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Michael H Lev

Publications and source records attributed to Michael H Lev.

At least 37 records · Page 2Linked to original sources
PubMed2004

The effect of varying user-selected input parameters on quantitative values in CT perfusion maps.

RATIONALE AND OBJECTIVES: Deconvolution-based software can be used to calculate quantitative maps of cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT) from first-pass computed tomography perfusion (CTP) datasets. The application of this software requires the user to select multiple input variables. The purpose of this study was to investigate the degree to which both major and minor variations of these user-defined inputs would affect the final quantitative values of CBF, CBV, and MTT. MATERIALS AND METHODS: A neuroradiologist constructed CBF, CBV, and MTT maps using standard methodology with commercially available software (GE Functool Version 1.9s) from CTP datasets of three acute stroke patients. Each map was reconstructed multiple times by systematically and independently varying the following parameters: postenhancement and preenhancement cutoff values, arterial and venous region-of-interest (ROI) placement, and arterial and venous ROI size. The resulting quantitative CTP values were compared using identical ROIs placed at the infarct core. RESULTS: Major variations of either arterial ROI placement or arterial and venous ROI size had no significant effect on the mean CBF, CBV, and MTT values at the infarct core (p > .05). Even minor variations, however, in the choice of venous ROI placement or in pre- and postenhancement cutoff values significantly altered the quantitative values for each of the CTP maps, by as much as threefold. CONCLUSION: Even minor variations of user-defined inputs can significantly influence the quantitative, deconvolution-based CTP map values of acute stroke patients. Although quantitation was robust to the choice of arterial ROI placement and arterial or venous ROI size, it was strongly dependent on the choice of venous ROI location and pre- and postenhancement cut-off values. Awareness of these results by clinicians may be important in the creation of quantitatively accurate CTP maps.

Adult↗
PubMed2004

Dynamic magnetic resonance perfusion imaging of brain tumors.

In this paper, we review the technique of contrast-enhanced magnetic resonance (MR) perfusion imaging of brain neoplasms, with an emphasis on its clinical applications and utility. We start with a discussion of MR perfusion techniques available today and their relative merits and shortcomings. Next, the ability of MR perfusion to provide a preoperative assessment of tumor histology is examined. We also discuss the role of MR perfusion in helping guide tumor biopsy, and its advantages over more conventional methods. We will scrutinize the use of MR perfusion for assessing true lesion extent, in contrast to conventional MR imaging and other MR techniques. We will discuss the role of MR perfusion in differentiating treatment effects, such as radiation necrosis, from tumor recurrence. Finally, the future potential applications of this technology in the setting of novel antiangiogenic therapies for brain tumors will be addressed.

Biopsy↗
PubMed2004

Glial tumor grading and outcome prediction using dynamic spin-echo MR susceptibility mapping compared with conventional contrast-enhanced MR: confounding effect of elevated rCBV of oligodendrogliomas [corrected].

BACKGROUND AND PURPOSE: The MR imaging characteristics of oligodendrogliomas and astrocytomas on spin-echo (SE), echo-planar relative cerebral blood volume (rCBV) maps, to our knowledge, have not previously been emphasized. We compared the specificity of SE rCBV mapping with that of conventional, contrast material-enhanced MR imaging in differentiating high- from low-grade glial tumors and in predicting survival of patients with these lesions. METHODS: Thirty consecutive adult patients with suspected gliomas underwent conventional and rCBV MR imaging. Representative maximal rCBV regions of interest were chosen from each lesion. Resultant values were normalized to those of corresponding, contralateral, uninvolved regions. These normalized CBV (nCBV) values were correlated with degree of contrast enhancement, histopathologic tumor grade, and survival. RESULTS: Twenty-two patients had astroctyomas and eight had oligodendrogliomas. With an nCBV cutoff ratio of 1.5, 13 of 13 high-grade astrocytomas were correctly categorized, three of which did not enhance. Seven of nine low-grade astrocytomas were correctly classified by their nCBV values, including one enhancing lesion. Of eight oligodendrogliomas, four of four high-grade and two of four low-grade tumors had elevated nCBV values; two low-grade oligodendrogliomas enhanced, one with nCBV greater than 1.5 and one with nCBV less than 1.5. In 19 patients with astrocytoma for whom survival data were available, correlation with survival was better for nCBV (mean survival 91 +/- 14 months for nCBV < 1.5 versus 24 +/- 27 months for nCBV > 1.5, P <.0001) than for enhancement (mean survival 61 +/- 35 months without enhancement versus 22 +/- 29 months with enhancement, P =.03). CONCLUSION: Elevated SE rCBV was a sensitive, but not specific, marker for high-grade histopathology: all high-grade tumors had nCBV foci values greater than 1.5. No tumor with nCBV region of interest less than 1.5 was high grade (100% predictive value for excluding high grade). Degree of nCBV elevation was a stronger predictor of both tumor grade and survival than was degree of enhancement. A significant proportion of low-grade glial neoplasms, most notably oligodendrogliomas, may display high rCBV foci not reflective of high-grade histopathology.

Adolescent↗
PubMed2004

Comparison of image quality between conventional and low-dose nonenhanced head CT.

BACKGROUND AND PURPOSE: Increasing use of CT for evaluating neurologic disease may expose patients to considerable levels of ionizing radiation. We compared the image quality of low-mAs head CT scans with that of conventional nonenhanced scans. METHODS: Conventional head CT scans were obtained in 20 patients (all >65 years with history of non-CNS malignancy) by using a multidetector technique: 170 mA and 1-second scanning time (ie, 170 mAs), 140 kVp, table speed of 7.5 mm per rotation, pitch of 0.75, section thickness of 5 mm, and field of view of 25 mm. A limited volume helical data acquisition covering four 5-mm-thick images was obtained by using 90 mAs but otherwise the same parameters. Three neuroradiologists visually rated the resulting images for quality in a blinded comparison. Representative 1- to 4-mm(2) regions of interest were chosen in gray matter and white matter locations. Conspicuity and the contrast-to-noise ratio were analyzed. Statistical comparisons were done by using the Student t test. RESULTS: Mean gray matter conspicuity was not significantly different between the 170- and 90-mAs groups (0.39 +/- 0.19 vs 0.41 +/- 0.03, P =.32). Mean gray matter contrast-to-noise ratio was approximately 22% higher with 170 mAs than with 90 mAs (1.77 +/- 0.52 vs 1.39 +/- 0.38, P =.005). All 90-mAs images were rated as having slightly greater image noise than the 170-mAs scans but with sufficient perceived resolution. CONCLUSION: Although 90-mAs head CT images were moderately noisier than 170-mAs images, they were rated as having acceptable diagnostic quality.

Aged↗
PubMed2003

Spontaneous recanalization of internal carotid artery occlusion.

BACKGROUND AND PURPOSE: Spontaneous recanalization of an acutely occluded internal carotid artery (ICA) is an important phenomenon, the natural history and incidence of which have been incompletely studied. Although conventional catheter arteriography remains the gold standard for distinguishing total arterial occlusion from hairline residual lumen, CT angiography (CTA) is able to make this distinction noninvasively and more sensitively than either unenhanced MR angiography or ultrasound. The purpose of this report is to raise awareness of spontaneous recanalization and to demonstrate the possible use of CTA in following up cases of ICA occlusion. METHODS: We describe here 2 cases of acute cervical ICA occlusion seen on CTAs done at our institution. RESULTS: Follow-up CTAs in both cases showed spontaneous recanalization of the ICA requiring ipsilateral carotid endarterectomy within 1 month of the initial presentation. CONCLUSIONS: CTA, an accurate, rapid, and less invasive modality than conventional catheter arteriography, can be used to serially monitor anticoagulated patients with new-onset ICA occlusion for potential spontaneous vascular recanalization. The ability to conveniently assess ICA patency not only may influence management of individual patients but also could help us better establish the true incidence of spontaneous carotid recanalization in future studies.

Aged↗
PubMed2003

Coregistration of head CT comparison studies: assessment of clinical utility.

RATIONALE AND OBJECTIVES: The authors evaluated the clinical utility of image coregistration in the interpretation of follow-up computed tomographic (CT) studies of the head. MATERIALS AND METHODS: Fourteen patients with 34 intracranial lesions underwent follow-up head CT. The images were coregistered automatically with proprietary software on a standard personal computer, and all patient demographic data were removed. A neuroradiologist read the coregistered images several days after first reading the nonregistered images. The reading was repeated some months later to assess intraobserver variability, and a second reader was recruited so that interobserver variability also could be assessed. The interpretations of nonregistered images served as controls for the interpretations of coregistered images. Readers were asked to assess changes in lesion size quantitatively and to record the time it took to evaluate each case. Differences in interpretation speed were evaluated with the t test. Univariate analysis was used to measure accuracy; interpretations were compared with those of a nonblinded senior neuroradiologist, which served as the diagnostic standard. Intra- and interindividual variability were assessed with the kappa statistic. RESULTS: The time needed to read the studies decreased by an average of 65.6% (P < .05), with statistically significant reductions for each reader. Coregistration also changed the interpretation results in 21.9% of cases. Coregistration increased the accuracy of reading, but not significantly. Intraobserver variability improved from 0.3554 to 0.7328 with coregistration, and interobserver variability improved from 0.2670 to 0.3309. CONCLUSION: Image coregistration is technically feasible and accurate. Coregistration of follow-up studies significantly reduces the time needed for comparison and interpretation. It does not detract from the accuracy of interpretation of follow-up studies and tends to decrease intra- and interobserver variability.

Brain Diseases↗
PubMed2003

Correlation of early dynamic CT perfusion imaging with whole-brain MR diffusion and perfusion imaging in acute hemispheric stroke.

BACKGROUND AND PURPOSE: Compared with MR imaging, dynamic CT perfusion imaging covers only a fraction of the whole brain. An important assumption is that CT perfusion abnormalities correlate with total ischemic volume. The purpose of our study was to measure the degree of correlation between abnormalities seen on CT perfusion scans and the volumes of abnormality seen on MR diffusion and perfusion images in patients with acute large-vessel stroke. METHODS: Fourteen patients with acute hemispheric stroke symptoms less than 12 hours in duration were studied with single-slice CT perfusion imaging and multislice MR diffusion and perfusion imaging. CT and MR perfusion studies were completed within 2.5 hours of one another (mean, 77 minutes) and were reviewed independently by two neuroradiologists. Hemodynamic parameters included cerebral blood flow (CBF), cerebral blood volume (CBV), and mean transit time (MTT). Extents of abnormality on images were compared by using Kendall correlation. RESULTS: Statistically significant correlation was found between CT-CBF and MR-CBF abnormalities (tau = 0.60, P =.003) and CT-MTT and MR-MTT abnormalities (tau = 0.65, P =.001). Correlation of CT-CBV with MR-CBV approached significance (tau = 0.39, P =.06). Extent of initial hyperintensity on diffusion-weighted images correlated best with extent of MR-CBV abnormality (tau = 0.69, P =.001), extent of MR-MTT abnormality (tau = 0.67, P =.002), and extent of CT-CBV abnormality (tau = 0.47, P =.02). CONCLUSION: Good correlation was seen between CT and MR for CBF and MTT abnormalities. It remains uncertain whether CT perfusion CBV abnormalities correspond well to whole-brain abnormalities.

Acute Disease↗
PubMed2002

Noncontrast conventional computed tomography in the evaluation of acute stroke.

The advantages of CT scanning in the assessment of hyperacute stroke patients include convenience, accuracy, speed, and low cost. CT scanning is presently considered to be the standard of care for the detection of acute extra-axial and parenchymal hemorrhage, although newer MRI techniques are challenging this claim. The accuracy of CT scanning for stroke detection can be optimized by the use of appropriate scanning technique, as well as interactive image review at a picture archiving and communication system workstation using narrow window and level settings. More importantly, CT scanning has prognostic value for patients receiving thrombolytic treatment by helping to predict both responses to treatment and hemorrhage risk. Finally, as will be discussed in other articles in this issue, CT angiography can be performed in the same imaging session as noncontrast CT scanning without substantially increasing the time required for patient evaluation. This provides data regarding vascular patency and tissue perfusion, which are valuable in the triage of stroke patients.

Brain↗
PubMed2002

CT perfusion scanning with deconvolution analysis: pilot study in patients with acute middle cerebral artery stroke.

PURPOSE: To measure mean cerebral blood flow (CBF) in ischemic and nonischemic territories and in low-attenuation regions in patients with acute stroke by using deconvolution-derived hemodynamic imaging. MATERIALS AND METHODS: Twelve patients with acute middle cerebral artery stroke and 12 control patients were examined by using single-section computed tomography (CT) perfusion scanning. Analysis was performed with a deconvolution-based algorithm. Comparisons of mean CBF, cerebral blood volume (CBV), and mean transit time (MTT) were determined between hemispheres in all patients and between low- and normal-attenuation regions in patients with acute stroke. Two independent readers examined the images for extent of visually apparent regional perfusion abnormalities. The data were compared with extent of final infarct in seven patients with acute stroke who underwent follow-up CT or magnetic resonance imaging. RESULTS: Significant decreases in CBF (-50%, P =.001) were found in the affected hemispheres of patients with acute stroke. Significant changes in CBV (-26%, P =.03) and MTT (+111%, P =.004) were also seen. Significant alterations in perfusion were also seen in low- compared with normal-attenuation areas. Pearson correlation between readers for extent of CBF abnormality was 0.94 (P =.001). Intraobserver variation was 8.9% for CBF abnormalities. CONCLUSION: Deconvolution analysis of CT perfusion data is a promising method for evaluation of cerebral hemodynamics in patients with acute stroke.

Adult↗
PubMed2002

CT angiography with whole brain perfused blood volume imaging: added clinical value in the assessment of acute stroke.

BACKGROUND AND PURPOSE: In CT angiographic and perfusion imaging (CTA/CTP), rapid CT scanning is performed during the brief steady state administration of a contrast bolus, creating both vascular phase images of the major intracranial vessels and perfused blood volume-weighted parenchymal phase images of the entire brain. We assessed the added clinical value of the data provided by CTA/CTP over that of clinical examination and noncontrast CT (NCCT) alone. METHODS: NCCT and CTA/CTP imaging was performed in 40 patients presenting with an acute stroke. Short clinical vignettes were retrospectively prepared. After concurrent review of the vignettes and NCCT, a stroke neurologist rated infarct location, vascular territory, vessel(s) occluded, and Trial of Org 10172 in Acute Stroke Treatment (TOAST) and Oxfordshire Community Stroke Project classifications. The ratings were repeated after serial review of each of the CTA/CTP components: (1) axial CTA source images; (2) CTP whole brain blood volume-weighted source images; and (3) maximum-intensity projection 3-dimensional reformatted images. The sequential ratings for each case were compared with the final discharge assessment. RESULTS: Compared with the initial review after NCCT, CTA/CTP improved the overall accuracy of infarct localization (P<0.001), vascular territory determination (P=0.003), vessel occlusion identification (P<0.001), TOAST classification (P=0.039), and Oxfordshire Community Stroke Project classification (P<0.001) by 40%, 28%, 38%, 18%, and 32%, respectively. CONCLUSIONS: Admission CTA/CTP imaging significantly improves accuracy, over that of initial clinical assessment and NCCT imaging alone, in the determination of infarct localization, site of vascular occlusion, and Oxfordshire classification in acute stroke patients.

Aged↗
PubMed2002

Influence of availability of clinical history on detection of early stroke using unenhanced CT and diffusion-weighted MR imaging.

OBJECTIVE: The radiologic diagnosis of stroke requires accurate detection and appropriate interpretation of relevant imaging findings; both detection and interpretation may be influenced by knowledge of the patient's presentation. In our study, we evaluated the effect of the availability of clinical history on the sensitivity for stroke detection using unenhanced CT and diffusion-weighted MR imaging. MATERIALS AND METHODS: The records of 733 consecutive patients with a clinically based admission diagnosis of early stroke were reviewed. Among the criteria for inclusion in our study were the availability of an unenhanced CT scan (561 cases) or diffusion-weighted MR imaging examination (409 cases) obtained at admission and a discharge diagnosis indicating whether a patient had actually had a stroke. The radiology requisition forms, available at the time of image interpretation, were classified as either indicating or not indicating a clinical suspicion of early stroke. Sensitivity, specificity, and accuracy of stroke detection were computed, stratified by the presence or absence of an available history indicating suspicion of stroke. Results were compared using the Fisher's exact two-tailed test. RESULTS: Unenhanced CT sensitivity was 52% (specificity, 95%) for the suspicion-of-stroke group and 38% (specificity, 89%) for the no-suspicion-of-stroke group (p = 0.008). Diffusion-weighted MR imaging sensitivity was 95% (specificity, 94%) for the suspicion-of-stroke group and 94% (specificity, 98%) for the no-suspicion-of-stroke group (p = 0.822). CONCLUSION: Availability of a clinical history indicating that early stroke is suspected significantly improves the sensitivity for detecting strokes on unenhanced CT without reducing specificity. In contradistinction, the availability of such a history did not significantly improve the sensitivity for detecting stroke using diffusion-weighted MR imaging. Whenever possible, relevant clinical history should be made available to physicians interpreting emergency CT scans of the head.

Aged↗
PubMedDate not supplied

US of neurovascular occlusive disease: interpretive pearls and pitfalls.

Ultrasonography (US) of the head and neck is a convenient but operator-dependent screening tool for detection and diagnosis of neurovascular occlusive disease. In US examination of the extracranial carotid arteries, stenosis is most commonly graded according to the peak systolic Doppler velocity in the region of maximal luminal narrowing rather than according to the percentage of atheromatous plaque occupying the lumen. However, the peak systolic velocity is not always reliable in estimation of the degree of stenosis. General diagnostic pitfalls include technical difficulties with scanning, failure to review the spectral waveform patterns, the presence of additional stenotic lesions, and anatomic variants. Specific examples of pitfalls include tandem lesions, differentiation of pseudo-occlusion from true total occlusion, pseudonormalization of velocities in cases of very severe stenosis, lesions of the carotid artery origin or aortic valve, progression of subclavian steal, underestimation of severe stenosis due to heavily calcified plaque, a persistent trigeminal artery, and contralateral carotid artery stenosis. Although conventional angiography remains the standard of reference for assessment of carotid artery disease, recognition of these common sources of error in US can improve the accuracy of this noninvasive test in diagnosis of carotid artery occlusion.

Arterial Occlusive Diseases↗