJ area The first and third MPJ area Subcutaneous tissue Subcutaneous tissue Cruciate ligaments, meniscuses, synovial membrane and cartilage, Cruciate ligaments, meniscuses, synovial membrane and cartilage, Cruciate ligaments, meniscuses, synovial membrane and cartilage, Cruciate ligaments, meniscuses, synovial membrane and cartilage, Quadriceps' tendon Quadriceps' tendon, lateral condyle of femur Synovial membrane and cartilage, meniscuses Synovial membrane and cartilage, meniscuses
For the negative results in 40 patients with gouty arthritis, we speculated the following reasons: (a) in the acute phase, macrophages would be activated to engulf small urate deposits, and the local inflammatory environment as well as tissue pH change would further promote the resolution of the urate deposits [31]. (b) In the early stages of gout, the MSU deposits were microscopic deposits within the joint rather than macroscopic tophi. These crystals would be visible on polarized light microscopy, but the deposits may be too small to be detected using the DECT [32]. (c) The machine settings can influence the ability of detecting tophi [30]. (d) Some urate deposits were too small to be displayed in the color-coded results. (e) The parameters settings of the gout software also can influence the ability of detecting tophi. In this study, when we increased the ratio and decreased the range, the patients with urate deposits increased, and the locations of urate deposits were more extensive. But employing this technique we could get falsepositive results because of decreasing specificity. DECT was also useful for monitoring of the disease and measuring the volume of MSU. Choi et al. [29] indicated with prospective data a high reproducibility for DECT urate volume measures. Bacani et al. [33] quantified tissue urate deposits with the help of DECT before and after uricolytic therapy. Choi et al. [13] used an automated
Fig. 5. Low-magnification hematoxylin–eosin photomicrograph of tophi in knee displaying deposits of amorphous material with a surrounding granulomatous inflammation.
Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
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volumetric assessment of DECT to measure the volume of MSU deposits in all peripheral joint areas. Results showed that the scan had 100% accuracy for diagnosing gout. In this case, five patients underwent DECT scans before and after treatment with effective urate-lowering therapy; we found significant change of the volume of urate depositions intuitively. In summary, DECT is a very important method in noninvasive assessment of gout. It is the only method of imaging that enables direct visualization of urate deposition. Data suggest high diagnostic accuracy of gout in patients with established disease and almost complete reliability in rapid, automated volume assessment of urate burden. But there are some limitations in this study: (a) The field of view (FOV) of small tube is 27 cm, so the patients must be posed in the center of the FOV, and some patients with elevated body mass index may be ruled out. (b) Changes in the predefined machine settings such as the ratio parameter may lead to false-negative as well as false-positive diagnoses, so we need more clinical and pathological research so that we can get the best parameters for detecting MUS. (c) The sensitivity and specificity of DECT in detecting urate crystal deposits compared with the gold standard of histology have not yet been determined; we need further pathological research.
Authors’ Contributions H.H., M.L., and L.X. were involved with formation of the study concept and drafting of the manuscript. H.H. was the main contributor in the writing of the manuscript; M.L. and L.X. evaluated the DECT image. The authors declared that they had no competing interests. This study was supported by the Key Foundation of Hubei Health Scientific Funds (JX6B72).
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Clinical utility of dual-energy CT for gout diagnosis Hui-Juan Hu, Mei-Yan Liao ⁎, Li-Ying Xu Department of computed tomography, Zhongnan Hospital of Wuhan University, 169 East Lake Road, Wuhan 430071, PR China
a r t i c l e
i n f o
Article history: Received 16 June 2014 Received in revised form 4 December 2014 Accepted 24 December 2014 Available online xxxx Keywords: Gout Dual-energy CT Urate crystal Tophi
a b s t r a c t Objective: The present study was to evaluate the clinical value of dual-energy computed tomography (DECT) for detecting monosodium urate crystals in patients with gouty arthritis. Methods: Two hundred and two patients, who experienced arthrocele and (or) joint pain, were enrolled into our study. DECT scans of upper or lower extremity were performed. One hundred and sixty one patients who conformed to the American College of Rheumatology classification standard were defined as the gout group. The rest (41) of the patients were regarded as the without-gout group. DE (80 kV/140 kV) datasets were reconstructed via DE gout software. Images were reviewed independently by two senior radiologists. Results: In the gout group, DECT scans revealed a total of 379 areas of urate deposition in 121 patients. In the without-gout group, 3 areas of green urate deposition were detected. The sensitivity and specificity were 75.2% and 92.7%, respectively; when we increased the ratio to 1.32 and decreased the range to 3, the number of patients with green urate deposition increased, and the areas of urate deposition were more extensive. The sensitivity and specificity were 91.9% and 85.4%. DECT images could illustrate the palpable reduction in the tissue urate deposits compared to baseline images before and after treatment. Conclusions: DECT has comparable sensitivity and specificity for the detection of gouty arthritis in a clinical setting, and DECT can monitor the clinical treatment. However, DECT results should be interpreted carefully because there could be some false-negative or false-positive findings. © 2014 Published by Elsevier Inc.
1. Introduction Gout is characterized as a metabolic disorder in which there is either an increase in the production of uric acid or a decrease in the excretion of uric acid, resulting in hyperuricemia [1]. Long-lasting hyperuricemia causes deposition of monosodium urate (MSU) crystals in the joints and soft tissues, triggering gouty arthritis and, if not properly treated, the formation of gouty tophi [2]. An increased incidence and prevalence of gout has been reported, it is generally attributed to trends in lifestyles leading to increases in gout risk factors, such as obesity, metabolic syndrome, hypertension and alcohol consumption [3], at least 1% to 2% of all adults in the industrialized nations are now affected by gout [4]. The repeated recurrence of the gouty arthritis can cause deformity and disability, and it is strongly associated with metabolic syndrome, myocardial infarction, insulin resistance, stroke, and premature death, affecting patient’s quality of life and work severely [5–9]. For these reasons, early diagnosis and treatment are very important. Establishing a diagnosis of gout on the basis of clinical and laboratory criteria is generally straightforward. There are several other diseases that can mimic or coexist with gout, including septic arthritis, reactive arthritis, rheumatoid arthritis, osteoarthritis, erosive osteoarthritis, psoriasis, calcium pyrophosphate dihydrate crystal deposition, amyloidosis, pigmented ⁎ Corresponding author. Department of CT, Zhongnan Hospital of Wuhan University, 169 East Lake Road, Hubei, Wuhan, P.R. China. Tel.:+86 18971096590. E-mail addresses: [email protected] (H.-J. Hu), [email protected] (M.-Y. Liao), [email protected] (L.-Y. Xu).
villonodular synovitis, amyloid arthropathy, sarcoidosis, and so on [10,11], which may obscure or delay clinical diagnosis and affect patient treatment. The current common imaging techniques used to confirm and monitor gout include radiography, ultrasound, computed tomography (CT), and magnetic resonance imaging. However, these techniques are not specific enough to facilitate the diagnosis of gout [12]. The presence of MSU crystals would confirm the diagnosis of gout, so the optimal imaging technique should be highly specific for MSU deposition. The advent of dual-energy CT (DECT) has the potential to reach the aim. Dual-source CT scanners are equipped with two X-ray tubes allowing simultaneous acquisition at two different energy levels; thus, it is superior to the present single-energy (single-source) CT because of its ability to extract information and characterize the chemical composition of material according to the differential X-ray photon energydependent attenuation of the compounds being examined at the two different energy levels [10]. Utilizing this ability, DECT has been successfully shown in the literature to confirm the presence of MSU crystals in and around joints in gout arthropathy [13–15]. In this article, we demonstrate the ability of DECT to detect MSU deposition in gouty arthritis patients. 2. Materials and methods 2.1. Patients We retrospectively evaluated the imaging and clinical data of 202 patients who experienced joint swelling and (or) pain between October
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2010 and December 2013. Written informed consents were obtained from these patients. All information on patient demographic data, clinical and laboratorial presentation, underlying diseases, imaging manifestations, and pathological findings were recorded. 2.2. DECT examination DECT scans of upper or lower extremity were performed in 398 joints in different anatomical regions, such as the hands and wrists, elbows, knees, ankles, and feet. A 64-row dual-source CT scanner (Somatom Definition; Siemens, Germany) equipped with two X-ray tubes and detectors was used. In upper extremity scans, patients were positioned head first in a prone position. Forearms and wrists were positioned forward of the patient’s head with hands in a neutral position. Palms were placed with the dorsum facing up in a relaxed dorsiflexion position. In lower extremity scans, patients were positioned feet first in a supine position, with the knees bent approximately in a 90° position, with the feet in a firm plantarflexion position. The scan parameters were as follows: tube A: 140 kV, tube B: 80 kV, collimation 64×0.6 mm, pitch 0.7; dual-energy tube current parameters were different according to the scanned anatomical region: tube A reference (ref.) milliampere second (mAs) =40, tube B ref. mAs =170, for hands and wrists, elbows; and tube A ref. mAs=55, tube B ref. mAs=234, for ankles, feet, and knees. All scans were obtained without intravenous contrast agent. Transverse sections were reconstructed from the DE datasets, with a slice thickness of 0.75 mm and with a composition of 0.3 in the soft tissue kernel (D30). 2.3. Postprocessing and interpretation The transverse datasets of both tubes were loaded onto Syngo MultiModality Work-place (Siemens, Forchheim, Germany) and reconstructed with available software program (DE Gout; Siemens, Germany). Then, an image-based two-material decomposition algorithm of the datasets was subsequently performed to separate calcium from MSU, using soft tissue as the baseline (Fig. 1) The material-specific differences in attenuation of the two datasets (80 and 140 kVp) enabled an easy classification of the elementary chemical composition of the scanned tissue, allowing accurate characterization of uric acid (color coded in green) separately from the calcium and bone marrow (cortical bone color coded in blue and medullary bone in pink) [12].
The two-material decomposition algorithm is based on the physical principle that attenuation of photons depends on atomic number and energy of the photons. Material with a high atomic number (e.g., calcium) has a higher change in attenuation than does material with low-atomic-number components (e.g., uric acid). This difference in attenuation directly translates into a difference in CT values. The y-axis represents the attenuation values of the lower-kilovoltage tube (80 kV), and the x-axis represents the attenuation values of the higher-kilovoltage tube (140 kV). Pixels with a higher slope (high atomic number) are plotted above the line and represent calcium; the pixels below the line represent uric acid (lower atomic numbers of its component elements) [12]. 2.4. Image evaluation The base material “soft tissue” was chosen to be at 80 kV (50 HU) and at 140 kV (50HU), ratio 1.25, range 5; the range of values for the calculation was set between 125 and 3,000.The parameter ratio meant the slope of the separation line; we can find more MSU by increasing the ratio. Range meant smooth filter of pixel; it can increase density resolution while missing some detail. Thus, if the patient with clinical suspicion of gout had no MSU crystals, we would increase the ratio to 1.32 and decrease the range to 3 [16]. DECT images were evaluated by two senior radiologists. The readers were blinded to the patients’ clinical data. They read the images independently in the workplace. The readers were asked to classify the examination findings as positive or negative for the presence of MSU crystals, record the places of urate deposition, and evaluate the volume of MSU by software (VOLUME, Siemens, Germany). There was no disagreement between the two readers regarding the presence of crystal deposits because of the objective criteria. They evaluated the possible presence of image artifacts which were defined as infinitesimal scattered pixilation and could be found to occur at certain sites including on the skin, within and around nail beds, along flexor tendons of the feet and hands, and along peroneal tendons. As well, motion could also result in artifacts mimicking MSU deposits. 2.5. Histopathology Twenty-four patients underwent the arthroscopic surgery and surgical resection. Tissue samples from tophi were fixed in 10% neutral buffered formalin and processed routinely for paraffin embedding followed by sectioning and staining with hematoxylin and eosin. 3. Results 3.1. Clinical characteristics
Fig. 1. Syngo dual-energy gout software (Siemens Healthcare). Screen shot of gout algorithm shows differences in attenuation between trabecular bone, uric acid, and cortical bone: The y-axis represents the attenuation values of the lower-kilovoltage tube (80 kV), and the x-axis represents the attenuation values of the higher-kilovoltage tube (140 kV). Pixels above the line represent calcium, and the pixels below the line represent uric acid (lower atomic numbers of its component elements).
One hundred sixty-one patients (154 male and 7 female) were enrolled in the gout group, who met the criteria of diagnosis of gout as defined by the American College of Rheumatology in 1977. Their ages ranged from 17 to 90 years (median age, 51±15 years). The serum uric acid (UA) level ranged from 189.4 to 1138.7 μmol/L; 130 patients had elevated serum uric acid level. The courses were from several days to more than 20 years. Eighty-nine patients had the history of gouty arthritis, 77 patients suffered from moderate to serious knee joints pain or swelling, 45 patients had an episode of acute arthritis that mainly involved the first metatarsophalangeal joints (MPJs) and the distal areas of the toes, 36 patients complained of attack of arthritis affecting the ankle areas, 2 patients complained of wrist joints attack, and 1 had involvement of the elbow joints. In the gout group, several comorbidities were observed, including hypertension (n=62), hyperlipidemia (n= 17), recurrent stones of the urinary system, gouty nephropathy or renal insufficiency (n=14), diabetes (n=23), and cardiovascular and cerebrovascular diseases (n=11). Thirty-two men and 9 women with a median age of 55±19 years (ages, 16–87 years) were recruited into the without-gout group. The
Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
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serum uric acid ranged from 114.9 to 551.9 μmol/L; serum uric acid level increased only in five cases. In the without-gout group, rheumatoid arthritis (n=3), osteoarthritis (n=13), joint and tendon injuries (n=6), infectious arthritis (n=1), asymptomatic hyperuricemia (n=3), synovial osteochondromatosis (n=1), and unclear reason (n=14). Their basic information and clinical characteristics are summarized in Table 1. 3.2. Imaging features In the gout group, 121 patients and 379 positions with urate deposition were found. The number of areas of urate deposition ranged from 0 to 9. The most common area of deposition in patients with gout was the ligaments (146/379), tendons (72/379), meniscus and synovial membrane (33/379), the first MPJ area (27/379), the ankle area (27/379), Achilles tendons(18/379), and the subcutaneous tissue (8/379) (Fig. 2). Additionally, punctate deposits (357/379) and multiple deposits (306/379) were more likely to be observed. The sensitivity and specificity were 75.2% and 92.7%, respectively. In the without-gout group, only three areas of punctuate urate deposition in the flexor tendon were found. In the gout group, we did not find urate deposition in 27 patients with clinical diagnosis of gouty arthritis in DECT and conventional CT imaging; and in 8 patients, we found the urate depositions in the conventional CT imaging (Fig.3A), but no deposits were found in the color-coded images (Fig.3B). Interestingly, when we increased the ratio to 1.32 and decreased the range to 3, we could find urate deposition in the flexor tendon, Achilles tendons, MPJ, meniscus, synovial membrane, and the ankle area (Fig.3C). When we increased the ratio to 1.32 and decreased the range to 3, the sensitivity and specificity were 91.9% and 85.4%. Five patients underwent DECT scans before and after treatment. The DECT images illustrated the palpable reduction in the tissue urate deposits compared to baseline images (Fig.4A and B). Twenty-four patients underwent arthroscopic surgery and surgical resection; the operative findings were identical with those of DECT (Table 2). The pathological findings confirmed the diagnosis of gout (Fig. 5). 4. Discussion Gouty arthritis is an increasingly common disease worldwide [17–19]. Patients who develop gout are more likely to be N 50 years of age [20]; however, because of shifts in diet and lifestyle, the age of onset was getting younger and younger. In this study, there are some very young patients. The prevalence of gout is much higher in men than in women and rises with age [21]. In our patients with gouty arthritis, the male:female ratio is 22:1. Serum uric acid level is the most important risk factor for gout. The primary biochemical abnormality in gout is an increase in serum urate Table 1 Demographic characteristics of the patients in this study
Clinical data Age, years (range) Sex (F/M) Disease duration (months)
Gout (n=161)
Control group (n=40)
51±15 (17–90) 1:22 55±71 0–480
55±19 (16–87) 1:3.6 32±57 0–360
Laboratory examinations Normal Renal function Gouty nephropathy, renal insufficiency (n=14) Blood uric acid 475.1±132.1 (189.4–1138.7) 349.5±102.6 (114.9–551.9) (μmol/L) (range)
Fig. 2. In the sagittal image of DECT, MSU crystals in the subcutaneous tissue are shown in green (red arrow); cortical bone color coded in blue and medullary bone in pink.
(SU) concentration. When supersaturation concentrations are reached, 6.8 mg/dl (0.41 mmol/L) at 37 °C, MSU crystals may form and can deposit in joints and periarticular tissue. Once deposited, MSU crystals cause damage through tophus formation and chronic gouty synovitis [22].Thus, SU is regarded as a critical measurement of gout. The presence of tophi in patients with gout is associated with higher SU concentrations. SU was significantly higher in patients with clinically evident tophi compared with those without tophi [23]. In our study, 126 patients had elevation of SU level in the gout group, but in the withoutgout group, SU level rose only in 5 patients, which was in agreement with the literature. However, the information about UA was not sufficient to distinguish gout and nongout patients. About 40% of patients with acute gout have a normal serum uric acid level during the attack, possibly as a result of proinflammatory cytokines [24]. Some patients with high SU level never develop symptoms associated with uric acid excess, such as gouty arthritis, tophi. In our study, the serum uric acid level were normal in 21.7% (35/161) of gouty arthritis patients. The presence of MSU crystals has been considered as the gold standard for the diagnosis of gout. However, some samples of joint fluid frequently are not obtained; or joint aspiration can be technically difficult, and there is a risk of complications [1]; and in the acute setting of acute gout, that aspiration can be negative 25% of the time [25]. So, a noninvasive, sensitive, and specific method of diagnosing gout is highly desirable. Imaging may play an important role in the diagnosis and assessment in patients of chronic gout. But other types of inflammatory arthritis, especially pseudogout, are similar to gout. Because of their overlapping symptoms and laboratory markers, it may be difficult to distinguish them clinically. DECT findings may be valuable in excluding urate crystal, and they have been shown to help distinguish gout from inflammatory mimics such as psoriasis, rheumatoid arthritis, pseudogout, and pigmented villonodular synovitis [13]. Pseudogout (calcium pyrophosphate deposition disease) is mainly made of elements such as calcium and phosphorus, with high atomic number, so it has a higher change in attenuation than MSU crystals. By DE gout software, it is colored blue, and gouty arthritis is colored green. DECT is highly accurate for identification of uric acid renal calculi and for differentiation from calcium-containing calculi both in vivo and in vitro [6,7]. Recently, DECT imaging has been used in the clinical diagnosis and treatment of gout as an emerging new method and has a high value for the assessment of gout [26–28], Some literature had described the ability of DECT in detecting MSU. Choi et al. [13] noted that DECT can help identify subclinical tophi. Nicolaou et al. [10] found that DECT was a useful diagnostic tool in the management of acute onset of gout. Glazebrook et al. [15] verified the diagnostic accuracy of DECT in a retrospective study of 31 patients with suspected gout who had both joint aspiration and DECT of the affected joint.
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Fig. 4. A 64-year-old man had the history of gouty arthritis for 15 years, L. He underwent urate-lowering therapy. (A) In the 3D-VRT images of DECT color-coded imaging, multiple MSU crystals in the cruciate ligaments and the lateral collateral ligaments. (B) After uricolytic therapy. The volume of MSU crystals reduced significantly.
Fig. 3. A 64-year-old man had the diagnosis of gouty arthritis. The UA level was 440. 5 μmol/L. (A) In the transverse section images of conventional CT. The high density MSU crystals were seen in the Achilles tendon (blue arrow). (B) In DECT color-coded images, we no MSU crystals were seen. (C) When the ratio was increased to 1.32 and range was decreased to 3, the green MSU crystals could be seen.
In this study, we applied DECT to confirm the presence of MSU deposits within joints and soft tissues, as well as analyzed the distributions and features of urate crystals in patients with gouty arthritis. The results demonstrated that the patients with MSU crystals were more than the without-gout group, and the distributions of urate deposition in
patients with gout were more extensive. Urate deposits were found in 121/161 patients with gouty arthritis and only in 3/41 patients without gouty arthritis; the sensitivity and specificity were75.2% and 92.7%, respectively. In the 24 patients with surgery, the distribution of MSU crystals in DECT findings had high consistency with arthroscopy, and the pathology result identified the diagnosis of gout. When we modified the ratio and range, urate deposits were found in 148/161 patients with acute gouty arthritis and in 6/41 patients without gouty arthritis; the sensitivity and specificity were 91.9% and 85.4%, which indicated a similar sensitivity (93%)and specificity(78%) for DECT imaging for detecting urate deposits compared to the study by Choi et al. [29]. The result indicated that the settings of ratio and range were very important. Increasing the ratio and decreasing the range could improve the sensitivity of detecting MSU at the expense of decreasing specificity. Employing this technique we could make questionable areas of MSU deposition more discernable and increase the confidence of diagnosis. McQueen et al. [30] had reported that changes in the predefined machine settings such as the ratio parameter may lead to false-negative as well as false-positive diagnoses. Thus, when we suspect that the patient had gouty arthritis but there are no green MSU crystals in DECT scan, we should modify the ratio and range.
Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
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Table 2 Arthroscopy and surgery characteristics and DECT imaging findings of 24 patients Sex
Age SUA Scanning Arthroscopy and surgery (MSU position) (years) (μmol/L) position
Patient 1
Male 55
472.6
Knee
Patient 2
Male 26
715.1
Knee
Patient 3
Male 49
370.2
Knee
Patient 4
Male 36
468.5
Knee
Patient 5
Male 50
536.8
Knee
Patient 6
Male 45
413.2
Knee
Patient 7
Male 49
488
Knee
Patient 8
Male 32
581.3
Knee
Patient 9
Male 47
341.5
Knee
Patient 10 Patient 11 Patient 12
Male 47 Male 37 Male 48
495.3 498.1 513.0
Knee Foot Knee
Patient 13 Patient 14
Male 54 Male 55
487.6 435.2
Foot Knee
Patient 15
Male 45
624.6
Knee
Patient 16 Patient 17
Male 63 Male 58
510.8 417.6
Foot Knee
Patient 18 Patient 19 Patient 20 Patient 21
Male Male Male Male
77 66 64 46
425.7 351.1 614.0 400.8
Foot Foot Elbow Knee
Patient 22
Male 46
403.3
Knee
Patient 23 Patient 24
Male 66 Male 55
303.2 507.9
Knee Knee
Cruciate ligaments, meniscuses, synovial membrane, and cartilage Meniscuses, synovial membrane, and cartilage Anterior cruciate ligament, articular cavity and suprapatellar bursa, body of the lateral meniscus Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia Cruciate ligaments, lateral meniscus, synovial membrane and cartilage, lateral condyle of femur and tibia Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Meniscus, synovial membrane and cartilage
DECT (MSU position)
Posterior cruciate ligament, meniscuses, synovial membrane, and cartilage Meniscuses, synovial membrane and cartilage, cruciate ligaments No
Posterior cruciate ligament, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia Cruciate ligaments, lateral meniscus, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, quadriceps' tendon Cruciate ligaments, meniscuses, synovial membrane and cartilage, quadriceps' tendon Meniscus, synovial membrane and cartilage, collateral ligaments Cruciate ligaments, meniscuses, Cruciate ligaments, meniscuses, The first MPJ area The first MPJ area, ankle area Cruciate ligaments, meniscuses, synovial membrane and Cruciate ligaments, meniscuses, synovial membrane and cartilage, quadriceps' tendon cartilage, quadriceps' tendon subcutaneous tissue of plantar subcutaneous tissue of plantar Cruciate ligaments, meniscuses, synovial membrane and Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, cartilage, collateral ligaments Cruciate ligaments, meniscuses, synovial membrane and Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, cartilage, collateral ligaments The first MPJ area The first MPJ area, flexor hallucis longus Cruciate ligaments, meniscuses, synovial membrane and Cruciate ligaments, meniscuses, synovial membrane and cartilage, lateral condyle of femur and tibia, cartilage, lateral condyle of femur and tibia, Subcutaneous tissue Subcutaneous tissue The first MPJ area The first and third MPJ area Subcutaneous tissue Subcutaneous tissue Cruciate ligaments, meniscuses, synovial membrane and cartilage, Cruciate ligaments, meniscuses, synovial membrane and cartilage, Cruciate ligaments, meniscuses, synovial membrane and cartilage, Cruciate ligaments, meniscuses, synovial membrane and cartilage, Quadriceps' tendon Quadriceps' tendon, lateral condyle of femur Synovial membrane and cartilage, meniscuses Synovial membrane and cartilage, meniscuses
For the negative results in 40 patients with gouty arthritis, we speculated the following reasons: (a) in the acute phase, macrophages would be activated to engulf small urate deposits, and the local inflammatory environment as well as tissue pH change would further promote the resolution of the urate deposits [31]. (b) In the early stages of gout, the MSU deposits were microscopic deposits within the joint rather than macroscopic tophi. These crystals would be visible on polarized light microscopy, but the deposits may be too small to be detected using the DECT [32]. (c) The machine settings can influence the ability of detecting tophi [30]. (d) Some urate deposits were too small to be displayed in the color-coded results. (e) The parameters settings of the gout software also can influence the ability of detecting tophi. In this study, when we increased the ratio and decreased the range, the patients with urate deposits increased, and the locations of urate deposits were more extensive. But employing this technique we could get falsepositive results because of decreasing specificity. DECT was also useful for monitoring of the disease and measuring the volume of MSU. Choi et al. [29] indicated with prospective data a high reproducibility for DECT urate volume measures. Bacani et al. [33] quantified tissue urate deposits with the help of DECT before and after uricolytic therapy. Choi et al. [13] used an automated
Fig. 5. Low-magnification hematoxylin–eosin photomicrograph of tophi in knee displaying deposits of amorphous material with a surrounding granulomatous inflammation.
Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
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volumetric assessment of DECT to measure the volume of MSU deposits in all peripheral joint areas. Results showed that the scan had 100% accuracy for diagnosing gout. In this case, five patients underwent DECT scans before and after treatment with effective urate-lowering therapy; we found significant change of the volume of urate depositions intuitively. In summary, DECT is a very important method in noninvasive assessment of gout. It is the only method of imaging that enables direct visualization of urate deposition. Data suggest high diagnostic accuracy of gout in patients with established disease and almost complete reliability in rapid, automated volume assessment of urate burden. But there are some limitations in this study: (a) The field of view (FOV) of small tube is 27 cm, so the patients must be posed in the center of the FOV, and some patients with elevated body mass index may be ruled out. (b) Changes in the predefined machine settings such as the ratio parameter may lead to false-negative as well as false-positive diagnoses, so we need more clinical and pathological research so that we can get the best parameters for detecting MUS. (c) The sensitivity and specificity of DECT in detecting urate crystal deposits compared with the gold standard of histology have not yet been determined; we need further pathological research.
Authors’ Contributions H.H., M.L., and L.X. were involved with formation of the study concept and drafting of the manuscript. H.H. was the main contributor in the writing of the manuscript; M.L. and L.X. evaluated the DECT image. The authors declared that they had no competing interests. This study was supported by the Key Foundation of Hubei Health Scientific Funds (JX6B72).
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Please cite this article as: Hu H-J, et al, Clinical utility of dual-energy CT for gout diagnosis, Clin Imaging (2015), http://dx.doi.org/10.1016/ j.clinimag.2014.12.015
