Temporal-lobe epilepsy: comparison of CT and MR imaging

In 50 patients with temporal-lobe epilepsy, CT and MR findings were compared. Axial CT scans were obtained before and after administration of contrast material. Coronal MR imaging was carried out with two spin-echo (SE) sequences with a repetition time of 1600 msec and echo times of 35 or 70 msec (SE 1600/35, SE 1600/70). A focal lesion was detected by CT in 12 cases and by MR in 16 cases. If discrete attenuation or signal abnormalities are also taken into account, CT provided a positive finding in 13 cases and MR imaging in 20 cases. With the exception of a small calcification, all the lesions revealed on the CT scans were also detected on the MR images. Among the examinations assessable for temporal-lobe asymmetry, signs of a unilateral reduction in temporal-lobe size were seen on two of 35 CT scans and on 15 of 38 MR images. In three patients who had temporal-lobe resection, a subsequent comparison was made between CT, MR imaging, and pathology. Histologically proven glial reactions that could not be detected on CT were demonstrated as high-signal-intensity lesions on the SE 1600/70 image. We conclude that MR scanning, with its higher sensitivity, superior image quality, and ability of multiplanar imaging, should be the imaging technique of choice in the diagnosis of temporal-lobe epilepsy.     

MR imaging of the acoustic nerves and small acoustic neuromas at 0.6 T: prospective study

To evaluate the capability of magnetic resonance (MR) in imaging normal acoustic nerves, 12 volunteers without signs or symptoms of intracranial disease were examined using a 0.6 T superconductive system. Several spin-echo (SE) pulse sequences were tested to identify the optimal sequence for demonstration of the acoustic nerve bundle. Repetition times (TRs) varied from 300 to 2000 msec and echo times (TEs) from 30 to 120 msec. A single-slice technique was used with 5 and 8 mm sections, one or two data acquisitions per projection, and axial and coronal imaging. The normal acoustic nerves were demonstrated readily by MR in axial and/or coronal sections. The distal parts of the nerves and tumors were imaged best with SE 1500/60. The medial extremities of the seventh and eighth nerves tended to be obscured in this sequence by brightening the cerebrospinal fluid signal adjacent to the brainstem, but they were demonstrated clearly with 500 or 800 msec TR and 30 msec TE. Five patients were studied who had hearing loss and evidence of retrocochlear disease. In four patients, MR imaging demonstrated five acoustic nerve tumors ranging in size from purely intracanalicular to a 12 mm cisternal component. In the fifth case, no tumor was identified by MR imaging or gas computed tomographic (CT) cisternography. Contrast-enhanced CT using a Siemens Somatom DR 3 or GE CT/T 8800 scanner failed to provide convincing evidence of tumor in any case, while gas CT cisternography was positive in all five tumors. All five acoustic neuromas were identified readily using the SE sequences that proved optimal for demonstration of normal nerves. This experience revealed that MR imaging can demonstrate the eighth nerve complex well and reliably. Single-slice (5 or 8 mm) technique is adequate, but multislice without tissue gaps (used recently) is more efficient. Small, even intracanalicular, acoustic neuromas are imaged effectively, indicating that the method is capable of superseding contrast CT cisternography, particularly with improving technology.     

Central nervous system tumors in children: detection by magnetic resonance imaging

Fifty-one pediatric patients who were suspected of having central nervous system (CNS) tumors underwent magnetic resonance (MR) imaging using a 0.35 T Diasonics MT/S system. Pulse intervals (TR) ranged from 0.5 to 2.0 seconds with echo delays (TE) of 28 and 56 msec. The ability of MR and contrast-enhanced CT to detect focal lesions, determine lesion extent, and evaluate associated abnormalities was compared. In most patients in whom there was suspected spinal cord disease, comparison with myelography was made. Thirty-three intracranial lesions were detected with at least one imaging modality in 43 cranial examinations. MR was judged superior to CT in 14 of these cases and CT superior to MR in only one. Of eight spinal examinations, there were six that demonstrated abnormal findings. MR was superior to CT in all six cases and better than myelography in four of five cases where myelography was performed. Spin echo (SE) sequences with long pulse intervals were the most sensitive, but in some cases short pulse intervals permitted further characterization of the lesion. Patient motion was not a problem; sedation was routinely used in children younger than five years of age. MR imaging has rapidly become a valuable diagnostic modality in neuroradiology. The lack of ionizing radiation and the ability to evaluate the spinal cord noninvasively makes it particularly attractive in examination of children.     

Acoustic neuromas: Gd-DTPA enhancement in MR imaging

Magnetic resonance (MR) imaging examinations were performed in ten patients with 12 acoustic neuromas before and after intravenous administration of 0.1 mmol/kg body weight gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA). The degree of enhancement was greatest with the inversion recovery sequence 1,500/500/44 (repetition time [TR]/inversion time/echo delay time [TE]), followed by spin-echo (SE) 544/44 (TR/TE) sequences, then by SE 1,500/44 and SE 1,500/80 sequences. After enhancement there was a 50% reduction for measured T1 values, 33% for T2, and no significant change for proton density. There were no toxic effects on patients. Enhanced CT scans failed to demonstrate lesions in six of 12 cases. Air-CT technique improved sensitivity in four of five cases. Enhanced MR imaging added significant clinical information in two small intracanalicular tumors and in one recurrent tumor.     

Conventional and rapid MR imaging of the liver with Gd-DTPA

Twenty-three patients with malignant hepatic tumors underwent magnetic resonance (MR) imaging before and after intravenous administration of gadolinium-diethylene-triaminepentaacetic acid (DTPA). Two different doses were used, 0.1 mmol/kg and 0.2 mmol/kg. The larger dose proved to be more effective than the smaller dose. The signal-enhancement-to-noise ratio was significantly larger in the tumor than in the liver (2 alpha less than or equal to .05). In a moderately T1-weighted spin echo (SE) sequence (SE 400/30) (repetition time [TR] msec/echo time [TE] msec), the tumor was better defined 6 minutes after administration of Gd-DTPA. More strongly T1-weighted sequences--that is, SE 200/20 and inversion recovery 1,500/35/400 (TR msec/TE msec/inversion time, msec)--showed significantly worse contrast between tumor and liver (signal-difference-to-noise ratio [SD/N]) 10 and 15 minutes after administration (2 alpha less than or equal to .05). On the other hand, the low SD/N in the rapid MR imaging sequence was significantly improved (2 alpha less than or equal to .05). The most important indications for administration of Gd-DTPA in diagnosing hepatic tumors are the presentation of perfusion conditions and contrast optimization in rapid MR images.     

MR imaging of hepatocellular carcinoma

Forty-two patients with hepatocellular carcinoma (HCC) were examined by magnetic resonance (MR) imaging. The presence of tumor was suggested in 41 of 42 cases by a high-intensity area on T2 weighted spin-echo (SE) images with a repetition time (TR) of 1.6 s. Specific findings of HCC such as the presence of a capsule, mosaic pattern, and tumor thrombus in major veins were noted in 10, two, and seven cases, respectively. In six cases the tumor pattern changed from a well-defined mass to an irregular, ill-defined one according to pulse sequence (SE: echo time 35 and 70 ms; TR 1.6 and 0.4 s). In our early experience MR was almost equal to conventional X-ray CT in the detection of main or daughter lesions and in the determination of extent and characterization of HCC.     

Imaging of pancreatic neoplasms: comparison of MR and CT

Thirty-two patients with pathologically proved pancreatic carcinomas or cystadenomas were evaluated with MR images obtained with T1-weighted spin echo (short TR/short TE), inversion recovery, and T2-weighted spin-echo (long TR/long TE) pulse sequences. CT was used as the reference standard to determine the ability of MR to delineate normal and abnormal pancreatic anatomy and thereby to exclude or detect pancreatic malignancy. Short TR/short TE spin-echo sequences were significantly better (p less than .05) than inversion recovery or T2-weighted spin-echo sequences in resolution of both normal and abnormal anatomy. Resolution of pancreatic anatomy correlated (r = .9) with the image signal-to-noise ratio. In seven (22%) of 32 cases, MR visualized pancreatic tumors better than CT did because it showed a signal intensity difference between the tumor and normal pancreatic tissue. Overall, the slight superiority of MR over CT for tumor visualization tended to occur in larger tumors and was not statistically significant. On T1-weighted images, 63% (20 of 32) of pancreatic tumors studied had lower signal intensities than normal pancreatic tissue, whereas on T2-weighted sequences (TE = 60, 120, and 180 msec) only 41% (13 of 32) of tumors had increased signal intensities. Currently available MR imaging techniques offer no significant advantages over CT for evaluating the pancreas for neoplasia.     

Hepatic metastases: randomized, controlled comparison of detection with MR imaging and CT

To determine the accuracy of magnetic resonance (MR) imaging relative to computed tomography (CT) in the diagnosis of liver metastases, a randomized, controlled study was conducted of 135 subjects, including 57 with cancer metastatic to the liver, 27 with benign cysts or hemangiomas, and 51 without focal liver disease. The sensitivity of MR imaging for detecting individual metastatic deposits was 64%, significantly greater than 51% for CT (P less than .001); the difference in sensitivity for identifying patients with one or more hepatic metastases was less (82% for MR imaging vs. 80% for CT). In patients without hepatic metastases, the specificity of MR imaging was 99% versus 94% for CT. Significant differences were found between individual MR pulse sequences in detection of individual lesions. The sensitivity of both T1-weighted spin-echo (SE) (64%) and inversion-recovery (IR) (65%) pulse sequences was significantly (P less than .001) greater than either the TE (echo time) 60 msec (43%) or TE 120 msec (43%) T2-weighted pulse sequences. Overall, the accuracy of a single T1-weighted (10-minute) pulse sequence was superior to that of contrast-enhanced CT.     

Chest-wall invasion by carcinoma of the lung: detection by MR imaging

Nineteen patients with bronchogenic carcinoma were studied by MR imaging to determine the presence of chest-wall invasion. All studies were carried out at 1.5 T, and the results were correlated with chest radiographs or CT scans. All MR studies were interpreted before surgery (13 cases) and without knowledge of the results of other radiologic studies. MR findings indicative of chest-wall invasion included a high-signal focus within the chest wall and/or chest-wall thickening with increased signal on spin-echo (SE) images having a repetition time of 2500 msec and an echo time of 50-100 msec (SE 2500/50-100). In one case, noncontour-deforming high-signal intensity within chest-wall musculature (but no other abnormality) was demonstrated on SE 2500/50-100 images. Coronal or sagittal imaging facilitated identification of tumor contiguity with extrathoracic structures in apical lesions. Contrast differences between normal and invaded chest wall on T2-weighted images were the most helpful in assessing chest-wall involvement. These preliminary observations indicate that MR imaging is useful in the evaluation of chest-wall invasion by carcinoma of the lung.     

MR imaging of brainstem tumors

Eighteen patients aged 4-72 years old with brainstem tumors were studied using a 0.5 T magnetic resonance (MR) imager and a third- or fourth-generation computed tomographic (CT) scanner. MR imaging showed the brainstem to be enlarged on sagittal views in all cases; exophytic growth was seen in eight. Alterations of signal intensities were shown in most cases on spin-echo sequences using 30 and 90 msec echo times and inversion recovery techniques. It was not possible to distinguish primary from metastatic tumors. The configurations and margins of the areas with abnormal signal did not appear to correlate with the clinical behavior of the tumors. CT was able to recognize brainstem tumor in only 13 of 16 cases. In the two cases of metastases, plain CT scans were normal, but enhancement was seen after administration of contrast material in one. It appears that MR imaging is sensitive in detecting tumor enlargement and abnormal signals and is superior to CT in evaluating brainstem tumors.     

Neck neoplasms: MR imaging. Part I. Initial evaluation

Untreated neoplasms of the neck (tumors of the oropharynx, supraglottic area, carotid body, and thyroid, in addition to malignant lymphadenopathy) were evaluated in 23 patients with magnetic resonance (MR) imaging. The results were compared with computed tomographic (CT) scans in 20 patients. Contrast between tumor and fat was best on relatively T1-weighted images (500/30-35 [TR msec/TE msec]), whereas separation of tumor and muscle was best with relatively T2-weighted pulse sequences (1,500/90). Balanced images (1,500/30-35) provided best overall image quality and best demonstrated vascular anatomy. MR imaging was usually superior to CT in showing the relationship of tumor mass to muscle. MR imaging and contrast material-enhanced CT were equivalent in most patients in defining vascular anatomy, but MR imaging was superior when intravenous contrast material was not administered. However, CT was more helpful in showing bone and cartilage anatomy, and in some patients CT also was better in showing airway abnormalities. Despite these limitations, MR imaging is a promising imaging technique for studying neoplasms of the neck.     

Fibrolamellar hepatocellular carcinoma: imaging and pathologic findings in 31 recent cases.

PURPOSE: To review characteristic findings of fibrolamellar hepatocellular carcinoma (HCC) at computed tomography (CT) and magnetic resonance (MR) imaging. MATERIALS AND METHODS: The authors retrospectively reviewed the clinical, pathologic, and preoperative imaging findings in 31 patients with histologically proved fibrolamellar HCC. Dynamic contrast material-enhanced CT of the liver was performed in 31 patients, helical multiphase CT in 21, and MR imaging in 11. Complete resection was performed in 17 patients, and imaging-pathologic correlation was performed. RESULTS: Large tumors (mean diameter, 13 cm) were depicted at CT and MR in all cases. At CT, the margins of the tumors were well defined in 24 (77%) of 31 cases calcifications were depicted in 21 (68%), a central scar in 22 (71%), and abdominal lymphadenopathy in 20 (65%). In 20 (80%) of 25 cases with hepatic arterial phase CT images, all tumors were heterogeneous and depicted areas of hypervascularity. At MR imaging, tumors were hypointense to liver on T1-weighted images (n = 11) and hyperintense to liver on T2-weighted images (n = 10). Calcification was not depicted on MR images, but a central scar was depicted as hypointense to surrounding tumor in nine cases. CONCLUSION: CT and MR images demonstrate characteristic features that may allow confident diagnosis of fibrolamellar HCC.     

STIR MR imaging of the orbit

Fifteen patients with CT-documented orbital lesions were evaluated with MR imaging at 1.5 T with both conventional spin-echo (SE) and short inversion time inversion recovery (STIR) sequences. Fat signal was reliably nulled at inversion times of approximately 120-200 msec in all cases, thereby allowing clear detection of all retrobulbar lesions and normal structures on STIR images as markedly hyperintense relative to fat. All lesions were also clearly depicted on SE images; in fact, short repetition time/short echo time SE sequences were at least as useful as STIR images for illustrating anatomic structures and mass lesions, and in a much shorter scanning time. Separation of optic nerve from perioptic subarachnoid space was clear on SE images, but often difficult or impossible on STIR images owing to the relatively high intensity of normal optic nerves on STIR images. The synergism of relaxation prolongation with STIR actually resulted in loss of information, as any ability to separate the effects of T1 from T2 on signal intensity was impossible when STIR was the sole pulse sequence. We believe that more information is obtained with standard SE sequences than with STIR sequences, and therefore SE remains the method of choice for orbital MR imaging.     

STIR MR Imaging of the Orbit

Fifteen patients with CT-documented orbital lesions were evaluated with MR imaging at 1.5 T with both conventional spin-echo (SE) and short inversion time inversion recovery (STIR) sequences. Fat signal was reliably nulled at inversion times of approximately 120–200 msec in all cases, thereby allowing clear detection of all retrobulbar lesions and normal structures on STIR images as markedly hyperintense relative to fat. All lesions were also clearly depicted on SE images; in fact, short repetition time/short echo time SE sequences were at least as useful as STIR images for illustrating anatomic structures and mass lesions, and in a much shorter scanning time. Separation of optic nerve from perioptic subarachnoid space was clear on SE images, but often difficult or impossible on STIR images owing to the relatively high intensity of normal optic nerves on STIR images. The synergism of relaxation prolongation with STIR actually resulted in loss of information, as any ability to separate the effects of T1 from T2 on signal intensity was impossible when STIR was the sole pulse sequence.We believe that more information is obtained with standard SE sequences than with STIR sequences, and therefore SE remains the method of choice for orbital MR imaging.     

Small hepatocellular carcinoma versus small cavernous hemangioma: differentiation with MR imaging at 2.0 T

Eighteen small hepatocellular carcinomas (HCCs) and 38 hemangiomas less than 5 cm in diameter were studied with magnetic resonance (MR) imaging at 2.0 T. Relatively T1-weighted spin-echo (SE) 500/30 (repetition time msec/echo time msec) images and proton-density 2,000/30 images showed nonspecific contrast-to-noise ratios (C/Ns) and intensity ratios in HCCs and hemangiomas. On T2-weighted 2,000/60, 90, 120, 150, and 180 images, hemangiomas had significantly greater C/N and intensity ratios than HCCs (P less than .05). The SE 2,000/180 sequence showed the greatest difference in tumor-liver intensity ratios between small HCCs and hemangiomas, followed by the SE 2,000/150 sequence, but there was no statistically significant difference between the two pulse sequences. However, the SE 2,000/180 sequence is limited in the number of sections obtainable for routine clinical liver imaging. The findings indicate that the SE 2,000/60 sequence is optimal for the detection of small HCCs and hemangiomas and that the SE 2,000/150 sequence is optimal for distinguishing small HCCs from hemangiomas at 2.0 T.     

Transtympanic iontophoresis with a biocompatible paramagnetic solution at MR imaging: experimental feasibility study in rabbits

PURPOSE: To determine the feasibility of transtympanic iontophoresis in experimental animals with a paramagnetic contrast agent at magnetic resonance (MR) imaging. MATERIALS AND METHODS: Optimal MR sequence parameters and appropriate paramagnetic ion concentrations of a water and gadopentetate dimeglumine solution were initially assessed with phantoms. Iontophoresis was performed in left ears of five rabbits after the external auditory canals were filled with a solution of water and gadopentetate dimeglumine of optimal concentration, and right ears were used as controls. Signal-to-structural noise ratio (SSNR) and contrast-to-structural noise ratio (CSNR) were measured by using regions of interest, and the overall image quality was assessed subjectively. RESULTS: Spin-echo (SE) MR sequences were superior to gradient-echo (GRE) MR sequences in terms of SSNR, CSNR, and overall image quality. Highest SSNR and CSNR values were achieved with 2 mmol/L (2 mM) of gadopentetate dimeglumine solution with both SE (repetition time msec/echo time msec, 500/12; flip angle, 90 degrees ) and GRE (300/10; flip angle, 90 degrees ) sequences in both phantoms and animals. The high signal intensity of gadopentetate dimeglumine solution was recognized in middle ears, vestibules, and semicircular canals of all rabbit ears that had undergone iontophoresis and in none of the control ears. CONCLUSION: With the solution of water and gadopentetate dimeglumine, the maximum SSNR and CSNR with both SE and GRE MR imaging sequences were achieved. The solution can be transferred to the middle and inner ear cavities across an intact tympanic membrane by using transtympanic iontophoresis.     

Fast 3D dynamic MR imaging of the liver with MR SmartPrep: comparison with helical CT in detecting hypervascular hepatocellular carcinoma.

Dynamic magnetic resonance (MR) imaging with SmartPrep was compared with dynamic enhanced helical computed tomography (CT) for the detection of hepatocellular carcinoma (HCC). Thirty patients with 49 HCCs were studied. Arterial-phase MR images using with SmartPrep were significantly superior to arterial-phase CT in detecting small lesions (< or = 2 cm) (85.3% vs. 67.6%, P < .05). In addition, in six recurrent tumors after arterial chemoembolization, dynamic MR imaging with MR SmartPrep technique was superior to helical CT in detecting of recurrent tumors.     

Fast MR imaging of liver metastasis using FLASH and FISP--optimal sequences for T1- and T2*-weighted images

This paper deals with a study to obtain the optimal sequence of gradient echo (GE) for T1- and T2*-weighted images similar to T1- and T2-weighted images of spin echo (SE). Two GE sequences, fast low angle shot (FLASH) and fast imaging with steady-state precession (FISP), were performed in 15 cases of liver metastasis in various combination of flip angle (FA), repetition time (TR), and echo time (TE). The optimal combinations were summarized as follows: 1) T1-weighted FLASH image with FA of 40 degrees, TR of 22 msec and TE of 10 msec, 2) T1-weighted FISP image with FA of 70 degrees, TR of 100 msec, TE of 10 msec, 3) both T2*-weighted FLASH and FISP images with FA of 10 degrees, TR of 100 msec and TE of 30 msec. Not only to provide the adequate T1- and T2*-weighted images but also to enable breath-holding MR imaging, GE sequences can optionally take place SE in cases of deteriorated images caused by moving artifacts. Other applications support the re-examination and further detailing when required, conveniently rather in short time.     

MR imaging of the adrenals: correlation with computed tomography

The purpose of this study was to evaluate the role of magnetic resonance (MR) imaging in adrenal disease based on correlative imaging with CT. Fifty lesions in 36 patients with a variety of adrenal diseases were evaluated, at 0.5 T using spin echo (SE) multislice short repetition time (TR) and SE multislice multiecho long TR sequences. It is concluded that MR is capable of identifying most adrenal abnormalities previously detected by CT. The results suggest that MR has a greater specificity for mass lesions and might be useful to differentiate nonfunctioning adenomas from functioning adenomas, metastasis, pheochromocytomas, cysts, and intraadrenal hemorrhage. Magnetic resonance imaging also has the potential to detect aldosteronomas by increased signal intensity in addition to contour distortion using long TR/echo time sequences. The ability to perform multiplanar imaging and the presence of superior contrast as compared with CT are useful for the assessment of origin and extension of large lesions and the detection of pheochromocytomas in complex cases. Considering MR's limitations, we believe that at present its major role in evaluation of adrenal disease should be complementary to CT.     

Breast and axillary tissue MR imaging: correlation of signal intensities and relaxation times with pathologic findings

We tested a variety of inversion-recovery (IR) and spin-echo (SE) sequences by imaging the breast masses of 22 patients before surgery and 23 tissue specimens with magnetic resonance (MR) imaging at 0.6 T to determine the most effective pulse sequences to evaluate breast disease. An SE pulse sequence using a long repetition time (TR) of 1,600 msec and a long echo time (TE) of 90 msec was found to be the most sensitive in depicting carcinoma in the excised tissue specimens, with all of the carcinomas (n = 15) demonstrating irregular areas of higher signal intensity (SI) than that of the adjacent fat. However, only five of 11 breast carcinomas present in the preoperative patients produced a higher SI than that produced by fat on the same T2-weighted sequence. Five of the remaining six carcinomas in the preoperative patients appeared as localized distortions of fibroductular architecture on both T2-weighted SE and IR sequences. In axillary tissue specimens, both metastatic carcinoma and hyperplastic lymph nodes produced a high SI on T2-weighted SE sequences. However, metastatic carcinoma had a significantly longer T2 relaxation time than did hyperplastic lymph nodes.