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Show Journal of Neuro- Ophthalmology 20( 2): 135- 137, 2000. © 2000 Lippincott Williams & Wilkins, Inc., Philadelphia 4.0 Tesla Magnetic Resonance Imaging of Brainstem Lesions With Ocular Motility Deficits Victoria S. Pelak, MD, Lizann Bolinger, PhD, Steven L. Galetta, MD, Norman Butler, Alan Stein, and Grant T. Liu, MD The authors studied six patients with brainstem ocular motility deficits with 4.0 Tesla ( T) magnetic resonance imaging to investigate whether a higher field strength would produce superior images compared with 1.5T. In four patients whose lesions were evident on 1.5T, the increased signal- to- noise achieved with 4.0T allowed for better resolution at 1- mm slice thickness than was achieved at the standard 5- mm slice thickness with 1.5T. In the two patients with unremarkable 1.5T scan results, 4.0T also failed to demonstrate a lesion. Therefore, 4.0T imaging has superior resolution to 1.5T imaging and can provide more detailed images of lesions identified by 1,5T. Most clinical magnetic resonance imaging ( MRI) machines use a magnetic field strength of 1.5 Tesla ( T) or less. After the introduction of MRI and spectroscopy with 4.0T systems, ( 1,2) many functional MRI and spectroscopic studies of the human brain have been performed with 4.0T magnets ( 3- 6). However, the clinical utility of MR brain imaging with field strengths greater than 1.5T for other applications is unknown. In a study comparing 4.0T and 1.5T brain images of normal volunteers using manufacturer- provided coils, a 1.3 to 2.3 times increase in signal- to- noise was demonstrated with 4.0T ( 7). This study was performed to compare the quality of 4.0T imaging with 1.5T imaging of brainstem lesions. METHODS 4.0T fast- spin echo MRI studies were performed on five patients with ocular motility deficits 2 days before and 10 days after 1.5T MRI. One patient ( patient 2) had 4.0T imaging two years after the 1.5T MR study. A Manuscript received December 28, 1998; accepted March 23, 2000. From the Division of Neuro- ophthalmology, Departments of Neurology and Ophthalmology ( VSP, SLG, GTL), and the Department of Radiology ( LB, NB, AS), Hospital of the University of Pennsylvania, Philadelphia, Pennsylvania. Presented in part at the North American Neuro- ophthalmological Society meeting, March 1998, Orlando, Florida. Address correspondence to Grant T. Liu, MD, Division of Neuro-ophthalmology, Department of Neurology, Hospital of the University of Pennsylvania, 3400 Spruce Street, Philadelphia, PA 19104. standard 1.5T MR protocol with Tl- and T2- fast spin echo images was used. Before the 4.0T imaging, each patient signed a consent form approved by the University of Pennsylvania Institutional Review Board. Brainstem lesions in patients 1 through 4 were apparent on 1.5T scans. Despite a brainstem localization, no demonstrable lesions were found on routine 1.5T imaging in patients 5 and 6. Patient 1 is a 48- year- old woman with hypertension who presented with a headache, vertigo, intermittent diplopia, and lethargy. On examination, she had a voluntary bilateral horizontal gaze palsy, weakness of the right orbicularis oculi, right facial hemisensory deficit, left hemiparesis, ataxia, and a left hemisensory deficit due to a large pontine hemorrhage. She later exhibited bilateral internuclear ophthalmoplegia. One year later, she was noted to have oculopalatal myoclonus. Patient 2 is a 26- year- old man who developed headache and horizontal diplopia at age 16 due to a ruptured pontine cavernous angioma. At that time, he was treated conservatively and was left with a residual left abduction deficit. Nine years later, he developed a high frequency horizontal pendular nystagmus OS. Patient 3 is a 62- year- old woman who presented with ptosis and diplopia. She had a left third nerve palsy and right hemiataxia ( Claude syndrome) due to a paramedian mesencephalic stroke demonstrated with conventional 1.5T neuroimaging. Patient 4 is a 62- year- old man who was admitted with a new left Horner syndrome, a right hypertropia ( skew deviation), rightward beating nystagmus in right gaze, left dysmetria, gait ataxia, and left face and right arm sensory loss. A left lateral medullary stroke was demonstrated on 1.5T images. Patient 5 is a 55- year- old man with hypertension who was admitted to the hospital for new slurred speech and double vision. He had a leftward conjugate gaze paresis and a left peripheral facial palsy, both of which resolved after 3 days. No brainstem lesions were found on either 1.5T or diffusion- weighted imaging. Patient 6 is a previously healthy 17- year- boy who developed sudden diplopia, dizziness, and difficulty with balance. On examination, he had a bilateral internuclear ophthalmoplegia, upbeat nystagmus, and ataxia. Symp- 755 V. S. PELAK ET AL. FIG. 1. Patient 1. 1.5T and 4.0T brainstem images of a 48- year- old woman who presented with a large pontine hemorrhage. A: 1.5T T2- weighted fast spin echo axial MR image of the pontine hemorrhage ( TR/ TE = 2,700/ 91 ms; FOV = 22 x 16 cm; ma = 256 x 192; slice thickness, 5 mm). B and C: 4.0T images of the same patient demonstrating superior resolution. The margins of the hemorrhage are better defined with 4.0T than with 1.5T. toms resolved spontaneously after 6 weeks. Results of the routine 1.5T images were completely normal and had no white matter lesions. 4.0T imaging parameters, patient' 1; time to recovery/ time to echo ( TR/ TE) = 4,000/ 30 ms; field of view ( FOV) = 20 x 20 cm; matrix ( ma) = 512 x 256; slice thickness, 1 mm. Patients 2 through 6: TR/ TE = 5,000/ 30 ms; FOV = 16 x 16 cm; ma = 512 x 256; slice thickness, 1 mm. Qualitative comparisons between the 1.5T and 4.0T images were made for each patient in terms of resolution of brainstem anatomy and the ability to assess lesions. In patient 2, quantitative comparison of the images were made by calculating the signal- to- noise ratio between 1.5T ( TR/ TE = 2,700/ 96 ms; FOV = 22 x 16 cm; ma = 256 x 192; slice thickness, 5 mm) and 4.0T studies. RESULTS No patient experienced an adverse effect during or after 4.0T imaging. In patients 1 through 4, both 1.5T and 4.0T adequately imaged the brainstem lesions. However, the 4.0T images were superior in qualitative resolution of brainstem anatomy in each patient ( patients 1- 3, Figs. 1- 3; patient 4' s results are not shown). In patient 3, the size and location of the midbrain stroke was inaccurately represented by 1.5T when compared with 4.0T images of the same lesion ( Figs. 3B- D). In patient 2, the ratio of signal- to- noise at 4.0T versus the signal- to- noise at 1.5T was 1.6 in cerebrospinal fluid, 2.3 in cerebral white matter, 1.3 in cortical gray matter, and 1.5 in the red nucleus. DISCUSSION In patients with brainstem lesions associated with ocular motility deficits, 4.0T images had better resolution at 1- mm slice thickness than did 1.5T images at 5- mm slice thickness. The increased signal- to- noise ratio with the 4.0T system allowed for imaging at 1- mm slice thickness. The images produced with a 4.0T system provided better visualization of the fine anatomic detail of the brainstem, including the extraaxial cranial nerves. Lesion size and shape were more accurately assessed with 4.0T imaging due to these factors, as demonstrated in patient 3, in whom a midbrain lesion was incorrectly represented by the 1.5T images. Therefore, with lesions affecting the brainstem, clinical neuroanatomic correlation can be FIG. 2. Patient 2.1.5T and 4.0T images of a 26- year- old man who presented with a ruptured cavernous angioma. A: 1.5T T2- weighted fast spin echo MR images adequately image the hemorrhage. B: 4.0T image of the same patient better demonstrates the heterogenous nature of the lesion. J Neuro- Ophthalmol, Vol. 20, No. 2. 2000 4.0 TESLA MRI OF BRAINSTEM LESIONS 137 ^ y^ fc* ^ m v- ! b FIG. 3. Patient 3. 1.5T and 4. QT images of a 62- year- old woman who presented with a paramedian mesencephalic stroke. A: 1.5T T2- weighted fast spin echo MR image ( TR/ TE = 4,000/ 98 ms; FOV, 22 x 16 cm; ma = 256 x 192; slice thickness, 5 mm) depicting a left paramedian midbrain stroke ( arrow) extending the entire anterior- posterior length of the mesecephalon. B- D: 4.0T images of the same patient revealing that ros-trally, the stroke involves primarily the third nerve fascicle and red nucleus ( arrow in B), but caudally, involvement of the periaqueductal gray region ( arrow in D) is more prominent. more precise with 4.0T MR imaging than with routine 1.5T imaging. This could lead to a better understanding of patient symptoms in certain circumstances. Our results must be tempered by the lack of findings in patients 5 and 6. Clinically, the lesions were localized to the pons, but neither 1.5T nor 4.0T techniques were able to demonstrate a lesion. It is conceivable that pathologically, no lesion was present. However, it is also possible that 4.0T, with the parameters used above, is not more sensitive than 1.5T in detecting brainstem pathology. Therefore, this study demonstrated that 4.0T can offer superior images than those produced by standard 1.5T systems. This was only true in patients 1 through 4, when the lesion had already been identified by 1.5T. In these four patients, the 4.0T images did not provide additional information that affected patient management. The brainstem had been adequately imaged for clinical purposes with the 1.5T magnet. An important future goal is to adjust the 4.0T parameters to allow the detection of clinically significant brainstem lesions not detected by 1.5T imaging. REFERENCES 1. Barfuss H, Fischer MS, Hentschel D, Ladebeck R, Vetter J. Whole- body MR imaging and spectroscopy with a 4- T system. Radiology L988; 169: 8U- 6. 2. Bomsdorf H, Helzel T, Kunz D, Roschmann P, Tschendel O, Wieland J. Spectroscopy and imaging with a 4 tesla whole- body MR system. NMR Biomed 1988; 1: 151- 8. 3. Kim SG, Ashe J, Hendrich K, et al. Functional magnetic resonance imaging of motor cortex: hemispheric asymmetry and handedness. Science 1993; 261: 615- 7. 4. Goodyear BG, Gati JS, Menon RS. The functional scout image: immediate mapping of cortical function at 4 Tesla using receiver phase cycling. Magn Reson Med 1997; 38: 183- 6. 5. Menon RS, Ogawa S, Strupp JP, Ugurbil K. Ocular dominance in human VI demonstrated by functional magnetic resonance imaging. J Neurophysiol 1997; 77: 2780- 7. 6. Langkowski JH, Wieloand J, Bomsforf H, et al. Pre- operative localized in vivo proton spectroscopy in cerebral tumors at 4.0 Tesla-first results. Magn Reson Imag 1989; 7: 547- 55. 7. Bolinger L, Liu GT, Butler N, Lexa F. Thin slice, high resolution imaging of the brain at 4T ( abstract). Sydney: International Society of Magnetic Resonance in Medicine, 1998. J Neuro- Ophthalmol, Vol. 20, No. 2, 2000 |
