Gregory L Katzman | PubMed Health

PubMed2003

The need for phase-encoding flow compensation in high-resolution intracranial magnetic resonance angiography.

PURPOSE: To demonstrate that the time delay between phase and frequency encoding and the presence of pulsatile blood flow in high-resolution time-of-flight (TOF) imaging of the intracranial arteries (especially near the circle of Willis) can distort the appearance of blood vessels and result in a cross-hatch-appearing artifact in surrounding tissue. MATERIALS AND METHODS: Two techniques to reduce the artifact, tri-directional flow compensation (3DFC) and elliptical-centric (EC) phase-encoding order, are investigated in five volunteer studies. RESULTS: 3DFC eliminates the pulsation-related artifacts and the vessel distortion. A residual amplitude variation artifact is observed. EC phase encoding nearly eliminates the pulsatile motion-related artifact, but it does not eliminate vessel distortion. CONCLUSION: The combination of 3DFC and EC phase encoding appears to provide the greatest artifact reduction in the five volunteer studies performed.

Adult↗

PubMed2002

Improved efficiency in double-inversion fast spin-echo imaging.

Double-inversion fast spin-echo (FSE) pulse sequences can be designed to provide excellent suppression of blood signal in black-blood MRI. However, because a nonselective inversion is used, these sequences typically have been highly inefficient. In this work it is demonstrated that the efficiency of double-inversion sequences can be greatly improved by a form of interleaving in which all of the slices to be imaged in a single pass are reinverted each time a signal is obtained from any single slice. To date, several studies have demonstrated a high level of blood suppression with these more efficient techniques.

Aged↗

PubMed2002

Magnetoencephalographically directed review of high-spatial-resolution surface-coil MR images improves lesion detection in patients with extratemporal epilepsy.

PURPOSE: To determine whether (a) interictal magnetoencephalographic (MEG) epileptiform activity corresponds to anatomic abnormalities at magnetic resonance (MR) imaging, (b) high-spatial-resolution MR imaging depicts lesions in regions without MEG spike activity, (c) MEG-directed review of high-spatial-resolution MR images enables detection of abnormalities not apparent on conventional MR images, and (d) MEG information results in a greater number of diagnosed lesions at re-review of conventional MR images. MATERIALS AND METHODS: Twenty patients with neocortical epilepsy were evaluated with MEG, conventional brain MR imaging with a head coil, and high-spatial-resolution MR imaging with either a surface coil (n = 17) or a high-spatial-resolution birdcage coil (n = 3). Abnormal MEG foci were compared with corresponding anatomic areas on conventional and high-spatial-resolution MR images to determine the presence (concordance) or absence (discordance) of anatomic lesions corresponding to foci of abnormal MEG activity. RESULTS: Forty-four epileptiform MEG foci were identified. Twelve foci (27%) were concordant with an anatomic abnormality at high-spatial-resolution MR imaging, and 32 foci (73%) were discordant. Results of high-spatial-resolution MR imaging were normal in eight patients, and 23 lesions were detected in the remaining 12 patients. Twelve lesions (52%) were concordant with abnormal MEG epileptiform activity, and 11 (48%) were discordant (ie, there was normal MEG activity in the region of the anatomic abnormality). At retrospective reevaluation of conventional MR images with MEG guidance, four occult gray matter migration lesions that had initially been missed were observed. An additional patient with MEG-concordant postoperative gliosis was readily identified with high-spatial-resolution MR images but not with conventional MR images. CONCLUSION: Review of MEG-localized epileptiform areas on high-spatial-resolution MR images enables detection of epileptogenic neocortical lesions, some of which are occult on conventional MR images.

Adult↗