Atsushi Nozaki

Diffusion-weighted echo planar imaging of ovarian tumors: is it useful to measure apparent diffusion coefficients?

Purpose Our goal was to test the hypothesis, as previously reported in other studies, that apparent diffusion coefficients (ADCs) provide specific information to diagnose ovarian tumors, especially to discriminate between benign and malignant lesions. Method T1-and T2-weighted spin echo imaging and diffusion-weighted echo planar imaging were performed in 31 women with 61 cystic components of ovarian tumors. Results The lesions that showed typical watery intensity, hypointensity in T1-weighted imaging, and hyperintensity in T2-weighted imaging had similar ADCs, ranging from 1.54 to 1.84 × 10−3 mm2 /s. The lesions that showed signal intensity different from typical watery intensity in conventional MRI tended to have low ADCs. In endometrial cysts, the mean ADC of the subgroup that showed typical watery intensity was higher than that of other subgroups. Conclusion With conventional MRI, a tendency of ADCs could be predicted. ADCs may not provide additional information, especially to discriminate benign from malignant lesions.

Fat-suppressed T2-weighted MRI of the liver: Comparison of respiratory-triggered fast spin-echo, breath-hold single-shot fast spin-echo, and breath-hold fast-recovery fast spin-echo sequences

The purpose of our study was to compare the value of respiratory‐triggered fast spin‐echo, breath‐hold single‐shot fast spin‐echo, and breath‐hold fast‐recovery fast spin‐echo sequences in detecting hepatic lesions. Fat‐suppressed T2‐weighted magnetic resonance (MR) images obtained with the three sequences in 36 patients with 138 lesions and nine patients without lesions were prospectively analyzed. Quantitative and qualitative analyses, including receiver operating characteristic (ROC) analyses, were performed. The mean lesion‐to‐liver contrast‐to‐noise ratio (CNR) for hepatic lesions was highest with the respiratory‐triggered fast spin‐echo sequence. On the basis of receiver‐operating characteristic analyses, tumor detection rates were higher with the breath‐hold fast‐recovery fast spin‐echo sequence (Az = 0.94) than with the respiratory‐triggered fast spin‐echo sequence (AZ = 0.80, P < 0.0001) or the single‐shot fast spin‐echo sequence (Az = 0.77, P < 0.0001). The image quality with the breath‐hold fast‐recovery fast spin‐echo sequence was acceptable in all patients. The breath‐hold fast‐recovery fast spin‐echo sequence provided the highest tumor detection in a short imaging time, although the mean lesion‐to‐liver CNRs were inferior to those of the respiratory‐triggered fast spin‐echo and the breath‐hold single‐shot fast spin‐echo sequences. J. Magn. Reson. Imaging 2001;14:439–449.

MRA of intracranial aneurysm models: a comparison of contrast-enhanced three-dimensional MRA with time-of-flight MRA.

PURPOSE The purpose of our study was to compare contrast-enhanced 3D MR angiography (MRA) using ultrafast spoiled gradient-recalled acquisition in the steady state (SPGR) with 2D and 3D time-of-flight (TOF) MRA for visualization of intracranial lateral saccular aneurysm models. METHOD We used lateral saccular aneurysm models with a height of 10 mm and neck sizes of 2.5 and 10 mm. Imaging was performed using a 1.5 T MR system with a head coil. Contrast-enhanced 3D MR angiograms were obtained using 3D ultrafast SPGR sequence with and without the MR Smartprep technique. Two-dimensional and 3D TOF MR angiograms were also obtained. RESULTS Contrast-enhanced multiphase 3D MR angiograms taken every 5 s after injection of contrast medium proved superior to the other MRA techniques for delineating lateral saccular aneurysm models. Contrast-enhanced 3D MRA images taken with inadequate delay after MR Smartprep trigger showed poor visualization of the aneurysm model. CONCLUSION Use of contrast-enhanced multiphase 3D MRA with ultrafast SPGR with shorter TR and TE resulted in clear images of the lateral saccular aneurysm model.

Double hepatic arterial phase MRI of the liver with switching of reversed centric and centric K-space reordering.

OBJECTIVE The purpose of our study was to evaluate the clinical feasibility and usefulness of a 2D spoiled gradient-recalled echo MR sequence with serial switching of reversed centric and centric k-space reordering for high-spatial-resolution gadolinium-enhanced double hepatic arterial phase (HAP) MRI of the liver. SUBJECTS AND METHODS MR images (frequency, 512; phase encoding without interpolation, 224; 6-mm thickness with 1-mm gap; 30 slices per 18 seconds) were obtained with multiphase imaging in which central k-space line data were filled 10, 21, 49, and 181 seconds after arrival of contrast medium in the abdominal aorta for the early HAP (reversed centric reordering, center of k-space lines acquired at end of acquisition), late HAP (centric reordering, center of k-space lines at beginning of acquisition), portal venous phase (centric reordering), and equilibrium phase (centric reordering), respectively, in 102 consecutive patients with suspected liver disease, including 48 untreated hepatocellular carcinomas (HCCs) in 35 patients. Images were quantitatively assessed for degree of contrast enhancement in the abdominal aorta, spleen, portal trunk, liver parenchyma, hepatic veins, and HCCs. Images were qualitatively assessed for the effectiveness of contrast enhancement in each phase and for degree of image degradation due to artifacts. RESULTS Enhancement of the abdominal aorta peaked in the early HAP, of the portal trunk in the late HAP, and of the hepatic parenchyma and veins in the portal venous phase. Mean HCC-to-liver contrast peaked in the early HAP and turned to a negative value in the portal venous and equilibrium phases. Sufficient image quality was achieved in 99 (97%) of the patients. One of the other three patients had motion artifacts due to body motion, and the other two had unsatisfactory respiratory suspension. Scan timing for early and late HAP was optimal in 74 (73%) of the patients, for late HAP lagged in 20 (20%), for early HAP was premature in six (6%), and for early HAP lagged in five (5%) of the patients. CONCLUSION We confirmed the feasibility and usefulness of a 2D gadolinium-enhanced double HAP spoiled gradient-recalled echo sequence incorporating serial switching of reversed centric and centric k-space reordering. This method has the potential for use in high-spatial-resolution double HAP MRI for the diagnosis of hypervascular HCC.

Magnetic resonance portography using contrast-enhanced fat-saturated three-dimensional steady-state free precession imaging.

To assess the feasibility of contrast‐enhanced fat‐saturated three‐dimensional steady‐state free precession (FIESTA) imaging for contrast‐enhanced magnetic resonance (MR) portography.

MR angiography of the renal artery: comparison of breath-hold two-dimensional phase-contrast cine technique with the phased-array coil and breath-hold two-dimensional time-of-flight technique with the body coil

Breath-hold 2D phase-contrast (PC) cine MR angiography with a phased-array coil and 2D time-of-flight (TOF) MR angiography were performed in the renal arteries and their findings were compared. Breath-hold 2D thin slice PC and TOF MR angiography were performed in 10 normal volunteers for renal arteries. A PC technique with k-space segmentation was utilized with the phased-array coil. A PC technique provided visualization of the renal artery more distally than a TOF technique (4.8 +/- 0.5 cm vs. 3.7 +/- 0.8 cm). With cardiac triggering, distal renal arteries were well demonstrated in PC MR angiography. On PC images, up- or downward movements of the mid to distal renal arteries with aortic pulsatility were recognized. The quality of the images was better with the PC than with the TOF technique (3.4 vs. 2.7). The mid to distal portions of the renal arteries translationally move with aortic pulsatility. To consistently visualize and evaluate them on MR angiography, cardiac triggering might be required to reduce the effects of pulsatile motions of the renal artery in the use of a phased-array coil.