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Richard Frayne

Publications and source records attributed to Richard Frayne.

28 records · Page 2Linked to original sources
PubMed2003

Contrast-enhanced MR angiography of the intracranial circulation.

NCE MRA can provide the authors with useful diagnostic information in patients suffering from intracranial vascular disease, often leading to improved or altered treatment decisions. Most centers have used 3D TOF for evaluation of stroke-the most common cerebral vascular disease. Because of slow and disturbed flow, conventional 3D TOF MRA tends to overestimate stenotic lesions and occluded arteries and this can confound neurovascular assessment in stroke patients. Post contrast 3D TOF techniques provide a more robust and more specific method for imaging the intracranial circulation that overcomes the drawbacks of conventional 3D TOF. In the setting of acute ischemic stroke, the authors have found that the combination of conventional and CE 3D TOF MRA improves their overall diagnostic ability. Dynamic and time-resolved CE MRA techniques have evolved rapidly. Time-resolved CE MRA, in particular, is emerging as a useful technique for imaging dynamic vascular pathologies such as AVMs. Unfortunately, time-resolved MRA of the intracranial circulation provides images with low spatial resolution and is currently limited to subsecond frame rate 2D acquisitions, and less than 2 seconds frame rates for 3D acquisitions. Nevertheless, like in other vascular regions, CE MRA represents a milestone for non-invasive intracranial vascular imaging. The continuing development of CE MRA techniques and of new contrast agents will lessen the need for intra-arterial angiography in the future.

Cerebral Angiography↗
PubMed2003

Magnetic resonance imaging at 3.0 Tesla: challenges and advantages in clinical neurological imaging.

MR imaging at very high field (3.0 T) is a significant new clinical tool in the modern neuroradiological armamentarium. In this report, we summarize our 40-month experience in performing clinical neuroradiological examinations at 3.0 T and review the relevant technical issues. We report on these issues and, where appropriate, their solutions. Issues examined include: increased SNR, larger chemical shifts, additional problems associated with installation of these scanners, challenges in designing and obtaining appropriate clinical imaging coils, greater acoustic noise, increased power deposition, changes in relaxation rates and susceptibility effects, and issues surrounding the safety and compatibility of implanted devices. Some of the these technical factors are advantageous (eg, increased signal-to-noise ratio), some are detrimental (eg, installation, coil design and development, acoustic noise, power deposition, device compatibility, and safety), and a few have both benefits and disadvantages (eg, changes in relaxation, chemical shift, and susceptibility). Fortunately solutions have been developed or are currently under development, by us and by others, for nearly all of these challenges. A short series of 1.5 T and 3.0 T patient images are also presented to illustrate the potential diagnostic benefits of scanning at higher field strengths. In summary, by paying appropriate attention to the discussed technical issues, high-quality neuro-imaging of patients is possible at 3.0 T.

Artifacts↗
PubMed2002

Effect of b value on contrast during diffusion-weighted magnetic resonance imaging assessment of acute ischemic stroke.

PURPOSE: To examine the effect of varying the diffusion encoding strength (b value) on the contrast (signal difference, Delta S) between damaged and normal tissue during diffusion-weighted magnetic resonance imaging (DWI) assessment of acute ischemic stroke. MATERIALS AND METHODS: Phantoms with diffusion values approximating those expected in acutely infarcted and normal tissue were constructed from a mixture of agar and formaldehyde and imaged at varying b values (0-3000 mm(-2) second). Ten patients were imaged with multiple b values (500-2500 mm(-2) second) within 12 hours of stroke onset. RESULTS: Theoretical calculations showed that for any combination of diffusion coefficients there existed an optimal b value that was higher than the standard setting of 1000 mm(-2) second, and this was confirmed by the phantom studies. In the patients, increasing b from 1000 to 1500 mm(-2) second increased Delta S (average, 22.4%; P = 0.001), but no consistent benefit was seen at b = 2000 mm(-2) second (P = 0.408). This compared favorably with the average optimal b value of 1662 mm(- 2) second calculated from the patients. CONCLUSION: These results suggest that increasing the b value from 1000 to 1500 mm(-2) second would increase contrast between infarcted and normal tissue in the setting of acute ischemic stroke.

Acute Disease↗
PubMed2002

Validation of injection parameters for catheter-directed intraarterial gadolinium-enhanced MR angiography.

RATIONALE AND OBJECTIVES: Catheter-directed intraarterial (IA) injections of gadolinium contrast agents may be used during endovascular interventions with magnetic resonance (MR) imaging guidance. Injection protocols require further validation. Using a flow phantom and swine, the authors aimed to (a) measure the optimal arterial gadolinium concentration ([Gd]) required for MR angiography and (b) validate a proposed IA injection protocol for gadolinium-enhanced MR angiography. MATERIALS AND METHODS: For in vitro experiments, the authors placed a catheter in the aorta of an aorto-renal-iliac flow phantom. Injected [Gd], injection rates, and aortic blood flow rates were varied independently for 36 separate IA gadolinium injections. The authors performed 2D and 3D MR angiography with a fast spoiled gradient-recalled echo sequence. For subsequent in vivo experiments, they selectively placed catheters within the aorta, renal artery, or common iliac artery of three pigs. Injection rate and injected [Gd] were varied. The authors performed 32 separate IA gadolinium injections for 2D MR angiography. Signal-to-noise ratios (SNRs) were compared for the various combinations of injection rate and injected [Gd]. RESULTS: In vitro, an arterial [Gd] of 2%-4% produced an optimal SNR for 2D MR angiography, and 3%-5% was best for 3D MR angiography. In swine, an arterial [Gd] of 1%-4% produced an optimal SNR. In the phantom and swine experiments, SNR was maintained at higher injection rates by inversely varying the injected [Gd]. CONCLUSION: Dilute arterial [Gd] is required for optimal IA gadolinium-enhanced MR angiography. To maintain an optimal SNR, injection rates and injected [Gd] should be varied inversely. The postulated injection protocol was validated.

Animals↗
PubMed2002

Time-resolved three-dimensional contrast-enhanced MR angiography of the peripheral vessels.

PURPOSE: To compare the diagnostic accuracy of time-resolved three-dimensional contrast material-enhanced magnetic resonance (MR) angiography with that of conventional angiography for imaging the lower extremity vasculature. MATERIALS AND METHODS: Sixty-nine patients who were evaluated for possible surgical intervention underwent conventional angiography (ie, digital subtraction angiography [DSA]) and contrast-enhanced MR angiography (ie, time-resolved imaging of contrast kinetics [TRICKS]). Two independent, blinded readers evaluated vessel stenosis and occlusion at DSA and MR angiographic image readings. Sensitivity, specificity, positive and negative predictive values, and area under the receiver operating characteristic curve were analyzed with repeated-measures analysis of variance. The Cohen kappa test was performed to examine interreader variability. RESULTS: At pooled readings, contrast-enhanced MR angiography had a sensitivity of 78% and a specificity of 98% for detection of occlusion. For detection of significant stenosis (at least one > or = 50% stenosis), sensitivity and specificity were 77% and 91%, respectively. Interreader agreement was high for detection of both occlusion (kappa = 0.76) and significant stenosis (kappa = 0.68). Sensitivity increased as MR angiographic technical parameters were optimized. When improvements resulting from coil type and injection protocol were considered, the sensitivity and specificity of TRICKS MR angiography were 89% and 97%, respectively, for occlusion detection and 87% and 90%, respectively, for significant stenosis detection. CONCLUSION: Contrast-enhanced TRICKS MR angiography is a feasible and minimally invasive means of acquiring angiograms of the peripheral vasculature with high sensitivity and specificity.

Adult↗
PubMed2002

Acute intravenous--intra-arterial revascularization therapy for severe ischemic stroke.

BACKGROUND: Intravenous alteplase for acute ischemic stroke is least efficacious for patients with proximal large-artery occlusions and clinically severe strokes. Intra-arterial therapy has the theoretical advantage of establishing a neurovascular diagnosis and high symptomatic artery patency rate but the disadvantage of requiring extra time and technical expertise. A combination of these two approaches may provide the best chance of improving outcome in severe acute ischemic stroke. We sought to assess the safety and feasibility of this approach. METHODS: This was a prospective, open-label study. Sequential patients arriving to our center within 3 hours of stroke onset who were treated with intravenous alteplase were screened for possible additional intra-arterial therapy using noninvasive neuroimaging. Clinical measures and outcomes were recorded prospectively. RESULTS: A total of 861 patients with ischemic stroke were admitted to Calgary hospitals during the study period. Eight patients over 21 months underwent a combined intravenous-intra-arterial approach. Six received intra-arterial alteplase and 1 underwent intracranial angioplasty; in a final patient, technical aspects prevented intra-arterial therapy. Early neurovascular and/or neurometabolic imaging identified the location of occlusion and tissue-at-risk (DWI-PWI mismatch) in all 8 patients. Two patients had a poor outcome, 1 patient suffered a significant groin hematoma, and there were no instances of symptomatic intracerebral hemorrhage. CONCLUSIONS: Intravenous followed by intra-arterial therapy is a promising approach to the treatment of severe acute ischemic stroke. Early noninvasive neurovascular and neurometabolic imaging is very helpful in choosing candidates for this type of therapy. On-going monitoring of alteplase-treated patients may allow the opportunity to perform rescue intra-arterial therapy.

Acute Disease↗
PubMed2002

Comparison of pre- and postcontrast 3D time-of-flight MR angiography for the evaluation of distal intracranial branch occlusions in acute ischemic stroke.

BACKGROUND AND PURPOSE: Three-dimensional time-of-flight (TOF) MR angiography is used routinely in stroke workup to detect arterial occlusions, but a major drawback is its inadequate depiction of vessels with slow or in-plane flow. We hypothesized that the use of contrast-enhanced MR angiography improves delineation of vessels with diminished or absent flow on precontrast MR angiograms. METHODS: Pre- and postcontrast 3D TOF MR angiograms were acquired in 55 consecutive patients with acute stroke. Patency of 480 intracranial vessels was assessed on both the pre- and postcontrast angiograms. Diffusion-weighted (DW) and perfusion-weighted (PW) imaging data were also obtained and results correlated with those of pre- and postcontrast MR angiography. RESULTS: For 50 abnormal vessel segments seen on precontrast MR angiograms, postcontrast MR angiograms resulted in change in the vascular signal intensity in 70% (35 vessel segments); 94% of these changes showed a greater extent of vessel patency. Venous and soft-tissue contrast enhancement had no effect on assessment in 95% of all 480 vessels examined. Interobserver reliability was moderate, with postcontrast interpretation (kappa = 0.48) showing a slight improvement over precontrast interpretation (kappa = 0.41). Good agreement was found between the TOF results and the pooled DW and PW imaging results. CONCLUSIONS: Compared with precontrast 3D TOF MR angiograms, postcontrast 3D TOF angiograms improve assessment of intracranial vessel patency in acutely ischemic vascular territories. In some patients, an improved understanding of acute ischemic stroke was obtained by viewing the pre- and postcontrast images. Postcontrast MR angiography should be included in the MR evaluation of acute stroke.

Acute Disease↗
PubMedDate not supplied

Differences between middle cerebral artery blood velocity waveforms of young and postmenopausal women.

OBJECTIVE: We characterized middle cerebral artery (MCA) blood flow velocity waveforms measured by transcranial Doppler ultrasonography in premenopausal (26.6 +/- 6.1 years, mean +/- SD) and postmenopausal (54.0 +/- 3.6 years) women, of whom six were receiving hormone therapy (PM-HT) and seven were not (PM-non-HT). We hypothesized that feature points on MCA waveforms are altered in postmenopausal women compared with those in young women. DESIGN: A short protocol involved maintaining end-tidal PO2 at euoxia (88 mm Hg) and end-tidal PCO2 at 1.5 mm Hg above eucapnic values using a dynamic end-tidal forcing system. Doppler data for the velocity spectral outline (Vp) were collected every 10 ms, and velocity waveform analyses were done on a beat-by-beat basis. Waveform features were identified over each cardiac cycle, including the average Vp (VCYC), maximum acceleration (AMAX), and the ratio of the velocity at the reflected wave and the velocity at peak systole (VR:VMAX). RESULTS: VCYC was unchanged between premenopausal and postmenopausal women (69.4 +/- 9.6 and 67.5 +/- 11.1 cm/s, respectively). AMAX was significantly higher (P = 0.007) in premenopausal women (987.9 +/- 280.7 cm/s) compared with postmenopausal women (743.1 +/- 100.3). Conversely, VR:VMAX was significantly smaller (P < 0.001) in premenopausal women (0.90 +/- 0.09) compared with postmenopausal women (1.11 +/- 0.05). In postmenopausal women, the reflected wave is higher than the maximum velocity at peak systole, suggesting the presence of a shoulder in the MCA waveform. CONCLUSIONS: Further investigations are required to assess whether this waveform analysis can provide insight into pathophysiologic changes in cerebral hemodynamics with aging.

Adult↗
PubMedDate not supplied

Fluid-attenuated inversion recovery preparation: not an improvement over conventional diffusion-weighted imaging at 3T in acute ischemic stroke.

BACKGROUND AND PURPOSE: Change in signal intensity due to acute ischemic stroke can be detected on diffusion-weighted (DW) images soon after symptom onset. Fluid-attenuated inversion recovery (FLAIR) DW imaging suppresses signal intensity from water and has been suggested to be better than conventional DW imaging as a diagnostic imaging technique in acute stroke. We compared the signal intensity-to-noise ratio (SNR) and contrast-to-noise-ratio (CNR) between ischemic and normal tissues by using these two sequences. METHODS: Twenty stroke patients underwent imaging less than 6 hours after stroke onset by using both acquisition methods. The SNR of six regions of interest in normal brain and one region in ischemic brain were compared on both DW imaging and FLAIR DW imaging. We also compared CNR in normal and ischemic tissues. The calculated apparent diffusion coefficient (ADC) maps from each acquisition technique were similarly assessed. RESULTS: The SNR was significantly lower for FLAIR DW imaging than for DW imaging (P < .05). The CNR between normal and ischemic tissue was also lower on FLAIR DW imaging (P < .05). SNR and CNR of the ADC maps were significantly different (P < .05) for all tissues except the putamen and white matter (for SNR and CNR) and globus pallidus (for CNR only). CONCLUSION: Ischemic tissue on FLAIR DW imaging was significantly less conspicuous than on DW imaging and potentially limits the clinical utility of this sequence.

Adult↗