0895-6111/91 $3.00 + a0 copyright 0 1991 Fwgamon Press plc
Computerized MedicocImoging and Graphics, Vol. 15, NO. 6. pp. 451-454. 1991 Printed in the USA. All rights reserved.
PERIPHERAL FINDINGS IN MR USING SURFACE COIL FutoshiMihara’, SadayukiMurayama’“, KundanL. Gupta’, Nam Lee2** andArvin E. Robinson’ Department of ‘Radiology and ‘Tulane Medical School, Tulane University Medical Center, New Orleans, LA (Received
2 April
1991)
Abstract-Incidental peripheral lesions found during neuroradiological MR examinations with surface coils are reviewed. These include intracranial metastmes during orbital examinations, cerebellar and thyroid lesions during cervical spine examinations, and dissecting and saccular abdominal aneurysms, as well as renal and intrapelvic abnormalities during lumbar spine examinations. Because of the reduced field-of-view and rapid signal drop-off in deeper portions of the body when examinations are performed with surface coils, peripheral and deep regions also need careful attention during routine evaluation.
Key Words: Magnetic resonance, Surface coil, Incidental findings, Orbit, Cervical spine, Lumbar spine vantages of surface coil utilization are summarized in Table 1. A circular surface coil enhances the signal from a hemispheric region which has about the same radius as the surface coil. However, the signal drops off rapidly according to the distance from the surface of the coil. Therefore, the surface coil does not receive a sufficiently strong signal from areas that are deep or peripheral to the portion of interest. Optimal surface coil diameters are calculated by the formulae (3): A) Circular coil Diameter = 2 X $! X Depth of the Lesion (1) B) Rectangular coil (Long side/Short side 1 1.75) Short side length = 2 X Depth of the Lesion (2) Smaller surface coils have stronger signals in shallow regions, but the signal for larger surface coils is stronger in deeper portions.
INTRODUCTION Surface coils are routinely used in MR examination of the orbit, spine, neck, temporomandibular joint, and extremities, whenever the region of interest is near the body surface. Surface coils facilitate MR imaging by increasing the signal-to-noise ratio (S/N ratio) in a local region. This contributes to increased spatial resolution and decreased scan time. With surface coils, the S/N ratio can be improved from four- to tenfold when compared with standard head or body coils (1). However, trade-offs exist such as a reduced field-of-view (FOV) and a nonuniform signal response which decreases substantially toward deeper portions of the body (2). This compromise in anatomic coverage is perhaps the most serious disadvantage of surface coil utilization. Herein, we present our experience with incidentally detected abnormalities in peripheral areas during neuroradiological MR imaging with surface coils. A short review of the basic physical aspects is also included.
CLINICAL
CASES
Orbital examinations When a 5.5-in surface coil is applied in an orbital examination, a better S/N ratio can be obtained in the
BASIC ASPECTS Surface coils facilitate MR imaging by increasing the SIN ratio in a local region. The advantages and disad-
Table 1. Advantages and disadvantagesof surface coil. Advantages Increased S/N ratio Increased spatial resolution Decreased scan time Application to all body surfaces Ease of handling Variable size and shape Low cost
*Current address:Departmentof Radiology,Faculty of Medicine, Kyushu University, Fukuoka 812, Japan. **Current address: Department of Radiology, University of Florida Health Science Center, Jacksonville, FL. Address correspondence to Futoshi Mihara, M.D., University of Maryland Medical System, Department of Diagnostic Radiology, 22 S. Greene Street, Baltimore, MD 21201. 4.51
Disadvantages Reduced field-of-view Nonuniform signal response Increased motion artifacts
452
Computerized
Medical
Imaging
and Graphics
November-December/l991,
Volume
15, Number
6 *
G-4
Fig. 1. A 73-year-old female patient with metastatic tumor in the orbit. (a) Extensive tumor involvement of the right frontal bone is noted on a postcontrast Tl-weighted image with a surface coil (long arrow). However, in deep portions of the image a second ring-enhanced tumor is faintly noted in the right frontal lobe (short arrow). (b) A right frontal lobe metastasis (arrow) from anaplastic carcinoma of the lung is clearly demonstratedwith a head coil.
Fig. 2. A .52-year-oldmale who had undergone a fusion operation at the level of C-5 to C-7. (a) On a sagittal T2weighted image with a surface coil, an area of marked hypointensity is noted in the right cerebellar hemisphere (arrow). (b) On an axial T2-weighted image with a head coil, the lesion shows mixed hypo- and hyperintqmsity,compatible with a cavernoushemangioma (arrow).
Peripheral findings in MR using surface coil l F. MIHARAet al.
Fig . 3. A 50-year-old male with a minimal bulging disc at the level of IA-5. (a) On an axial pmton-density-weighted
imaIge with a surface coil, an intimal flap (arrow) confirms a dissecting aneurysm of the abdominal aorta. (b) On a cononal slice, the intimal flap extends to the left common iliac artery (arows), which is subsequentlyproven by mzW@v.
453
454
Computerized Medical Imaging and Graphics
orbit as deep as the apex. On the other hand, the S/N ratio is much better in deeper portions when a standard head coil is used. When studying oribital metastatic tumors (Fig. 1) or perioptic nerve meningioma in cases of neurofibromatosis, careful attention is also required for consideration of intracranial involvement. Cervical spine examinations During cervical spine examinations, signals from peripheral and anterior portions of the neck drop off. Cerebellar or thyroid regions also require attention. We recorded cerebellar cavernous hemangiomas (Fig. 2) and thyroid adenomas. Lumbar spine examinations Because the region of interest is elongated in a lumbar spine examination, rectangular surface coils are often used. There are a variety of organs at the peripheral or deep portions of the images. We found abdominal dissecting and saccular aneurysms (Fig. 3), renal cysts, intrapelvic kidneys, uterine fibroids and ovarian cysts. SUMMARY Surface coils increase the S/N ratio by reducing the diameter of the loop and placing it closer to the body. This results in enhanced sensitivity near the coil and decreased signal and noise distally. However, a reduced FOV and a rapid signal drop-off at deeper portions of the body are serious disadvantages in surface coil utilization. When surface coil properties are considered, optimal surface coils should be selected and
November-December/ 199 1, Volume 15, Number 6 .
peripheral and deep regions should be carefully reviewed for unexpected abnormalities.
Acknowledgments-The authors wish to thank Richard Hutton for technical assistance and Terry McGuckin for secretarial assistance.
REFERENCES 1. Lufkin, R.B.; Hanafee, W. Surface coils in magnetic resonance imaging. Applied Radiology 16~66-72; 1987. 2. Kneeland, J.B.; Hyde, J.S. High-resolution MR imaging with local coils. Radiology 171:1-7; 1989. 3. Goshima, H.; Mano, I. MRI surface coils. J. Med. Imaging b(supplement):211-215; 1989. About the Author-FuTosHI MIHARA,M.D., was Research Assistant Professor of Radiology, Tulane University Medical Center (TUMC), New Orleans, LA. He currently serves as Research Assistant Professor of Diagnostic Radiology, University of Maryland Medical System, Baltimore, MD. About the Author--SmAnnu M~JRAYAMA.M.D., was Research Assistant Rrofessor of Radiology, TUMC, and currently on staff of Body Imaging, Kyushu University, Japan.
About the Author--KuNnAn L. GUFTA, M.D., is Associate Professor and Chief of Neuroradiology section of TUMC. About the Author--NM LEE, M.D., is a graduate of TUMC and currently a resident of Radiology, University of Florida Health Science Center, Jacksonville, FL. About the Author-hvm E. ROBINSON,M.D., is Chairman and Professor of Radiology of TUMC.
Computerized MedicocImoging and Graphics, Vol. 15, NO. 6. pp. 451-454. 1991 Printed in the USA. All rights reserved.
PERIPHERAL FINDINGS IN MR USING SURFACE COIL FutoshiMihara’, SadayukiMurayama’“, KundanL. Gupta’, Nam Lee2** andArvin E. Robinson’ Department of ‘Radiology and ‘Tulane Medical School, Tulane University Medical Center, New Orleans, LA (Received
2 April
1991)
Abstract-Incidental peripheral lesions found during neuroradiological MR examinations with surface coils are reviewed. These include intracranial metastmes during orbital examinations, cerebellar and thyroid lesions during cervical spine examinations, and dissecting and saccular abdominal aneurysms, as well as renal and intrapelvic abnormalities during lumbar spine examinations. Because of the reduced field-of-view and rapid signal drop-off in deeper portions of the body when examinations are performed with surface coils, peripheral and deep regions also need careful attention during routine evaluation.
Key Words: Magnetic resonance, Surface coil, Incidental findings, Orbit, Cervical spine, Lumbar spine vantages of surface coil utilization are summarized in Table 1. A circular surface coil enhances the signal from a hemispheric region which has about the same radius as the surface coil. However, the signal drops off rapidly according to the distance from the surface of the coil. Therefore, the surface coil does not receive a sufficiently strong signal from areas that are deep or peripheral to the portion of interest. Optimal surface coil diameters are calculated by the formulae (3): A) Circular coil Diameter = 2 X $! X Depth of the Lesion (1) B) Rectangular coil (Long side/Short side 1 1.75) Short side length = 2 X Depth of the Lesion (2) Smaller surface coils have stronger signals in shallow regions, but the signal for larger surface coils is stronger in deeper portions.
INTRODUCTION Surface coils are routinely used in MR examination of the orbit, spine, neck, temporomandibular joint, and extremities, whenever the region of interest is near the body surface. Surface coils facilitate MR imaging by increasing the signal-to-noise ratio (S/N ratio) in a local region. This contributes to increased spatial resolution and decreased scan time. With surface coils, the S/N ratio can be improved from four- to tenfold when compared with standard head or body coils (1). However, trade-offs exist such as a reduced field-of-view (FOV) and a nonuniform signal response which decreases substantially toward deeper portions of the body (2). This compromise in anatomic coverage is perhaps the most serious disadvantage of surface coil utilization. Herein, we present our experience with incidentally detected abnormalities in peripheral areas during neuroradiological MR imaging with surface coils. A short review of the basic physical aspects is also included.
CLINICAL
CASES
Orbital examinations When a 5.5-in surface coil is applied in an orbital examination, a better S/N ratio can be obtained in the
BASIC ASPECTS Surface coils facilitate MR imaging by increasing the SIN ratio in a local region. The advantages and disad-
Table 1. Advantages and disadvantagesof surface coil. Advantages Increased S/N ratio Increased spatial resolution Decreased scan time Application to all body surfaces Ease of handling Variable size and shape Low cost
*Current address:Departmentof Radiology,Faculty of Medicine, Kyushu University, Fukuoka 812, Japan. **Current address: Department of Radiology, University of Florida Health Science Center, Jacksonville, FL. Address correspondence to Futoshi Mihara, M.D., University of Maryland Medical System, Department of Diagnostic Radiology, 22 S. Greene Street, Baltimore, MD 21201. 4.51
Disadvantages Reduced field-of-view Nonuniform signal response Increased motion artifacts
452
Computerized
Medical
Imaging
and Graphics
November-December/l991,
Volume
15, Number
6 *
G-4
Fig. 1. A 73-year-old female patient with metastatic tumor in the orbit. (a) Extensive tumor involvement of the right frontal bone is noted on a postcontrast Tl-weighted image with a surface coil (long arrow). However, in deep portions of the image a second ring-enhanced tumor is faintly noted in the right frontal lobe (short arrow). (b) A right frontal lobe metastasis (arrow) from anaplastic carcinoma of the lung is clearly demonstratedwith a head coil.
Fig. 2. A .52-year-oldmale who had undergone a fusion operation at the level of C-5 to C-7. (a) On a sagittal T2weighted image with a surface coil, an area of marked hypointensity is noted in the right cerebellar hemisphere (arrow). (b) On an axial T2-weighted image with a head coil, the lesion shows mixed hypo- and hyperintqmsity,compatible with a cavernoushemangioma (arrow).
Peripheral findings in MR using surface coil l F. MIHARAet al.
Fig . 3. A 50-year-old male with a minimal bulging disc at the level of IA-5. (a) On an axial pmton-density-weighted
imaIge with a surface coil, an intimal flap (arrow) confirms a dissecting aneurysm of the abdominal aorta. (b) On a cononal slice, the intimal flap extends to the left common iliac artery (arows), which is subsequentlyproven by mzW@v.
453
454
Computerized Medical Imaging and Graphics
orbit as deep as the apex. On the other hand, the S/N ratio is much better in deeper portions when a standard head coil is used. When studying oribital metastatic tumors (Fig. 1) or perioptic nerve meningioma in cases of neurofibromatosis, careful attention is also required for consideration of intracranial involvement. Cervical spine examinations During cervical spine examinations, signals from peripheral and anterior portions of the neck drop off. Cerebellar or thyroid regions also require attention. We recorded cerebellar cavernous hemangiomas (Fig. 2) and thyroid adenomas. Lumbar spine examinations Because the region of interest is elongated in a lumbar spine examination, rectangular surface coils are often used. There are a variety of organs at the peripheral or deep portions of the images. We found abdominal dissecting and saccular aneurysms (Fig. 3), renal cysts, intrapelvic kidneys, uterine fibroids and ovarian cysts. SUMMARY Surface coils increase the S/N ratio by reducing the diameter of the loop and placing it closer to the body. This results in enhanced sensitivity near the coil and decreased signal and noise distally. However, a reduced FOV and a rapid signal drop-off at deeper portions of the body are serious disadvantages in surface coil utilization. When surface coil properties are considered, optimal surface coils should be selected and
November-December/ 199 1, Volume 15, Number 6 .
peripheral and deep regions should be carefully reviewed for unexpected abnormalities.
Acknowledgments-The authors wish to thank Richard Hutton for technical assistance and Terry McGuckin for secretarial assistance.
REFERENCES 1. Lufkin, R.B.; Hanafee, W. Surface coils in magnetic resonance imaging. Applied Radiology 16~66-72; 1987. 2. Kneeland, J.B.; Hyde, J.S. High-resolution MR imaging with local coils. Radiology 171:1-7; 1989. 3. Goshima, H.; Mano, I. MRI surface coils. J. Med. Imaging b(supplement):211-215; 1989. About the Author-FuTosHI MIHARA,M.D., was Research Assistant Professor of Radiology, Tulane University Medical Center (TUMC), New Orleans, LA. He currently serves as Research Assistant Professor of Diagnostic Radiology, University of Maryland Medical System, Baltimore, MD. About the Author--SmAnnu M~JRAYAMA.M.D., was Research Assistant Rrofessor of Radiology, TUMC, and currently on staff of Body Imaging, Kyushu University, Japan.
About the Author--KuNnAn L. GUFTA, M.D., is Associate Professor and Chief of Neuroradiology section of TUMC. About the Author--NM LEE, M.D., is a graduate of TUMC and currently a resident of Radiology, University of Florida Health Science Center, Jacksonville, FL. About the Author-hvm E. ROBINSON,M.D., is Chairman and Professor of Radiology of TUMC.
