Comparison of GRASE and Turbo Spin Echo Sequences in Brain MR Imaging

PURPOSE: The purpose of this study was to evaluate the utility of GRASE images of the brain, which combinegradient echo-EPI and turbo spin echo, and to compare the results with those of the turbo spin echo (TSE)technique. MATERIALS AND METHODS: We analyzed and compared brain MR images obtained in 25 patients betweenOctober, 1996 and January, 1997, both TSE and GRASE techniques. Diagnosis was normal (n=5), infarct orischemia(n=10), intracerebral hemorrhage(n=6), and neoplasm(n=4). TSE and GRASE MR images were obtained using a1.5T Gyroscan ACS-NT(Philips, Netherlands). For qualitative assessment, overall image quality, discriminationbetween cortical gray-white matter and basal ganglia-white matter, lesion conspicuity, and MR artifact wereevaluated using a subjective grading system ranging from 1 to 5(1=TSE better than GRASE, 5=GRASE better than TSE).For quantitative assessment, signal-to nosise ratios (SNRs) were calculated for cortical gray matter, whitematter, basal ganglia, and lesions, and contrast-to nosise ratios (CNRs) were calculated for cortical gray-whitematter, basal ganglia-white matter and lesions-white matter, We measured image acquisition time and RF specificabsorption rate (SAR) on TSE and GRASE. RESULTS: Qualitative assessment showed that overall image quality,discrimination between cortical gray-white matter and basal ganglia-white matter, and lesion conspicuity were notsignificantly different between the two imaging techniques. MR artifact was more frequently seen on GRASE than onTSE. Quantitative assessment showed that the SNR of each brain tissue and lesion was significantly greater on TSEimages than on GRASE. Cortical gray-white matter and basal ganglia-white matter CNRs were significantly greater onGRASE images than on TSE, but lesion-white matter CNR was not significantly different between the two techniques.Image acquisition time was 3 minute 31 second in TSE and 1 minute 12 second in GRASE. SAR was lower in GRASE thanin TSE. CONCLUSION: With regard to MR artifact, GRASE is more sensitive than TSE, but as regards image qualityand lesion distinction, the two modalities show no distinct difference. Since GRASE is superior to TSE for thedetection of hemosiderin, and image acquisition time is three times shorter using GRASE, GRASE might usefully beapplied during the evaluation by MR imaging of certain brain conditions.

CT and MR Findings of Parotid Masses: Benign versus Malignant

PURPOSE: To determine the differential findings of benign and malignant parotid masses, as seen on CT and MRimaging. MATERIALS AND METHODS: The CT(24 cases of benign and 10 cases of malignant masses) and MR imaging(18cases of benign and 9 cases of malignant masses) findings of parotid gland masses confirmed by surgery orhistopathology were analyzed by two radiologists ; they focused on size, cystic change, the presence ofcalcification within the mass, density or signal intensity and margin, degree of contrast enhancement andhomogeneity, location and bilaterality, associated findings-including infiltration into surrounding structures andlymphadenopathy. RESULTS: In one of the 34 cases seen on CT, precontrast images were not available. In 15 of 23benign cases(65.2%), the density of the mass, as seen on pre-contrast enhanced CT scan, was lower than that ofmuscle. In ten malignant cases, density lower than that of muscle was noted in only two cases (20%). OnT2-weighted images, low signal intensity to fat was noted in five of nine cases(55.5%) of malignant lesion, but inno cases involving benign parotid masses. On CT scanning, an indistinct margin of the masses was observed in fiveof 24 benign cases(20.8%) and three of ten malignant cases(30%), but on MR imaging, this was seen in three of 18benign cases(16.7%) and 6 of 9 malignant cases(66.7%). On pre-contrast enhanced CT scan, 15 of 23 benign casesshowed homogenous density, but 12 of these 15 (80%) changed to inhomogenous on post-contrast enhanced CT scan.Among the 12, pleomorphic adenoma accounted for ten cases(83.3%). On CT scanning, infiltration into surroundingstructures including subcutaneous fat tissue was observed in three of 24 benign cases(12.5%) and four of tenmalignant cases(40.0%) ; and on MR imaging, in one of 18 benign cases(5.5%) and six of nine malignantcases(66.7%). CONCLUSION: If a mass of lower attenuation than that of muscle is seen on pre-contrast enhanced CTscan, or density patterns change from homogenous on pre-contrast CT to inhomogenous on post-contrast CT scan, themass may be benign. However, for the differential diagnosis of benign and malignant parotid masses, the margin ofthe mass is not helpful. Masses which on T2-weighted MR images show an indistinct margin, lower signal intensityto fat and infiltration into surrounding structure are more likely to be malignant. CT and MR findings relating tomass size, cystic change within mass, and lymphadenopathy are not, however, helpful for the differential diagnosisof benign and malignant parotid masses.

Radiologic Evaluation of the Therapeutic Effect of Gamma Knife Radiosurgery in Cerebral Vasular Malformation

PURPOSE: To evaluate the therapeutic effect of gamma knife radiosurgery in cerebral vascular malformationusing a radiologic imaging method such as MRI or angiography. MATERIALS AND METHODS: We retrospectively reviewedMRIs, Ct scans and angiograms of 29 cases of arteriovenous malformation and 15 of cavernous malformation beforeand after gamma knife radiosurgery. The patients underwent follow-up radiologic studies for between 6 and 35months after radiosurgery. No patient underwent ofter surgery of embolization. Radiological imaging analysisfocused on changes in the volume of the nidus or central core. Other findings of edema, cystic change, hemorrhage,signal intensity, enhancement and distributional vascular markings were also studied. The volume of the AVM niduswas measured and assigned ot one of four groups : 4-10cc and> 10cc. RESULTS: In arteriovenousmalformation cases, the volume of the nidus decreased by mean 60.2%; reduction was greatest(68.1%) in the 1-4ccgroup. Three cases showed complete loss of the nidus at 9, 12 and 25 months after radiosurgery, respectively. Innine cases, dereased caliber or loss of draining vein was noted. High signal intensity on T2-weighted MR images,suggesting either edema or demyelination, was observed in four cases. In cavernous angioma cases, core volume wasreduced by 36.8%. Transient cerebral edema and presumed radiation necrosis were observed in two cases and one,respectively. CONCLUSION: Gamma knife suregery was effective in nearly all cases of arteriovenous malformationand some cases of cavernous malformation. More than two years follow-up involving radiologic imaging such as MRIis needed for the evaluation of therapeutic effect and diagnosis of complications.

Radiologic Findings of Intraspinal Epidural Arachnoid Cyst

PURPOSE: To evaluate the radiologic findings of intraspinal epidural arachnoid cyst. MATERIALS AND METHODS: Six pateuts with surgically proven intraspinal epidural arachnoid cyst were included in this study. Four were freeof specific past history, but two had a history of trauma. All underwent examination by plain radiography,CT-myelography and MRI, and the following aspects were retrospectively analysed : vertebral pressure erosion,interpedicular distance, enlargement of neural foramina, as seen on plain radiograph, contrast-filling and lateralbulging of lesions through neural foramina on CT-myelograph, and signal intensity, size and shape of margin andepidural fat pattern, as seen on MRI. RESULTS: Three of four congenital intraspinal epidural arachnoid cysts weresingle in the thoracolumbar region, while in the other case, there were multiple cysts in the mid- and lowerthoracic regions. Cysts were equivaleut in size to between four and six vertebral bodies. Plain radiographicfindings of pedicular pressure erosion, widened interpedicular distance, and bilateral neural foraminalenlargement of several contiguous vertebrae were observed in all four cases. One showed posterior vertebralscalloping. On CT-myelograph, a contrast-filled cystic lesion occupying the posterior epidural space, with lateralbulging through neural foramina and anterior displacement of the contrast-filled thecal sac, was seen. On MRI,longitudinally elongated, well-demarcated cysts were seen to be present in the posterior epidural space; theirsignal intensity was the same as in CSF. An epidural fat cap pattern enveloping the upper and lower ends of thecysts was apparent in all cases. In two cases, traumatic intraspinal epidural arachnoid cysts were situated in thethoracolumbar and lumbosacral region, respectively, near a previously injured region and were smaller (equivalentto the height of three vertebral bodies). CT-myelograph and MRI showed that their effect on the thecal sac wascompressive only. CONCLUSION: When pressure erosion of vertebral odies and pedicles of contiguous severalvertebrae in the thoracic or thoracolumbar region is recognized on plain radiograph, intraspinal epiduralarachnoid cyst should be included in differential diagnosis, and for accurate evaluation, CT-myelograph and/or MRIare needed.