Usefulness of Post-enhanced Delayed FLAIR Imaging for Making the Diagnosis of Leptomeningitis

PURPOSE: To evaluate the usefulness of post-enhanced delayed FLAIR (fluid-attenuated inversion-recovery) images in the diagnosis of leptomeningitis. MATERIALS AND METHODS: We obtained the pre- and post-enhanced FLAIR images of 7 rabbits every hour after infusing triple doses of contrast, and we measured the signal intensities of the CSF (cerebrospinal fluid) and the brain parenchyma. Five leptomeningitis patients and 5 volunteers were enrolled to obtain the pre-enhanced FLAIR images, the early post-enhanced FLAIR images and the delayed post-enhanced FLAIR images, with using a standard dose of contrast, and to measure the signal intensities of the CSF and brain parenchyma. The statistical significances were determined by a mixed procedure and the Wilcoxon rank-sum test (p<0.05). RESULTS: In the rabbits, the signal intensities of the CSF began to increase after an hour of contrast infusion, but those of the parenchyma did not increase. The time of maximum CSF enhancement was 2 hours after contrast infusion (p<0.001; standard estimate=750.43) and we obtained the post-enhanced delayed FLAIR images for clinical studies according to this result. The signal intensities of the CSF in the subarachnoid space were higher in the patient group compared with those of the normal control group on both the early post-enhanced FLAIR images and the delayed post-enhanced FLAIR images (p=0.0096) (p=0.0391). In the patient group, changes of signal intensities of the CSF in the subarachnoid space were more conspicuous on the delayed post-enhanced FLAIR images than on the early post-enhanced FLAIR images (p=0.0042). However, those of the parenchyma were not different in either group. CONCLUSION: The post-enhanced delayed FLAIR images obtained at 2 hours after contrast infusion are more useful for making the the diagnosis of leptomeningitis than are the post-enhanced early FLAIR images.

Histogram Analysis of Noise Performance on Fractional Anisotropy Brain MR Image with Different Diffusion Gradient Numbers

PURPOSE: We wished to analyze, qualitatively and quantitatively, the noise performance of fractional anisotropy brain images along with the different diffusion gradient numbers by using the histogram method. MATERIALS AND METHODS: Diffusion tensor images were acquired using a 3.0 T MR scanner from ten normal volunteers who had no neurological symptoms. The single-shot spin-echo EPI with a Stejskal-Tanner type diffusion gradient scheme was employed for the diffusion tensor measurement. With a b-valuee of 1000 s/mm2, the diffusion tensor images were obtained for 6, 11, 23, 35 and 47 diffusion gradient directions. FA images were generated for each DTI scheme. The histograms were then obtained at selected ROIs for the anatomical structures on the FA image. At the same ROI location, the mean FA value and the standard deviation of the mean FA value were calculated. RESULTS: The quality of the FA image was improved as the number of diffusion gradient directions increased by showing better contrast between the WM and GM. The histogram showed that the variance of FA values was reduced as the number of diffusion gradient directions increased. This histogram analysis was in good agreement with the result obtained using quantitative analysis. CONCLUSION: The image quality of the FA map was significantly improved as the number of diffusion gradient directions increased. The histogram analysis well demonstrated that the improvement in the FA images resulted from the reduction in the variance of the FA values included in the ROI.

Role of EPI in Diagnosing Cavernous Hemangioma & Small HCC: Comparision with Fast T2-Weighted MR Imaging

PURPOSE: To compare single-shot echo-planar MR imaging(EPI) with breath-hold fast T2-weighted imaging(HASTEor Turbo spin-echo T2WI) for evaluation of the role of EPI in distinguishing small hepatocellular carcinoma fromcavernous hemangioma. MATERIALS AND METHODS: We retrospectively evaluated MR images of 35 patients (21 cases ofsmall HCC and 14 cases of cavernous hemangioma). EPI and breath-hold fast T2WI images were obtained and comparedon the basis of lesion detection sensitivity, lesion-to-liver signal intensity ratio(SIR), contrast ratio(CT), andlesion-to-liver contrast to noise ratio(CNR). RESULTS: For the detection of small HCC, the sensitivity of EPI andbreath-hold fast T2WI were equal in 14 of 21 cases(71.4%). The detection sensitivity of cavernous hemangioma withEPI and breath-hold fast T2WI was 100%(14/14). Mean SIR on breath-hold fast T2WI was 2.02+/-0.45 for small HCC and3.65+/-0.97 for cavernous hemangioma; on EPI, the corresponding figures wer 2.91+/-0.57 and 6.98+/-1.37. Mean CR onbreath-hold fast T2WI was 1.16+/-0.58 for small HCC and 2.65+/-0.57 for cavernous hemangioma; On EPI, the figuresobtained were 2.27+/-0.52 and 6.26+/-2.19, respectively. Mean CNR on breath-hold fast T2WI was 14.24+/- 4.098 forsmall HCC and 50.28+/-10.96 for cavernous hemangioma, while on EPI, the corresponding figures were 13.84+/-3.02 and45.44+/-11.21. CONCLUSION: In detecting focal hepatic mass, the sensitivity of EPI and breath-hold fast T2WI arecomparable; for the diagnosis of small HCC and cavernous hemangioma, EPI can provide additional information.

Multishot Echoplanar MR Imaging of the Female Pelvis: Comparison with T2 weighted Fast Spin Echo Imaging

PURPOSE: To compare the usefulness of multishot echoplanar imaging (EPI) with T2-weighted fast spin-echoimaging (FSE) for the evaluation of female pelvic organs and pathologic conditions. MATERIALS AND METHODS:Twenty-nine patients with pelvic lesion underwent MR imaging (GE Medical Systems) using a pelvic array coil (GEMedical Systems). Axial EPI (TR/TE=2,000/80, 6mm slice thickness, 2.5mm gap, multishot 16) and T2-weighted FSE(TR/TE=3,400/117, 5mm slice thickness, 1.5mm gap, ETL=12) were obtained. Overall image quality, the parametrialvenous plexus, anatomy of the uterine zone and outer margin, identification of the ovaries, pelvic pathologiccondition, and frequency of artifact, as seen on EPI and FSE imaging were reviewed separately by two radiologists. RESULTS: For overall imaging quality, EPI was superior to FSE in 14% of patients(4/29), equal in 24%(7/29), andinferior in 62%(18/29). For delineation of the parametrial venous plexus, EPI was superior to FSE in 79%(23/29).For uterine zonal anatomy and the outer margin, EPI was inferior to FSE in 55%(16/29) and in 45%(13/29),respectively. On EPI, visualization of the ovary was rated superior to FSE in 0%(0/9), equal in 52%(15/29), andinferior in 48%(14/29). Conspicuity of pelvic pathologic lesions was superior in 14%(4/29), equal in 52%(15/29),and inferior in 48%(14/29). Image distortion and susceptibility artifacts were seen on EPI in six cases, while onFSE motion artifacts were seen in two cases. CONCLUSIONS: As EPI is inferior to FSE in overall image quality,delineation of the normal anatomy of pelvic organs and conspicuity of pelvic lesions, it cannot replace FSE forimaging the female pelvis. However, because EPI reduces imaging time, further technical progress in this area maystimulate the use of ultrafast imaging of the femal pelvis.

Assessment of Focal Liver Lesions with 4-Phase Dynamic FLASH MR Imaging: Usefulness of Early Image Acquisitionfor Characterization of Arterial Phase

PURPOSE: To document the usefulness of early image acquisition using the contrast-enhanced dynacic MR imagingfor characterization of various focal hepatic lesions during the arterial phase. MATERIALS AND METHODS:Seventy-nine patients with 145 focal liver lesions (71 hemangiomas, 59 hepatocellular carcinomas and 15metastases) underwent breathhold dynamic MR imaging using a fast low-angle shot sequence. After obtainingunenhanced T1-weighted images, four phase MR images were obtained 10, 35, 60 and 300 seconds after starting theinjection. Patterns of contrast enhancement were analyzed for each lesion, with an emphasis on first phase images. RESULTS: Forty-two of the 59 HCCs (71%) showed prominent contrast enhancement during the first phase. HCCssmaller than 2cm in diameter showed a more homogeneous enhancement pattern than those which measured 2cm ormore(24/25 vs 12/17;P<.05). Hemangiomas showed a globular enhancement pattern during the same phase in 51 of 71cases (72%), a finding which was more apparent in those whose diameter was 2cm or more(35/54 vs 16/17, p<.05).During the first phase of imaging, 12 of the 15 metastases showed peripheral enhancement of their thick rim. CONCLUSION: The use of early image acquisition on dynamic MR sequences is helpful in character-izing lesionsaccrding to their pattern of contrast enhancement.

MRCP Using Breath-hold HASTE Sequence: Comparison of Maximum Intensity Projection Image with Single Slice Acquisition Image

PURPOSE: To compare the usefulness of single-slice acquisition imaging and conventional maximum intensity projection imaging, as employed in magnetic resonance cholangiopancreatography (MRCP) using the Half-Fourier Acquisition Single Shot Turbo Spin-Echo(HASTE) sequence. MATERIALS AND METHODS: Five healthy volunteers underwent MRCP using the HASTE sequence on a 1.5T MR unit. Two data acquisition techniques were used : 1) single slice acquisition, with 20 mm slice thickness (imaging time, 2 sec), 2) multi-slice acquisition, with 5 mm slice thickness (imaging time, 19 sec), followed by maximum intensity projection reconstruction. Two radiologists independently evaluated the MRCP images obtained using these two techniques; based on the depiction by each of ten anatomic structures, their quality was graded as excellent (3 points), good (2 points), fair(1 point) or poor(0). Mean scores were totalled, and to compare the quality of the two techniques, these scores were compared. Data was statistically analyzed using the paired student t-test. RESULTS: There was no difference in bile duct image quality between the two techniques. The pancreatic duct was more conspicuous on single-slice (mean score, 1.94) than on maximum intensity projection imaging (mean score, 0.7). The sum of the mean scores of single-slice imaging was 18.75, and that of maximum intensity projection imaging was 14.7 (p=0.42); the general difference between the two techniques was thus statistically insignificant. CONCLUSION: Compared with maximum intensity projection imaging, single-slice imaging had a distinct advantage : acquisition time was short (within 2 sec), thus motion artifacts could be avoided, and there was no need for post-processing. There is a close and direct connection between the avoidance of motion artifact and short acquisition time, but lack of need for post-processing is independent. On single-slice images, the pancreatic duct was more conspicuous than on maximum intensity projection images. The former can therefore be used with patients who experience respiratory difficulty or are suspected to be suffering from disease of the pancreotic duct.