New Techniques in MRI and their Clinical Applicability

2007-8 secures the era of higher field MR imaging and ushers in the era of superfast and motion-free MR imaging. As well, several newer neuroimaging techniques have migrated from the MR research laboratories to clinical practice. Among them, the derivatives of diffusion weighted imaging, especially diffusion tractography (fibertrack imaging) and diffusion-weighted whole-body imaging (DWIBS), bolus track and arterial spin labeling perfusion MR imaging, time resolved MR angiography (4D TRAK, TWIST, and 4D TRICKS), susceptibilityweighted imaging and motion correction imaging (propeller, blade, multivane).curriculum_fellow; GVSdiffusionweightedimaging; GVScomputedtomography; GVSmagneticresonanceimaging; GVSgeneralimaging; EXAMmr

The Future of Neuroimaging

The state of clinical neuroimaging in 2007-08 begins with the migration from conventional CT scanners to 64 multichannel CT which now represents the standard of care. Where CT scanning formerly meant slice by slice acquisition of data, volumetric acquisitions of body parts and regions is now the norm. Moreover, while CT images are most typically presented and interpreted in the axial plane, it is now expected that sagittal and coronal images are presented in the spine, as are coronal images of the face, orbit, and temporal bone, as are coronal images of the chest, abdomen and pelvis.curriculum_fellow; GVScomputedtomography; GVSmagneticresonanceimaging; GVSgeneralimagin

Multi-slice CT angiography of small cerebral aneurysms: is the direction of aneurysm important in diagnosis?

Multi-slice CT (MSCT) has great potential in evaluation of vascular structures. Our purpose was to investigate if there is any difference in detection of superiorly, inferiorly and horizontally directed small cerebral aneurysms (<5 mm) on MSCTA compared to digital subtraction angiography (DSA) or surgery. One hundred and three consecutive patients who underwent MSCTA and DSA or surgery were included in the study. MSCTA and DSA results were evaluated independently by two different neuroradiologists who performed aneurysm detection, quantitation, and characterization using 2D multiplanar reconstructions, 3D maximum intensity projection and volume-rendered techniques. MSCTA detected 49 small cerebral aneurysms (<5 mm) in 37 (36%) of 103 patients. The overall sensitivity, specificity, and accuracy of MSCTA for detecting small aneurysms were 0.85, 0.65, and 0.79, respectively. There was moderate agreement between MSCTA and DSA/surgery for detecting small aneurysms ( κ: 0.51). The sensitivity of detecting small aneurysms directed superiorly, inferiorly and horizontally was 0.94, 0.84, and 0.75, respectively. There was no statistically significant difference in detection between small aneurysms directed superiorly, inferiorly and horizontally on MSCTA ( P > 0.05). The direction of small cerebral aneurysms is not important in diagnosis on multi-slice CT scanners, although the detection of small cerebral aneurysms with superior or inferior direction is slightly easier than the detection of horizontally directed aneurysms

Central-variant posterior reversible encephalopathy syndrome: brainstem or basal ganglia involvement lacking cortical or subcortical cerebral edema

Although posterior reversible encephalopathy syndrome (PRES) typically involves cortical or subcortical edema of the cerebrum, only individual cases have been described of a variant involving the central brainstem and basal ganglia and lacking cortical and subcortical edema. We evaluated FLAIR and T2-weighted images of 124 patients with confirmed PRES to determine the incidence of this uncommon variant, which we refer to as the "central variant"; to determine which structures are involved in this variant; and to determine the associated causes. We found that five of the 124 patients (4%) with PRES had MR findings consistent with the central variant-that is, either brainstem or basal ganglia involvement and a lack of cortical or subcortical edema of the cerebrum. The thalami were involved in all five PRES patients with MR findings consistent with the central variant, but there was variable involvement of the posterior limb of the internal capsule (4/5), cerebellum (3/5), and periventricular white matter (3/5); in each patient, there was improvement both clinically and on MRI. The causes of PRES in these five patients were hypertension (n=2), cyclosporine (n=2), and eclampsia (n=1). The incidence of the central variant may be increasing because of an improving awareness of the diverse imaging patterns of PRES

Anatomy and Frequency of Large Pontomesencephalic Veins on 3D CT Angiograms of the Circle of Willis

BACKGROUND AND PURPOSE: The pontomesencephalic veins (PMVs), especially the anterior PMV, are sometimes large enough that they could potentially affect the interpretation of CT angiograms of the circle of Willis. We investigated the frequency and anatomy of visible PMVs on 3D CT angiograms. METHODS: CT angiograms of 211 consecutive patients who underwent CT angiography for a variety of clinical indications were evaluated retrospectively. Images evaluated by consensus between two neuroradiologists were maximum intensity projection and volume-rendered 3D CT angaiograms. RESULTS: Visible PMVs were present on 3D CT angiograms in 11 (5.2%) of 211 patients. Eight of 11 patients had a visible anterior PMV behind the basilar artery. In four patients, the venous caliber of the anterior PMV was sufficiently large enough to be potentially confused with arterial structures. In one patient, 3D CT angiography revealed a large anterior PMV (∼2.6 mm in diameter) in the interpeduncular cistern, which had been mistaken for subarachnoid hemorrhage on a nonenhanced CT scan. Two patients had interpeduncular veins of the anterior PMV draping over the dome of a basilar tip aneurysm. In only one patient was the anterior PMV visible possibly owing to arteriovenous malformation. One patient had visible lateral mesencephalic veins, and four patients had visible transverse pontine veins. In one case, on certain views, the transverse pontine veins appeared to arise from the basilar artery. CONCLUSION: Because of their small size, PMVs were seen only infrequently on 3D CT angiograms, but neuroradiologists should be familiar with the normal variants of large PMVs to avoid diagnostic and anatomic confusion

Reperfusion Phenomenon Masking Acute and Subacute Infarcts at Dynamic Perfusion CT: Confirmation by Fusion of CT and Diffusion-Weighted MR Images

OBJECTIVE. The purpose of this study was to evaluate cerebral blood flow, cerebral blood volume, mean transit time, time to peak, and delay in a selected sample of patients with visually normal or increased cerebral blood volume to facilitate detection of a postischemic CT perfusion hyperperfusion-reperfusion phenomenon that may mask subacute and acute infarcts. MATERIALS AND METHODS. Ten patients were included who had visually normal or elevated cerebral blood volume in infarcts larger than 1.5 cm confirmed on diffusion-weighted MR images within 48 hours of perfusion CT. The cases were selected from 371 perfusion CT studies of stroke patients (99 associated with positive diffusion-weighted imaging findings) reviewed over 2.5 years on a 64-MDCT scanner. The perfusion CT images were fused to the diffusion-weighted images for measurement of cerebral blood volume, cerebral blood flow, mean transit time, time to peak, and delay in each infarct versus the contralateral hemisphere. Two neuroradiologists reviewed the images in consensus. RESULTS. The mean time between symptom onset and perfusion CT was 3.9 days. Infarcts were in the middle cerebral artery (n = 7) and posterior cerebral artery (n = 3) distributions. Significant differences versus the contralateral finding were found in cerebral blood volume (p = 0.016; mean increase, 30.0%), mean transit time (p = 0.007; mean increase, 38.1%), time to peak (p = 0.005; mean increase, 17.7%), and delay (p = 0.030; mean increase, 124.9%). The difference in cerebral blood flow (p = 0.785; mean increase, 1.8%) was not statistically significant. Infarcts became enhanced on the dynamic perfusion CT images of eight of 10 patients and on the contrast-enhanced T1-weighted MR images of six of nine patients. CONCLUSION. Visual inspection of cerebral blood volume and cerebral blood flow maps alone is insufficient in the evaluation of infarcts. Mean transit time, time to peak, and delay maps also should be reviewed with dynamic source images to prevent misinterpretation of findings as false-negative. This phenomenon is unlikely to occur hyperacutely (< 8 hours after onset)