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1125

Meeting

Liver Imaging-Current International Symposium Elizabeth

Trends in MRI, CT, and US: and Course, June 1990

Whalen1

“Liver Imaging: Current Trends in MRI, Cl, and US” (an international symposium and course sponsored by the Department of Radiology, Massachusetts General Hospital; The MGH Liver Biliary and Pancreas Center; and the Department of Continuing Education, Harvard Medical School) was held

June 25-27, 1 990, at the Copley Westin Hotel, Boston, MA. Some 60 invited lectures and 26 submitted scientific papers were presented by researchers from the United States and 1 0 foreign countries. The symposium was interdisciplinary as well as international: speakers included not only experts on liver imaging, but also gastroenterologists, biochemists, physicists, and representatives of the Food and Drug Administra-

tion (FDA) and the pharmaceutical

and imaging

industries. in the AJR preclude com-

Unfortunately, space limitations plete coverage of this intensive, 3-day symposium; however, we hope that this report will make our readers aware of the

latest advances and future directions in liver imaging. The symposium director, Joseph I. Ferrucci, stated its purposes: to focus on “current and future trends in imaging diagnosis of the liver,” “to identify the major trends that will affect radiologic diagnosis of abdominal diseases for the next decade,” and “to set the research agenda for imaging diagnosis of liver disease.” This report covers six major topics discussed during

the symposium:

imaging techniques

to detect hepatic lesions,

methods for characterization of hepatic tissue, imaging of hepatic metastases, the role of imaging in the planning and follow-up of hepatic surgery, new and developing techniques for liver imaging, and contrast agents for liver imaging. 1

Contributing

News

editor,

American

Journal

of Roentgenology,

Ste. 1 03, 2223

Avenida

Lesion

Detection

with

MR

Imaging,

CT,

and

Sonography

After overview lectures by Dr. Ferrucci and by codirector David D. Stark (both Massachusetts General Hospital, Boston), the first topic imaging techniques.

the use of different methods.

was the detection of liver lesions Lectures and scientific papers

imaging

methods

by using covered

and compared

those

CT

Patrick C. Freeny (Virginia Mason Clinic, Seattle, WA) discussed the techniques and results of four different Cl methods: bolus dynamic CT, delayed iodine scanning, Cl angiography, and CT arterial portography. Dr. Freeny suggested the following parameters as guidelines for these procedures: bolus dynamic CT, effective scanning parameters include

For nine

scans/sec, three-scan clusters, 2-sec scanning time, 3.5-sec interscan delay, 10-sec intergroup delay, and rapid uniphasic injection of 1 50-1 80 ml of 60% contrast material (ionic or nonionic);

this technique

works

well in either

abdominal

sur-

veys or liver surveys. For delayed iodine scanning, incremental Cl is performed 4-6 hr after administration of a dose of 60 g or more of iodine; with these parameters, liver enhancement is 20 H greater than baseline enhancement, and accurate liver surveys can be obtained. The following parameters can be used for both Cl angiography and CT arterial portography: A series

of five to eight clusters

de Ia Playa,

of three

2-sec

scans

is obtained

La Jolla, CA 92037.

Editor’s note.-Meeting News articles report the highlights of important national radiology meetings. The intent is to provide Joumal readers with succinct, substantive, and accurate reviews of topics of current interest, written in a readable fashion and published promptly after the meeting. The articles will not undergo the peer review usually required of AJR publications, nor will they offer a critique of the information provided. The sole purpose of the series is to apprise AJR readers of topics of current concern in an interesting and timely fashion. 155:1125-1132,

November

1990 0361-803x/90/i555-1

125 © American

Roentgen

Ray Society

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1126

MEETING

NEWS

AJR:155,

November

1990

with a 3.5-sec interscan delay for table incrementation and a 1 0-sec intergroup delay for patients to breathe. Cl angiog-

within the liver but inferior to Cl scans for lesions outside the liver. Dr. Stark and his coworkers concluded that enhanced

raphy is performed with selective injection of artery with a 1 5% contrast agent at 2 mI/sec three-scan cluster (total of 26 mI/cluster), and portography is performed by selective injection of

Cl should still be used for routine abdominal imaging. Heavily 12-weighted MR imaging is effective for differential diagnosis

the hepatic during each Cl arterial the superior

of primary or secondary, benign Preliminary data on the newer

mesenteric artery with 100-1 50 ml of a 60% contrast agent at a continuous rate of 2-3 mI/sec. Cl angiography of Cl arterial portography combined with delayed iodine scanning

Francisco). Ultra-low-field for the patient than other

is the most

the open design of the unit, which eliminates

useful

protocol

for hepatic

lesion

detection.

Dr. Freeny and colleagues have followed up 528 consecutive patients with various stages of cancer in whom Cl was used to detect liver metastases; 40 of those patients have had liver metastases proved at surgery. For detecting liver metastases, CT had a sensitivity of 88% and a specificity of 99%. In another study of 25 resected livers with 35 lesions, Dr. Freeny found that, for hepatic lesion detection, CT angiography plus MR imaging had a sensitivity of 87%; Cl angiography plus delayed iodine scanning had a sensitivity of 89%; and Cl angiography plus delayed iodine scanning and MR imaging had the highest sensitivity, 97%.

presented

or malignant ultra-low-field

by Ruedi F. Ihoeni

and because

of its silent

High-field W. Dennis

MR imaging Foley

(Medical

of hepatic lesions was discussed College

of Wisconsin,

by

Milwaukee).

Image contrast is an important factor in lesion conspicuity, and contrast depends on both the MR field strength and the pulse sequence. Anecdotal evidence suggests that the difference between the 11 of liver and the 11 of lesion may be greater at low to intermediate field strength than at high field strength and that the 12 value of normal liver may be lower at 1 .5 1 than at 3.5 1. In a high-field MR study of 46 hepatic lesions, more lesions were detected by T2-weighted (44) than by either 11 -weighted (30) or proton-density-weighted (35) imaging.

Also,

12-weighted

images

had

higher

contrast-to-

noise ratios. Presaturation reordered phase encoding and gradient moment nulling have become standard motion-compensation techniques for hepatic MR. Short inversion time recovery (STIR) pulse sequences neous fat while enhancing hepatic

null signal

from

subcuta-

lesion contrast. However, image quality is degraded relative to standard spin-echo sequences. Recent evidence indicates that Ti -weighted images with short echo times (TE5) may produce images with better contrast than that seen on standard 12-weighted images. Dr. Stark compared midfield MR images with CT scans of liver lesions. A 0.6-I imager was used, with a 1 .5-cm slice thickness,

a 25%

echo sequences, images produced

gap,

1 .8 x 3.6 mm

pixel

size,

two

spin-

and an inversion recovery sequence. The with this midfield technique were retrospec-

tively reviewed who compared

by three blinded, experienced radiologists, them with Cl scans obtained on a fourthgeneration scanner (80% of the CT scanning was performed with rapid scanning after administration of >40 g of iodinated

contrast material). Receiver-operating-characteristic (ROC) analysis of the results from 1 000 patients showed that these MR images were slightly better than Cl scans for lesions

operation.

of California,

San

allows more comfort methods because of

Low-field

claustrophobia, MR imaging

is

also more cost-effective; its purchase price, installation cost, and maintenance expenses are all lower than for mid- or highfield MR imaging. However, the current disadvantages of using low-field MR imaging include lower signal-to-noise ratio and spatial resolution than higher field techniques and the inadequate quality of short imaging sequences (particularly heavily 11-weighted sequences). Dr. Ihoeni and colleagues compared low-field and midfield MR images in patients with primary or metastatic liver lesions. Low-field imaging was performed on a 0.064-I (640-gauss) permanent magnet with a vertically oriented imaging liver lesions,

MR Imaging

(University

MR imaging MR imaging

liver lesions. MR units were

field and a solenoidal body coil. For low-field MR images were ranked equal

to midfield MR images in 65% of the patients, worse than midfield in 4%, and better than midfield in 31 %. Thus, in general, liver lesion margin and contrast was better on lowfield images.

However,

low-field

images

were generally

ranked

lower for imaging of the rest of the abdomen (80% were considered worse than midfield images; 1 6% were considered equal; and 4% were considered better than midfield images). More research will be conducted to try to improve low-field imaging of the entire abdomen and to create adequate 11weighted images with low-field MR imaging. At this point, low-field MR imaging is a cost-effective tool that provides excellent assessment of focal liver lesions. Steven

P. Braff

(Clifton

Springs

Hospitals

and Clinics,

Clif-

ton Springs, NY) discussed midfield MR imaging in a general clinical practice. Using a 0.4-I electromagnet, these radiologists

obtained

MR images

on 1 5 patients

for characterization

of hepatic lesions. MR examinations included some short-TE, short-IR studies; some long-TE, long-IR studies; and studies both with and without cardiac gating. Midfield MR imaging helped in screening for liver metastases, characterizing a known mass, clarifying an abnormal or suboptimal CT study, obtaining images in patients who have had adverse reactions

to contrast material, ruling out infiltrative disease, and ruling out liver lesions in patients with fatty infiltration of the liver. Dr. Braff said that MR imaging is now being their case load; he expects that percentage

MR technology

and their own expertise

used in 5-8% to increase

in MR imaging

of as

im-

prove.

Comparative A comparison

Studies of MR, CT, and sonographic

studies

of focal

liver lesions was presented by C. Dan Johnson (Mayo Clinic, Rochester, MN). All 30 patients in this prospective study had pathologically

proved

liver

lesions;

25 (83%)

had

malignant

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AJA:155,

November

MEETING

1990

lesions, and five (1 7%) had benign conditions. State-of-theart MR imaging, CT, and sonography were compared in terms of sensitivity of liver lesion detection, diagnostic confidence level, and characterization of liver lesion. No significant differences were found in the sensitivities of the three techniques (MR imaging, 80%; Cl, 77%; sonography, 73%). MR imaging was significantly better than sonography at characterizing lesions; no significant differences in lesion characterization were seen between MR imaging and CT or between CT and sonography. Analysis of the results indicated that sonography is best for studying cystic masses, CT is best for detecting lesions with calcification, and MR imaging is best for showing fat-containing lesions. Therefore, each patient’s history and previous imaging studies can be used to predict the most likely type of lesion and thus to help select the best imaging method.

Imaging

Methods

for Characterizing

Hepatic

Tissue

In the presentations on liver tissue characterization, specific topics included color-flow sonography, MR imaging in hydatid cysts of the liver, and comparison of different imaging techniques in characterization of liver tumors.

Color Doppler

Flow Sonography

F. Fobbe (Free University of Berlin, Berlin, West Germany) discussed the capability of color-coded duplex sonography to show the perfusion state of focal liver lesions. The specificity of real-time sonography is low for these determinations, and color sonography allows the display of flow from vessels too small to be seen on real-time images. Dr. Fobbe and colleagues performed a prospective study of color-coded duplex sonography in 96 patients; results were compared with Cl, angiographic, and histologic results. Comparison of flow signals in the 41 patients with primary liver lesions showed that the vascularity of tumors was not significantly higher than that of normal liver tissue. In the 55 patients with secondary liver lesions, they once again found no significant difference in vascularity between tumor and normal tissue (59% of the colon metastases showed more blood flow than normal tissue, but increased blood flow was seen in only 29% of the breast, stomach, and pancreas metastases). Color-coded duplex sonography is a simple, accurate, and rapid technique for demonstrating the vascularization of liver lesions, but it cannot distinguish between primary and secondary tumors nor can it reveal the primary site of liver metastases. In another study, Sachiko Tanaka and colleagues (The Center for Adult Diseases, Osaka, Japan) tried to establish which color flow patterns were most common to hepatocellular carcinomas by studying the color Doppler flow images of 31 patients with nodular hepatocellular carcinomas. Two characteristic pulsating-wave patterns were found: 22 (71%) displayed a basket pattern (a fine blood-flow network surrounding the tumor nodule), and 22 (71 %) displayed vessels within the tumor (blood flow that runs into and branches within the tumor). Of the 1 1 tumors that were smaller than 2 cm, eight showed the basket pattern, and seven showed

NEWS

1127

vessels within the tumor. Two constant-wave diagnostic patterns were seen: multiple hepatic metastases were often characterized by a detour pattern (a dilated portal vein meandering around the tumor nodules), and three of six hemangiomas had a spot pattern (color-stained dots in the tumor center). These results suggest the potential use of color flow patterns for distinguishing types of hepatic tumors; however, these patterns have not yet been proved to be definitive diagnostic signs.

MR Imaging

of Hydatid

Cysts

of the Liver

Roberto Passariello (University of L’Aquila, L’Aquila, Italy) investigated the preoperative and postoperative use of 0.5-I MR imaging to evaluate hydatid liver cysts. Ihe indications for MR imaging included doubtful sonographic findings, preoperative evaluation of extent of cyst and relationships of vessels, exact location of liver, characterization of lesion, identification of hepatic rupture, and postoperative evaluation of recurrent cyst. Preoperative MR evaluations were performed in 30 patients (cyst size, 3-1 0 cm), and postoperative MR images were obtained in three other patients. The cyst walls were best characterized on proton-density images; the wall was always hypointense (appearance of cyst content depended on lesion type), and a thickened wall indicated calcific areas. Three types ofliver hydatid cysts can be defined on the basis of MR findings: type 1 serous (n = 1 5 in this series)-markedly and homogeneously hypointense on Ti -weighted sequences; type 2, complex with daughter cysts (n = 4)-mildly hypointense on 11 -weighted sequences and hyperintense on matrix 12-weighted sequences; and type 3, calcified (n = 1 1 )-thickened hypointense wall with hyperintense contents, low signal intensity on 11 -weighted images, and high signal intensity on 12-weighted sequences. MR imaging easily identified intrahepatic cyst rupture, and postoperative MR evaluation helped determine the serous or blood content of the residual and the recurrence and extent of vascular lesions. Thus, for hydatid liver cysts, MR imaging may be able to replace Cl for clarification of cysts after indeterminate sonography, MR findings may help characterize the nature of a cystic lesion, and multiphasic MR imaging may assist in postoperative evaluation. ,

Comparative

Studies

A prospective study comparing different imaging methods for characterization of liver tumors was presented by Meinhard LUning (Charit#{233}Hospital, Humboldt University, Berlin, East Germany). The study group included 1 30 patients with histologically proved diagnoses of hemangioma (44), metastases (37), hepatocellular carcinoma (28), focal nodular hyperplasia (1 7), and adenoma (four). MR imaging was performed in all patients; dynamic CT in 1 22; sonography in 1 19; scintigraphy in 44; and CT arteriography in 1 5. In differentiating malignant from benign lesions, no significant difference was found between the imaging methods, although MR imaging appeared to have a moderate advantage (accuracies: MR imaging, 91 %; CT, 89%, Cl arteriography, 87%, sonog-

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1128

MEETING

raphy, 84%). MR imaging also had the highest accuracy in characterizing lesions (MR imaging, 80%; CT, 73%; Cl arteriography, 73%; sonography, 69%; scintigraphy, 53%). The best disease-specific accuracy was found in the MR imaging diagnosis of hemangiomas; the worst disease-specific accuracy was the sonographic diagnosis of focal nodular hyperplasias. Jeffrey C. Weinreb (New York University Medical Center, New York) presented the results of a retrospective study comparing MR imaging and TC-labeled-RBC single-photon emission CT (SPECT) in the definitive diagnosis of hepatic hemangiomas. In 38 patients, a total of 69 suspected cavernous hemangiomas had been detected by either CT or sonography. SPECT imaging was performed after the patient’s blood was labeled with 30 mCi (1 1 00 MBq) of technetium99m; after acquisition of a dynamic flow phase followed by an interval of 90-1 20 mm, delayed SPECT images were obtained, ultimately yielding 1 .2-cm-thick axial, coronal, and sagittal slices. Low-field (0.5-1) MR imaging and 12-weighted spin-echo sequences were used. The images were reviewed by two pairs of experienced radiologists; the readers were told of the location and size of the reference lesion but were not given the previous CT or sonographic studies. The likelihood of hemangioma was graded on a five-point confidence scale. Overall, MR imaging was slightly superior in sensitivity (MR imaging, 91 %; SPECT, 78%) and accuracy (MR imaging, 90%; SPECT, 80%). MR imaging was significantly more accurate in finding lesions less than 2 cm in diameter; there was no significant difference in accuracies for lesions larger than 2 cm. Also, MR imaging was more effective in identifying lesions less than 2.5 cm in diameter that were situated adjacent to major vessels or the heart. However, although MR imaging proved to be superior for lesions of certain size and location, its inability to differentiate hemangiomas from hypervascular metastases and its high cost make it an impractical first examination. Dr. Weinreb added that new tripleheaded gamma cameras improve SPECT resolution dramatically and make detection of hemangiomas as small as 5 mm possible. After observing that “when working toward a solution to a problem, it always helps to know the answer,” Dr. Weinreb noted that the radiologist will need to think of cayernous hemangiomas in order to see them on SPECT.

Imaging

Diagnoses

of Hepatic

Metastases

To determine whether serial CT scans can help to predict the progression of liver metastases from colonic carcinoma, R. A. Halvorsen, Jr., and colleagues (University of Minnesota, Minneapolis) evaluated 127 CT scans in 27 patients. Factors evaluated included the number and size of metastases in each hepatic segment, percentage of liver involvement, and subjective estimate of change in metastases’ volume; also, the metastases were characterized in terms of margination, contents (solid or cystic), calcification, mass effect, clefts, and rim enhancement. Changes in serial CT scans were correlated with each patient’s clinical status, as defined by level of carcinoembryonic antigen, weight changes, and/or date of death. Direct correlations were found between these clinical

NEWS

AJR:155,

indicators

November

1990

and a change in the size of the largest metastasis both sensitivity and specificity were 67% if a 1 -cm increase in diameter was used as the criterion for progression); a change in metastasis volume (p .02); and mass effect (p .024). The change in percentage of involvement showed a borderline correlation with progression (p = .085). None of the other factors evaluated showed a significant correlation with clinical progression; Dr. Halvorsen noted that the lack of correlation was especially interesting for contents of the metastasis (p = 71) and clefts on the surface of the liver (p = .95). Perhaps the most surprising finding was that calcification showed no correlation with disease progression (p = 1 .00). These researchers concluded that serial CT scans can be used to predict progression of hepatic metastases from colonic carcinoma: changes in the size of the largest metastasis and changes in its estimated volume on Cl appear to correlate directly with clinical indicators of progression. E. Rummeny (University of MUnster, M#{252}nster,West Germany) discussed a study in which CT and high-field MR imaging were compared in regard to detecting hepatic metastases. Dr. Rummeny and colleagues studied the ROCs of MR images and both enhanced and unenhanced CT scans. In total, 900 images were studied; 450 of subjects without disease and 450 of patients with primary cancer proved at laparotomy. MR images were obtained at 1 .5 1, by using Ti weighted spin-echo and gradient-echo, proton-densityweighted spin-echo, and 12-weighted presaturated spin-echo sequences. A third-generation CT scanner was used to obtain scans before, during, and 4-5 hr after a bolus injection of 200 ml of contrast material. ROC analysis indicated that, of all MR and CT techniques evaluated, the heavily 12-weighted MR sequence was the best technique for detecting liver metastases. Of the Cl methods, contrast-enhanced Cl scans were found to be more useful than either unenhanced or delayed scans; contrast-enhanced CT scans were approximately equivalent to gradient-echo 11 -weighted MR images for detection of metastases. Because CT scans show focal fatty infiltration of the liver and hepatic metastases as lesions of similar density, K. Neumann and colleagues (University Clinic Rudolf Virchow/ Charlottenburg, Free University of Berlin, Berlin, West Germany) studied the use of MR imaging for the differential diagnosis of these two disease processes. Third-generation CT units were used to obtain enhanced and unenhanced scans; Ti -weighted gradient-echo images and 12-weighted spin-echo images were generated on a 0.5-T MR imager. Of the 1 6 patients studied, 1 1 had liver metastases and five had focal fatty infiltration; CT scans of all 1 6 patients showed areas of decreased attenuation. On 11 -weighted MR images, metastases were seen as areas of significantly decreased signal intensity (compared with normal liver); on 12-weighted MR images, they appeared as areas of significantly increased signal intensity. The signal intensity of areas of focal fatty infiltration on MR images was equal to or slightly different from the liver signal intensity. The mean values of differences between the signal intensity of metastases and that of liver were -36% On 11 -weighted sequences and +1 32% on 12weighted sequences; these values are significantly different

(p

=

.004:

=

=

AJA:155,

November

MEETING

1990

from

the mean values of differences in focal fatty infiltration +4%, respectively; p < .001). These researchers conclude that MR imaging can differentiate between liver metastases and focal fatty infiltration when CT scans show a hypodense lesion in the liver of a patient with malignant disease.

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(-1 % and

Planning

and

Follow-up

of Hepatic

Surgery

Use of three-dimensional (3-D) CT imaging in preoperative planning for liver tumors was discussed by Pablo Ros (University of Florida College of Medicine, Gainesville). Two surgeons independently reviewed both two-dimensional and 3-D CT scans in 1 0 patients with liver tumors. For locating masses, one surgeon found the 3-D scans superior in all 10 cases, and the other surgeon found the 3-D scans superior in eight of 1 0 cases. For the first surgeon, the 3-D scans indicated a change in therapeutic approach in five cases; for the second, such a change was indicated by 3-D scans in four cases. Both surgeons preferred the 3-D coronal images to the other views; moreover, the 3-D image, especially in the coronal plane, was immediately accepted by the surgeons. With this technique, however, no more than two structures can be reconstructed at one time, real-time rotation capabilities are lacking, and much time is required of the radiologist (70-80 mm/scan). However, 3-D Cl seems to have great potential for liver imaging; not only do surgeons accept the technique and prefer the images to two-dimensional scans, but 3-D CT offers better visualization of central lesions and anatomic orientation. A clinical hematologist, J. P. Kaltwasser (J. W. Goethe University, Frankfurt am Main, West Germany), discussed the possible role of MR imaging in the quantitative determination of liver iron in iron-overload syndromes. In iron storage disease, a progressive increase in total iron produces cellular damage and functional insufficiency of the involved organs. Hereditary hemochromatosis is primary iron-storage disease; acquired hemochromatosis (or secondary iron-storage disease) results from excessive dietary intake of iron. Usually, the liver is the first organ to be affected, and, to date, liver biopsy has been the most helpful clinical test to detect the distribution of iron, the extent of tissue injury, and the iron concentration in the liver. However, in order to find a noninvasive method to measure iron, Dr. Kaltwasser and colleagues studied MR images of 35 patients with various degrees of liver iron overload. To quantitate liver iron overload, they used 1 .0- to 1 .5-1 MR images (12-weighted sequences with very short lEs). Twofindings suggested that MR imaging may be useful in measuring liver iron overload: (1 ) the 12 relaxation rate (1 /12) had a direct and significant correlation (r = .79) with the serum ferritin concentration, and (2) the 12 relaxation rate and liver iron concentration from biopsy specimens (the gold standard) showed a nearly linear correlation (r .90). Another study about the use of MR imaging to measure liver iron overload for surgical planning was presented by Yves Gandon (Pontchaillou Hospital, Rennes, France). Dr. Gandon and colleagues prospectively studied MR images of =

1129

NEWS

the liver in 40 patients with idiopathic hemochromatosis, 10 patients with chronic liver disease, and 1 0 normal subjects. On a 0.5-1 MR unit, spin-echo, inversion-recovery, and breath-hold gradient-echo sequences were performed. Analyses of the images included regions of interest (ROIs) of signal intensity, calculation of signal-to-noise ratios and tissue ratios (eg., liver to spleen or liver to muscle), and calculation of relaxation times. These values were then correlated with liver iron concentrations (LIC) from liver biopsy, which was performed in all patients. Biopsy results showed that LIC was normal in the 10 patients with chronic liver disease but ranged from 40 to 860 moI/g in patients with hemochromatosis. In spin-echo MR sequences, liver signal-to-noise ratios were significantly lower in hemochromatosis patients than in either chronic liver disease patients or normal subjects; however, there was no significant difference in the signal-to-noise ratios of spleen, fat, or muscle among the three groups. Good correlations (r = .8) were found between LIC values and liverto-spleen ratios and between LIC values and liver-to-muscle ratios, but slight iron overload could not be detected on spinecho images. Gradient-echo 12-weighted sequences were more sensitive to slight iron overload, because such overload significantly decreased liver signal on these images. Also, these sequences provided excellent correlations (r = .85) between LIC values and liver-to-spleen ratios and between LIC values and liver-to-muscle ratios. With the more sensitive sequences, iron concentrations as low as 80 mol/g can be detected by MR imaging. This information and MR-derived estimates of liver volume can aid the surgeon in determining how much iron must be withdrawn.

Special

MR and

CT Techniques

for Liver

Imaging

MR Imaging SIIR MR imaging of focal liver disease was discussed by Albert A. Moss (University of Washington Medical Center, Seattle). Ihe advantages of a short inversion time (TI) include suppression of signal from fat and increased brightness of diseased tissue (and therefore increased contrast between diseased and normal tissue). However, limitations of STIR imaging include the equal brightness of tumor and edema, as well as the low signal-to-noise ratio, small number of slices per unit time, and low spatial resolution on SIIR compared with spin-echo sequences. Dr. Moss and colleagues used a 1 5-T MR imager to study 41 proved liver lesions; they performed both STIR and double-echo spin-echo examinations. Three radiologists blindly evaluated both the SIIR and spin-echo images for several factors, including presence of lesion, subjective lesion conspicuity, and lesion volume. All 41 lesions were seen clearly on STIR images; three lesions were missed on spin-echo images. STIR images were judged to provide better conspicuity in 66% of cases; lesion conspicuity was about equal in the other 34%. Lesion volume determinations by the two methods were within 20% of each other in 66% of the lesions; in 34%, the tumor volume measurement was larger on STIR than on spin-echo images. STIR can be a valuable adjunctive technique for liver imaging

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1130

MEETING

because the slightly higher lesion conspicuity on STIR can be helpful in showing lesions to a referring physician, the extent of abnormality and number of lesions can be judged more accurately with STIR, and because of STIR’s higher sensitivity, a radiologist can have greater confidence in judging a study to be normal. Joseph K. 1. Lee(Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO) discussed the phase-contrast technique of proton-spectroscopic MR imaging (PSI), which is also called chemical-shift imaging. A modification of the conventional spin-echo technique, phase-contrast PSI can produce-within less than 30 mmseparate water and fat images with good spatial resolution. Dr. Lee reported that, in finding small fatty changes in the liver, out-of-phase (opposed) PSI is more sensitive than the conventional in-phase spin-echo imaging (with any echo time); PSI actually triples the difference between normal and fatty liver. Using a 0.5-I MR imager, these researchers compared images generated by 11 - and 12-weighted PSI and spin-echo sequences for detecting liver metastases. In 24 patients, 11weighted spin-echo images were better than 12-weighted PSI at showing the correct number of metastases in seven cases and at lesion conspicuity in 1 1 cases (the two methods were about equivalent in all other cases). In 27 patients, 12weighted sequences for the two methods were compared; in counting of lesions and lesion conspicuity, 12-weighted PSI was better than 12-weighted spin-echo imaging in six and 12 cases, respectively (the two methods were about equivalent in almost all other cases). Iherefore, the short-IR, short-TE spin echo sequence is the preferred method of lesion detection. For detecting fatty infiltration of the liver, 12-weighted PSI is preferred. Dr. Lee noted that PSI is most useful in determining the cause of focal low-attenuation lesions detected by CT. The use of MR spectroscopy for differential diagnosis of liver tumors was the topic of a lecture given by Gary M. Glazer (Stanford University School of Medicine, Stanford, CA). The current limitations of 31P MR spectroscopy include crude localization schemes, uncontrolled variability in histologic grades of tumors, and variability in the morphology of liver tumors. However, MR spectroscopy of tumorous tissue does differ from that of normal hepatic parenchyma: for tumors, phosphomonoester (PME) and phosphodiester (PDE) peaks are usually elevated relative to either the inorganic phosphate (P1) or a beta-adenosine triphosphate(fl-AIP) peak. Dr. Glazer and colleagues used MR spectroscopy to evaluate 31 patients with liver metastases, eight patients with hepatomas, eight patients with hemangiomas, and five normal volunteers. Imaging parameters included use of a 8- to 1 4-cm surface coil over the lesion; proton shimming, and an average total acquisition time of 21 mm 25 sec. Spectral quantitation parameters included operator-selected peak heights, peak areas via operator-selected border-to-border integration, and automatic curve-fitting with commercially available software. Dr. Glazer noted that spectral analysis is a crude estimation of the percentage of the spectral slice occupied by the tumor; at this point, there is always the question of how much the diseased tissue is “contaminated” by surrounding normal tissue. The peak-height PME/peak-height 3-AlP ratios for

NEWS

AJR:1 55, November

1990

the metastases and hepatoma groups comprising more than 50% of the spectral slice were significantly different from those ratios in the control subjects: normal subjects, 0.8262; patients with metastases, 2.1 020 (p < .001 ); patients with hepatomas, 1 .8034 (p < .002). A significant overlap was found between the spectral patterns of normal subjects and patients whose tumors occupied less than 50% of the spectral slice; this overlap is a limitation of the MR spectroscopic analysis and reflects the need for better localization methods. No significant difference was found among the spectral patterns of tumors of different malignant histologies. However, the most significant finding was a difference in spectra between hemangiomas and metastases in the calculation of the signal-to-noise ratio using 3-ATP resonance (0.99 for hemangiomas compared with 5.99 for metastases; p < .001 ); this distinctive feature is important because the MR imaging features of hemangioma overlap those of metastases. Yuji Yuasa (Keio University, Tokyo, Japan) discussed MR angiography of the hepatic vein and portal system. The mdications for MR angiography of the upper abdomen include hepatobiliary and renal lesions; stenosis of portal, hepatic, and/or renal veins; and anatomic evaluation of portal or hepatic veins (especially for preoperative evaluation of neoplasms). Dr. Yuasa and colleagues used two-dimensional time-of-flight MR angiography to study 28 cases of liver disease (including 1 5 of hepatocellular carcinoma) and seven cases of biliary tract disease. MR angiography clearly showed venous obstruction in 1 2 of 1 5 cases of hepatocellular carcinoma. Not only did the results of MR angiography correlate well with the results of conventional angiography, but MR angiography also eliminated the problem of the superimposition of great vessels onto the portal and hepatic venous system and provided good visualization of organ contours (which was further improved with frequency-selective presaturation). Three researchers presented studies on fast MR imaging techniques. Akihiro Tanimoto (Keio University Hospital, Tokyo, Japan) reported a study of a fast gradient-echo MR technique: spoiled gradient-recalled acquisition into steady state (spoiled GRASS or SPGR). SPGR was used to evaluate 50 patients (30 hepatomas, 1 0 hemangiomas, and 1 0 metastases). Dr. Tanimoto and colleagues compared images from conventional, spin-echo 11 - and 12-weighted sequences; a fast 11 -weighted sequence; and a 11 -weighted SPGR sequence. Tumor-to-liver contrast-to-noise ratios were significantly higher on SPGR images than on fast and conventional 11 -weighted images. Detectability rates were as follows for hepatocellular carcinomas smaller than or larger than 2 cm, respectively: conventional 11 -weighted, 83% and 83%; conventional 12-weighted, 83% and 1 00%; fast 11 -weighted, 91% and 83%; and SPGR, 100% and 100%. Scott A. Mirowitz (Mallinckrodt Institute of Radiology, Washington University School of Medicine, St. Louis, MO) discussed a study of contrast-enhanced fast MR imaging. Rapid-acquisition spin-echo (RASE) MR images were obtamed in 24 patients with liver lesions (total number of lesions, 62; size range of lesions, 1 -1 5 cm). Four MR methods were used-conventional 12-weighted, conventional 11 -weighted, and highly Ti -weighted RASE-both before and after rapid

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AJR:1 55, November

MEETING

1990

IV administration of gadopentetate dimeglumine. Both the contrast-to-noise and the contrast-to-artifact ratios were significantly higher on RASE images than on other images (p < .05), and both ratios are maximal immediately after injection of the contrast bolus. For example, contrast-to-artifact ratios were 2.7 on contrast-enhanced RASE sequences, 1 .7 on unenhanced RASE sequences, 1.1 on conventional 12weighted sequences, and 1 .0 on conventional 11 -weighted sequences. In this study, enhanced RASE imaging was used to screen the whole liver in less than 5 mm with better lesion conspicuity than any other method. Magnetization-prepared rapid gradient-echo (MP-RAGE) MR imaging of the liver was discussed by Eduard E. de Lange (University of Virginia Health Sciences Center, Charlottesville). Characterized by a rapid gradient-echo sequence preceded by magnetization-preparation pulses to provide Ti - and 12weighted tissue contrast, MP-RAGE MR imaging allows acquisition times of less than 1 sec and provides images that have virtually no motion artifacts. Four imaging studies were evaluated in 1 5 patients with liver lesions: 11 -weighted MPRAGE, 12-weighted MP-RAGE, 11 -weighted spin-echo, and 12-weighted spin-echo sequences. The contrast-to-noise ratios, normalized for voxel volume and imaging time per slice, were significantly higher for Ti-weighted MP-RAGE sequences than for any other sequence (p < .01); moreover, respiratory motion artifacts clearly evident on the spin-echo sequences were not noticeable on MP-RAGE images. These researchers are now developing and testing a 3-D technique for MP-RAGE MR imaging to evaluate the liver for focal disease.

CT Techniques Ruth Langer (Free University of Berlin, Berlin, West Germany) reported the use of subsecond dynamic CT in 42 patients with malignant liver tumors (metastatic lesions, 20two hypervascularized; hepatocellular carcinomas, 1 1 ; bile duct carcinomas, eight; gallbladder carcinomas, three). The examination protocol included a 0.7- to 1 .0-sec scanning time, a 1 - to 2-sec interscan delay, and computer-triggered injection of contrast material beginning 1 0 sec before the start of scanning. No studies were judged to be nondiagnostic; in 90%, image quality was excellent, and in the other 10%, image quality was good. In the arterial phase, 1 2 tumors (10 hepatocellular carcinomas and two metastases) appeared less dense than the normal liver, and 30 (1 8 metastases, 11 bile duct or gallbladder carcinomas, one hepatocellular carcinoma) appeared more dense than liver. A statistically significant difference (p < .05) was found when time-to-peak enhancement (I) and maximal contrast enhancement (D) of hepatocellular carcinomas were compared with those values for bile duct and gallbladder carcinomas (for hepatocellular carcinomas, I 0.33 ± 0.2 and D = 1 .2 ± 0.4; for bile duct and gallbladder carcinomas, I = 31 ± 1 .8 and D 0.7 ± 0.2). A great variability occurred in the I and D values for metastases (I = 2.3 ± 2.7 and D = 0.55 ± 0.3); this variability may be due to the heterogeneity of the primary malignant tumors. These researchers concluded that single-level, sub=

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second dynamic CT can help differentiate hepatocellular carcinomas from bile duct and gallbladder carcinomas; it cannot, however, distinguish hypervascularized metastases from either hepatocellular carcinomas or bile duct/gallbladder tumors. In another study of fast, single-level dynamic Cl, J. Gaa and colleagues (Municipal Hospital, Darmstadt, West Germany) studied 33 patients who had 38 liver hemangiomas (size range, 0.7-1 2.0 cm). Their Cl technique included a 1sec scanning speed and a bolus injection of 1 mI/kg of 30% nonionic contrast material. Ihirty of the hemangiomas (all