3D Time-of-flight Research Articles

A systematic review of duplex ultrasound, magnetic resonance angiography and computed tomography angiography for the diagnosis and assessment of symptomatic, lower limb peripheral arterial disease

To determine the diagnostic accuracy and cost-effectiveness of duplex ultrasound (DUS), magnetic resonance angiography (MRA), and computed tomography angiography (CTA), as alternatives to contrast angiography (CA), for the assessment of lower limb peripheral arterial disease (PAD). Ten electronic databases were searched in April 2004, with an update in May 2005. Six key journals and bibliographies of included studies were also searched and experts in the field were consulted. Data extraction and quality assessment were performed in duplicate. Data were analysed according to test type and diagnostic threshold. For the economic analysis, a decision tree was developed and a probabilistic sensitivity analysis performed to incorporate statistical uncertainty into the cost-effectiveness analysis. A total of 113 studies met the inclusion criteria (including six economic evaluations). For the detection of stenosis greater than 50% in the whole leg, contrast-enhanced (CE) MRA (14 studies) had the highest diagnostic accuracy, with sensitivity ranging from 92 to 99.5% and specificity from 64 to 99%. Two-dimensional (2D) time-of-flight (TOF) MRA (11 studies) was less accurate, with sensitivity ranging from 79 to 94% and specificity from 74 to 92%. 2D phase-contrast (PC) MRA (one study) had a sensitivity of 98% and specificity of 74%. CTA (seven studies) also appeared slightly inferior to CE MRA, with a sensitivity ranging from 89 to 99% and specificity from 83 to 97%, but better than DUS (28 studies), which had a sensitivity ranging from 80 to 98% and specificity from 89 to 99%. There was some indication that CE MRA and DUS were more accurate for detecting stenoses/occlusions above the knee than below the knee or in the pedal artery. The four studies of patient attitudes strongly suggested that patients preferred CE MRA to CA. CA was considered the most uncomfortable test, followed by CE MRA, with CTA being the least uncomfortable. Half of the patients (from a sample who did not suffer from claustrophobia and had no metallic implants) expressed no preference between undergoing TOF MRA or DUS; most of those who did express a preference favoured TOF MRA. In the 55 studies identified for adverse events, MRA was associated with the highest reported proportion. However, the most severe adverse events were more common in patients undergoing CA; although these were rare for both tests. The economic evaluation showed DUS dominated the other alternatives when the whole leg was assessed, by presenting higher effectiveness at a lower cost per quality-adjusted life-year (QALY; i.e. 13,646 pounds per QALY). When the assessment was limited to a section of the leg, either above the knee or below the knee, 2D TOF MRA was the most cost-effective preoperative diagnostic strategy. The incremental cost per QALY for below-the-knee comparisons was equal to 37,024 pounds when 2D TOF MRA was compared with DUS. For above-the-knee comparisons, 2D TOF MRA presented the lowest cost and slightly lower effectiveness compared with CE MRA, with a cost per QALY equal to 13,442 pounds. The results of the review suggest that CE MRA has a better overall diagnostic accuracy than CTA or DUS, and that CE MRA is generally preferred by patients over CA. Where available, CE MRA may be a viable alternative to CA. The only controlled trial suggested that the results of DUS were comparable to those of CA, in terms of surgical planning and outcome. This finding conflicts with the results of diagnostic accuracy studies, which reported poor estimates of accuracy for DUS in comparison with CA. There was insufficient evidence to evaluate the usefulness of CTA for the assessment of PAD, particularly newer techniques. The results of the economic modelling suggest that for PAD patients for whom the whole leg is evaluated by a preoperative diagnostic test, DUS dominates the other alternatives by presenting higher effectiveness at a lower cost per QALY. However, when the analysis of stenosis is limited to a section of the leg, either above the knee or below the knee, 2D TOF MRA appears to be the most cost-effective preoperative diagnostic strategy. Further research is needed into a number of areas including the relative clinical effectiveness of the available imaging tests, in terms of surgical planning and postoperative outcome.

3 T Contrast-Enhanced Magnetic Resonance Angiography for Evaluation of the Intracranial Arteries

We sought to prospectively evaluate the image quality and visualization of the intracranial arteries using high spatial resolution contrast-enhanced magnetic resonance angiography (CE-MRA) at 3 T and to perform intraindividual comparison with time-of-flight (TOF) MRA and multislice CT angiography (CTA). Twelve patients (5 men, 7 women, 37-71 years of age) with suspected cerebrovascular disease prospectively underwent MRA and CTA. MRA was performed on a 3 T MR system, including both 3-dimensional (3D) TOF (Voxel dimension: 0.6 x 0.5 x 0.9 mm in 5 minutes and 40 seconds) and 3D CE-MRA (voxel dimension: 0.7 x 0.7 x 0.8 mm in 20 seconds, using parallel acquisition with an acceleration factor of 4). CTA images were acquired on a 16-slice CT scanner (voxel dimension: 0.35 x 0.35 x 0.8 mm in 17 seconds). The image quality and visualization of up to 26 intracranial arterial segments in each study was evaluated by 2 experienced radiologists. The arterial diameter for selective intracranial arteries was measured independently on each of the 3 studies, and statistical analysis and comparative correlation was performed. A total of 312 arterial segments were examined by CE-MRA, TOF-MRA, and CTA. The majority of intracranial arteries (87%) were visualized with diagnostic image quality on CE-MRA with a significant correlation to TOF (R values = 0.84; 95% confidence interval 0.79-0.86, P < 0.0001), and to CTA (R values = 0.74; 95% confidence interavl 0.68-0.78, P < 0.001). The image quality for small intracranial arteries, including the anterior-inferior cerebellar artery, the posterior communicating artery, and the M3 branch of the middle cerebral artery, was significantly lower on CE-MRA compared with TOF and CTA (P < 0.03). There was a significant correlation for the dimensional measurements of arterial diameters at CE-MRA with TOF (r = 0.88, 95% confidence interval 0.81-0.93), and CTA (r = 0.83, 95% confidence interval 0.73-0.90). The described 3 T CE-MRA protocol, spanning from the cervical to the intracranial vessels, visualized and characterized the majority of intracranial arteries with image quality comparable with that obtained using TOF-MRA and CTA. Further clinical studies are required to establish the accuracy of the technique in a broader clinical setting.

High relaxivity contrast agents in MR angiography of the carotid arteries

Magnetic Resonance Angiography (MRA) is one of the most practical diagnostic imaging modalities in the field of neurovascular imaging where risks associated with catheter angiography are high. Evaluation of the extracranial supraortic vessels, and in particular the carotid arteries, is the major field of application for MRA. Before the development of rapid contrast-enhanced (CE) acquisition sequences, the major limitations of MRA pertaining to the carotid arteries was the limited volume of study when 3D time-of-flight (TOF) images were acquired, and the saturation effects together with low spatial resolution and movement artifacts when 2D TOF images were acquired. Although technical improvements helped overcome some of these limitations, MRA was still not considered a valid diagnostic alternative to DSA for the evaluation of carotid artery stenosis until the advent of CE acquisitions. Most published studies on CE-MRA of the carotid arteries have been performed with standard gadolinium-based chelates which have similar r1 relaxivity values. Newer gadolinium chelates such as gadobenate dimeglumine (Multihance, Gd-BOPTA, Bracco) have higher intravascular r1 relaxivity than other agents such as Gd-DTPA. This leads to higher vascular peak enhancement of longer duration which has proven beneficial for improving vascular contrast. CE-MRA is today considered a highly suitable replacement for conventional MRA techniques and DSA for the evaluation of extracranial carotid artery disease. Compared with unenhanced MRA sequences, CE-MRA permits complete and reliable evaluation of the internal carotid artery from the bifurcation to the intracranial segment. Moreover, the technique offers better overall accuracy for the depiction of tight stenosis and more confident diagnosis of real carotid occlusion versus subocclusive stenosis.

Inflow Stenoses in Dysfunctional Hemodialysis Access Fistulae and Grafts

The aim of the study is to prospectively determine the incidence of inflow stenoses in dysfunctional hemodialysis access arteriovenous fistulae (AVFs) and grafts (AVGs). Contrast-enhanced magnetic resonance angiography (CE-MRA) was performed of 66 dysfunctional AVFs and 35 AVGs in 56 men and 45 women (mean age, 62 years; age range, 31 to 86 years). Complete inflow (from the subclavian artery), shunt region, and complete outflow (including subclavian vein) were shown at CE-MRA. In addition to standard digital subtraction angiography (DSA) of the shunt region and outflow, DSA of the complete inflow was obtained through access catheterization of all cases in which CE-MRA showed an inflow stenosis. Vascular stenosis is defined as greater than 50% decrease in luminal diameter compared with an uninvolved vascular segment located adjacent to the stenosis. Endovascular intervention of stenoses was performed in connection with DSA. CE-MRA showed 19 arterial stenoses in 14 patients (14%). DSA confirmed 18 of these lesions in 13 patients and showed no additional inflow lesions. Of the 13 patients, 7 patients had arterial stenoses only and 6 patients had accompanying stenoses in the shunt region and/or outflow. Referral criteria for the 13 patients to undergo access evaluation had been decreased flow rates (9 patients), steal symptoms (2 patients), and insufficient access maturation (2 patients). Access flow of the 9 patients with a low-flow access improved from 477 +/- 74 mL/min to 825 +/- 199 mL/min after angioplasty. One patient with steal symptoms became symptom free after angioplasty. Endovascular intervention in 3 patients proved to be unsuccessful. Inflow stenoses are not uncommon in dysfunctional hemodialysis access shunts. We suggest that radiological evaluation comprise assessment of the complete arterial inflow.

High‐resolution, time‐resolved MRA provides superior definition of lower‐extremity arterial segments compared to 2D time‐of‐flight imaging

To evaluate a novel time-resolved contrast-enhanced (CE) projection reconstruction (PR) magnetic resonance angiography (MRA) method for identifying potential bypass graft target vessels in patients with Class II-IV peripheral vascular disease. Twenty patients (M:F = 15:5, mean age = 58 years, range = 48-83 years), were recruited from routine MRA referrals. All imaging was performed on a 1.5 T MRI system with fast gradients (Signa LX; GE Healthcare, Waukesha, WI). Images were acquired with a novel technique that combined undersampled PR with a time-resolved acquisition to yield an MRA method with high temporal and spatial resolution. The method is called PR hyper time-resolved imaging of contrast kinetics (PR-hyperTRICKS). Quantitative and qualitative analyses were used to compare two-dimensional (2D) time-of-flight (TOF) and PR-hyperTRICKS in 13 arterial segments per lower extremity. Statistical analysis was performed with the Wilcoxon signed-rank test. Fifteen percent (77/517) of the vessels were scored as missing or nondiagnostic with 2D TOF, but were scored as diagnostic with PR-hyperTRICKS. Image quality was superior with PR-hyperTRICKS vs. 2D TOF (on a four-point scale, mean rank = 3.3 +/- 1.2 vs. 2.9 +/- 1.2, P < 0.0001). PR-hyperTRICKS produced images with high contrast-to-noise ratios (CNR) and high spatial and temporal resolution. 2D TOF images were of inferior quality due to moderate spatial resolution, inferior CNR, greater flow-related artifacts, and absence of temporal resolution. PR-hyperTRICKS provides superior preoperative assessment of lower limb ischemia compared to 2D TOF.

High-resolution Three-dimensional Magnetic Resonance Angiography and Three-dimensional Spoiled Gradient-recalled Imaging in the Evaluation of Neurovascular Compression in Patients with Trigeminal Neuralgia: A Double-blind Pilot Study

To assess the value of high-resolution three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography and gadolinium (Gad)-enhanced 3D spoiled gradient-recalled imaging in the visualization of neurovascular compression in patients with trigeminal neuralgia. Forty-eight patients with unilateral trigeminal neuralgia underwent high-resolution 3D TOF MR angiography. After administration of a contrast agent, a 3D spoiled gradient-recalled sequence (3D Gad) was run. Images were reviewed by a radiologist blinded to clinical details. All patients underwent microvascular decompression surgery. Microdissection of the trigeminal nerve and compressing vessels was videotaped during surgery and reviewed by surgeons uninvolved in patient care. Results from neuroradiological studies were then compared with findings on operative videotapes. MR angiography in combination with 3D Gad imaging identified surgically verified neurovascular contact in 42 of 46 (91%) symptomatic nerves. The offending vessel (artery, vein) was correctly identified in 31 of 41 cases (sensitivity, 76%; specificity, 75%). Neurovascular compression was observed in 71% of asymptomatic nerves with a trend toward greater compression severity on the symptomatic nerve (P < 0.09). Agreement between the direction of neurovascular contact defined by 3D TOF MR angiography and 3D Gad and findings at surgery was good (kappa = 0.78; 95% confidence interval, 0.61-0.94). Double-blind assessment of surgical and neuroradiological findings confirms that neurovascular compression can be visualized with good sensitivity in patients with trigeminal neuralgia by 3D TOF MR angiography in combination with Gad-enhanced 3D spoiled gradient-recalled sequences. Anatomic relationships defined by this method can be useful in predicting surgical findings.

Fast reconstruction of 3D time-of-flight PET data by axial rebinning and transverse mashing

Faster scintillators like LaBr3 and LSO have sparked renewed interest in PET scanners with time-of-flight (TOF) information. The TOF information adds another dimension to the data set compared to conventional three-dimensional (3D) PET with the size of the projection data being multiplied by the number of TOF bins. Here we show by simulations and analytical reconstruction that angular sampling for two-dimensional (2D) TOF PET can be reduced significantly compared to what is required for conventional 2D PET. Fully 3D TOF PET data, however, have a wide range of oblique and transverse angles. To make use of the smaller necessary angular sampling we reduce the 3D data to a set of 2D histoprojections. This is done by rebinning the 3D data to 2D data and by mashing these 2D data into a limited number of angles. Both methods are based on the most likely point given by the TOF measurement. It is shown that the axial resolution loss associated with rebinning reduces with improved timing resolution and becomes less than 1 mm for a TOF resolution below 300 ps. The amount of angular mashing that can be applied without tangential resolution loss increases with improved TOF resolution. Even quite coarse angular mashing (18 angles out of 324 measured angles for 424 ps) does not significantly reduce image quality in terms of the contrast or noise. The advantages of the proposed methods are threefold. Data storage is reduced to a limited number of 2D histoprojections with TOF information. Compared to listmode format we have the advantage of a predetermined storage space and faster reconstruction. The method does not require the normalization of projections prior to rebinning and can be applied directly to measured listmode data.

Comparison of 3.0- and 1.5-T Three-dimensional Time-of-Flight MR Angiography in Moyamoya Disease: Preliminary Experience

To prospectively compare 3.0- and 1.5-T three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography in patients with moyamoya disease, with special emphasis on the visualization of abnormal netlike vessels (moyamoya vessels). Study protocols were approved by the local ethics committee; written informed consent was obtained from all patients. The study included 24 consecutive patients with moyamoya disease (four male and 20 female patients). Patients ranged in age from 17 to 66 years (mean age, 41 years). Moyamoya disease had been diagnosed in all patients before they were entered into the study. All patients underwent 3D TOF MR angiography at both 3.0 and 1.5 T; imaging examinations were performed within 14 days of each other. Maximum intensity projections (MIPs) obtained with MR angiography performed at both 3.0 and 1.5 T were evaluated by two neuroradiologists; the visualization of moyamoya vessels was graded according to a 4-point scale. For both 3.0- and 1.5-T imaging, the number of high-signal-intensity areas and the summation of cross-sectional areas of high signal intensity on source images obtained at the same level of MR angiography were compared quantitatively by using the Wilcoxon matched-pair signed-rank test. Moyamoya vessels were better visualized on MIPs obtained with 3.0-T imaging than on MIPs obtained with 1.5-T imaging (P < .001). At the identical level of the source image, 3.0-T imaging depicted more high-signal-intensity areas than did 1.5-T imaging. Wider cross-sectional areas of moyamoya vessels were visualized with 3.0-T imaging than with 1.5-T imaging (P < .001). Moyamoya vessels are better depicted with MR angiography at 3.0 T than at 1.5 T.

Bright and black blood imaging of the carotid bifurcation at 3.0 T

Purpose The aim of this study was to evaluate our preliminary experience at 3.0 T with imaging of the carotid bifurcation in healthy and atherosclerotic subjects. Application at 3.0 T is motivated by the signal-to-noise gain for improving spatial resolution and reducing signal averaging requirements. Materials and methods We utilized a dual phased array coil and applied 2D, 3D time of flight (TOF) and turbo spin echo (TSE) sequences with comparison of two lumen signal suppression methods for black blood (BB) TSE imaging including double inversion preparation (DIR) and spatial presaturation pulses. The signal-to-noise ratios (SNR) of healthy carotid vessel walls were compared in 2D and 3D BB TSE acquisitions. The bright and black blood multi-contrast exam was demonstrated for a complex carotid plaque. Results Contrast-to-noise (CNR) greater than 150 was achieved between the lumen and suppressed background for 3D TOF. For BB, both methods provided sufficient lumen signal suppression but slight residual flow artifacts remained at the bifurcation level. As expected 3D TSE images had higher SNR compared to 2D, but increased motion sensitivity is a significant issue for 3D at high field. For multi-contrast imaging of atherosclerotic plaque, fibrous, calcified and lipid components were resolved. The CNR ratio of fibrous (bright on PDW, T2W) and calcified (dark in T1W, T2W, PDW) plaque components was maximal in the T2W images. The 3D TOF angiogram indicating a 40% stenosis was complemented by 3D multi-planar reformat of BB images that displayed plaque extent. Detection of intimal thickening, the earliest change associated with atherosclerotic progression was observed in BB PDW images at 3.0 T. Conclusions High SNR and CNR images have been demonstrated for the healthy and diseased carotid. Improvements in RF coils along with pulse sequence optimization, and evaluation of endogenous and exogenous contrast mechanisms will further enhance carotid imaging at 3.0 T.

Optimization of Three-dimensional Time-of-Flight Magnetic Resonance Angiography of the Intracranial Arteries

The signal-to-noise ratio obtained from arteries in three-dimensional (3D) time-of-flight (TOF) magnetic resonance (MR) angiography is often too low to allow clinical diagnosis because the radiofrequency pulse decreases the magnetization of protons in the blood and suppresses the in-flow effect in the slab. The present study adjusted the position of the head coil to boost arterial signal intensity. Ten healthy volunteers, eight men and two women aged 24-78 years, underwent 3D TOF MR angiography of the intracranial arteries with the same standard GE transmit-receive birdcage head coil using both normal and half position (lower edge of the coil level with the mouth) methods. Our subjects were divided into Group 1 consisted of five relatively young volunteers aged 24-42 years (mean 31.2 years), and Group 2 consisted of five older volunteers aged 70-78 years (mean 73 years). The following four arteries were chosen for analysis: the internal carotid artery (ICA), the proximal middle cerebral artery segment (M1), and the two distal middle cerebral artery segments (M2, M31). The half position method increased the signal-to-noise ratio in the ICA, M1, M2, and M3 by 15%, 25%, 36%, and 44%, respectively. In general, this method resulted in the generation of stronger signals in the M2 and M3 in younger subjects and in all arteries examined in older subjects. The half position method can provide better MR angiograms in certain brain regions of younger people, and in all brain regions in older patients.

Fluid–attenuated inversion recovery (FLAIR) sequences for the assessment of acute stroke

Diffusion-weighted magnetic resonance (MR) imaging (DWI), and three-dimensional (3D) time-of-flight (TOF) MR angiography (MRA), are highly sensitive for the early detection of stroke and arterial occlusion. However, only a few studies have evaluated the sensitivity of conventional MR sequences that are usually included in the imaging protocol. The aim of this study was to evaluate interobserver and intertechnique reproducibility of Fluid-Attenuated Inversion Recovery (FLAIR) sequences for the diagnosis of early brain ischemia and arterial occlusion. Over a 30-month period, brain MR examinations were performed in 34 patients within 12 hours after stroke onset. Imaging protocol included FLAIR sequences, DWI and 3D TOF MRA. Ten observers including radiologists and neurologists, performed separately a visual interpretation of FLAIR images for the detection of brain ischemia and arterial occlusion seen as an arterial high signal. DWI and 3D TOF MRA were used as reference and interpreted independently by two senior radiologists. Interobserver agreement was assessed for image quality, detectability and conspicuity of lesions whereas intertechnique agreement was only judged for lesion detectability. On FLAIR sequences, interobserver agreement for the detection of brain ischemia and arterial occlusion was excellent (kappa = 0.81 and 0.87 respectively). The concordance between FLAIR and DWI sequences for the detection of brain ischemia and between FLAIR and 3D TOF MRA for the detection of arterial occlusion were judged as excellent for all observers (kappa = 0.91 and 0.89 respectively). Although DWI is the most sensitive technique with which to detect acute stroke, FLAIR imaging may also be useful to demonstrate both acute ischemia and arterial occlusion with an excellent interobserver reproducibility.

Preoperative evaluation of venous systems with 3-dimensional contrast-enhanced magnetic resonance venography in brain tumors: comparison with time-of-flight magnetic resonance venography and digital subtraction angiography

Background Recent developments in magnetic resonance (MR) technology now enable the use of MR venography, providing 3-dimensional (3D) images of intracranial venous structures. The purpose of this study was to assess the usefulness of 3D contrast-enhanced MR venography (CE MRV) in the evaluation of intracranial venous system for surgical planning of brain tumors. Methods Forty patients underwent 3D CE MRV, as well as 25 patients, 2-dimensional (2D) time-of-flight (TOF) MR venography in axial and sagittal planes; and 10 patients, digital subtraction angiography. We determined the number of visualized sinuses and cortical veins. Degree of visualization of the intracranial venous system on 3D CE MRV was compared with that of 2D TOF MR venography and digital subtraction angiography as a standard. We also assessed the value of 3D CE MRV in the investigation of sinus occlusion or localization of cortical draining veins preoperatively. Results Superficial cortical veins and the dural sinus were better visualized on 3D CE MRV than on 2D TOF MR venography. Both MR venographic techniques visualized superior sagittal sinus, lateral sinus, sigmoid sinus, straight sinus, and internal cerebral vein and provided more detailed information by showing obstructed sinuses in brain tumors. Only 3D CE MRV showed superficial cortical draining veins. However, it was difficult to accurately evaluate the presence of cortical collateral venous drainage. Conclusion Although we do not yet advocate MR venography to replace conventional angiography as the imaging standard for brain tumors, 3D CE MRV can be regarded as a valuable diagnostic method just in evaluating the status of major sinuses and localization of the cortical draining veins.

Carotid Artery Stenosis: Intraindividual Correlations of 3D Time-of-Flight MR Angiography, Contrast-enhanced MR Angiography, Conventional DSA, and Rotational Angiography for Detection and Grading

To compare three-dimensional (3D) time-of-flight (TOF) MR angiography, contrast-enhanced MR angiography, digital subtraction angiography (DSA), and rotational angiography for depiction of stenosis. The study had Ethics Committee approval, and each patient gave written informed consent. Forty-nine patients (18 women, mean age, 67.2 years +/- 9.1 [+/- standard deviation], and 31 men, mean age, 63.1 years +/- 8.0) with symptomatic stenosis of internal carotid artery (ICA) diagnosed at duplex ultrasonography underwent transverse 3D TOF MR angiography with sliding interleaved kY acquisition and coronal contrast-enhanced MR angiography, followed by DSA and rotational angiography within 48 hours. MR angiography was performed at 1.5-T with a cervical coil. Contrast-enhanced MR angiograms were obtained after a bolus injection of 20 mL of gadobenate dimeglumine. Maximum ICA stenosis on maximum intensity projection and source images was quantified according to NASCET criteria. Correlations for 3D TOF MR angiography, contrast-enhanced MR angiography, DSA, and rotational angiography were determined by means of cross tabulation, and accuracy for detection and grading of stenoses were calculated. Data were evaluated with analysis of variance, Wilcoxon signed rank test, and McNemar test, all at significance of P < .05. Ninety-eight ICAs were evaluated at contrast-enhanced MR angiography, DSA, and rotational angiography, and 97 were evaluated at 3D TOF MR angiography. Correlations for contrast-enhanced MR angiography, 3D TOF MR angiography, and DSA relative to rotational angiography were r2 = 0.9332, r2 = 0.9048, and r2 = 0.9255, respectively. Lower correlation (r2 = 0.8593) was noted for contrast-enhanced MR angiography and DSA. Respective sensitivity and specificity for detection of hemodynamically relevant stenosis relative to rotational angiography were 100% and 90% for contrast-enhanced MR angiography, 95.5% and 87.2% for 3D TOF MR angiography, and 88.6% and 100% for DSA. Four of 31 severe stenoses were underestimated at DSA, and three were underestimated at contrast-enhanced MR angiography. Three severe stenoses were underestimated at 3D TOF MR angiography, and one was misclassified as occluded. Of 13 moderate (50%-69%) stenoses, one was overestimated at contrast-enhanced MR angiography, two were underestimated and three overestimated at 3D TOF MR angiography, and two were underestimated at DSA. DSA results in an underestimation of ICA stenosis compared with rotational angiography. Contrast-enhanced MR angiography correlates best with rotational angiography.

Surveillance of intracranial aneurysms treated with detachable coils: a comparison of MRA techniques

Two MRA techniques were evaluated for the follow-up of coiled intracranial aneurysms. Twenty-nine coiled aneurysms were evaluated for a total of 36 follow-up assessments using 3D time-of flight MRA (TOF MRA), an auto-triggered elliptic-centric-ordered three-dimensional gadolinium-enhanced MR angiogram (ATECO MRA), as well as a selective digital subtraction angiography (DSA), which served as the "gold standard". Confident visualization was seen in 36 (100%) of ATECO MRAs and in 32 (89%) of the TOF MRAs. Eleven residual aneurysm components (RACs) greater than 2 mm were described on DSA. Of these, nine were seen on ATECO MRA (sensitivity of 81% and specificity of 88%) and four were seen on TOF MRA (sensitivity of 40% and specificity of 90%). The two RACs not seen on ATECO MRA both measured 3 mm. The six RACs not seen on TOF MRA measured 3, 4 and 5 mm. ATECO MRA provides a non-invasive reliable angiogram for the surveillance of coiled aneurysms and is superior to TOF MRA for this purpose.

Fourier rebinning of time-of-flight PET data

This paper explores fast reconstruction strategies for 3D time-of-flight (TOF) positron emission tomography (PET), based on 2D data rebinning. Starting from pre-corrected 3D TOF data, a rebinning algorithm estimates for each transaxial slice the 2D TOF sinogram that would have been acquired by a single-ring scanner. The rebinned sinograms can then be reconstructed using any algorithm for 2D TOF reconstruction. We introduce TOF-FORE, an approximate rebinning algorithm obtained by extending the Fourier rebinning method for non-TOF data. In addition, we identify two partial differential equations that must be satisfied by consistent 3D TOF data, and use them to derive exact rebinning algorithms and to characterize the degree of the approximation in TOF-FORE. Numerical simulations demonstrate that TOF-FORE is more accurate than two different TOF extensions of the single-slice rebinning method, and suggest that TOF-FORE will be a valuable tool for practical TOF PET in the range of axial apertures and time resolutions typical of current scanners.

Presence of Intraplaque Hemorrhage Stimulates Progression of Carotid Atherosclerotic Plaques

Previous studies suggest that erythrocyte membranes from intraplaque hemorrhage into the necrotic core are a source of free cholesterol and may become a driving force in the progression of atherosclerosis. We have shown that MRI can accurately identify carotid intraplaque hemorrhage and precisely measure plaque volume. We tested the hypothesis that hemorrhage into carotid atheroma stimulates plaque progression. Twenty-nine subjects (14 cases with intraplaque hemorrhage and 15 controls with comparably sized plaques without intraplaque hemorrhage at baseline) underwent serial carotid MRI examination with a multicontrast weighted protocol (T1, T2, proton density, and 3D time of flight) over a period of 18 months. The volumes of wall, lumen, lipid-rich necrotic core, calcification, and intraplaque hemorrhage were measured with a custom-designed image analysis tool. The percent change in wall volume (6.8% versus -0.15%; P=0.009) and lipid-rich necrotic core volume (28.4% versus -5.2%; P=0.001) was significantly higher in the hemorrhage group than in controls over the course of the study. Furthermore, those with intraplaque hemorrhage at baseline were much more likely to have new plaque hemorrhages at 18 months compared with controls (43% versus 0%; P=0.006). Hemorrhage into the carotid atherosclerotic plaque accelerated plaque progression in an 18-month period. Repeated bleeding into the plaque may produce a stimulus for the progression of atherosclerosis by increasing lipid core and plaque volume and creating new destabilizing factors.

Utility of contrast-enhanced 3D turbo-flash MR angiography in evaluating the intracranial venous system

The objective of this study was to compare the effectiveness of contrast-enhanced 3D turbo-flash and 2D time-of-flight (TOF) magnetic resonance angiography (MRA) sequences in the visualization and evaluation of the intracranial venous system. A prospective study was carried out on 41 patients referred to our Magnetic Resonance Imaging (MRI) unit with clinical findings suggestive of dural sinus thrombosis. Contrast-enhanced 3D turbo-flash and 2D TOF MRA sequences were performed, and the dural sinuses and cerebral veins were classified into five grades according to the quality of visualization and presence of thrombosis. We found the dural sinuses and cerebral veins to be normal in all sequences in 31 patients. Thrombosis of dural sinuses was detected in ten patients, with four of these ten cases found only in the contrast-enhanced 3D turbo-flash sequence. In general, complete visualization of cerebral veins and dural sinuses was significantly better accomplished with contrast-enhanced 3D turbo-flash MRA than with 2D TOF in either coronal or sagittal/oblique planes. Although 2D TOF MRA may be superior in detecting chronic dural sinus thrombosis, contrast-enhanced 3D turbo-flash MRA sequences may offer advantages for the early diagnosis and management of acute and subacute dural sinus thrombosis.

Avaliação da aterosclerose carotídea por intermédio de ultra-sonografia e ressonância magnética

OBJETIVO: Identificar ateromas carotídeos em coronariopatas com indicação de terapia cirúrgica. Avaliar o grau de estenose das artérias carótidas internas por meio de ultra-sonografia com Doppler colorido (UDC) e angiografia por ressonância magnética (ARM). Comparar a ecogenicidade das placas visualizadas pela ultra-sonografia (US), com a intensidade de sinal nos exames de ressonância magnética (RM). Avaliar a qualidade de imagens e confiabilidade interobservadores nos exames de RM. MATERIAIS E MÉTODOS: Estudo prospectivo em 50 pacientes. Utilizamos US e RM em seqüências ponderadas em T1 e T2, ambas pelas técnicas "black-blood" (BB) e "fat sat black-blood" (FSBB), e ARM 3D TOF ("time-of-flight'') com e sem contraste paramagnético. RESULTADOS: Do total de 100 segmentos, 81% apresentaram estenose pela US. Em 72 placas com ecogenicidade tipo 4 houve aumento da intensidade de sinal em 59,7% em T1-BB, 65,3% em T1-FSBB, 62,5% em T2-BB e 66,7% em T2-FSBB. Nas placas tipo 2 houve aumento da intensidade de sinal em 71,4% em T1-BB e T1-FSBB, 85,7% em T2-BB e 71,4% em T2-FSBB. Nas placas tipo 1 houve aumento da intensidade de sinal em 50,0% em T1 e T2. Em 19 segmentos a US foi considerada normal. Quando estes segmentos foram avaliados pela RM, houve aumento da intensidade de sinal em 47,4% em T1-BB, 57,9% em T1-FSBB e 52,6% em T2-BB e T2-FSBB. CONCLUSÃO: Houve alta incidência de aterosclerose carotídea. Houve reprodutibilidade marginal na associação entre o grau de estenose visualizado pela UDC e ARM. Não houve correlação entre os tipos de ecogenicidade das placas visualizadas pela US com as alterações de intensidade de sinal pela RM. A qualidade de imagens dos exames de RM foi considerada ótima em T1 e T2 e muito boa em 3D TOF (axial). A qualidade de imagem dos exames de ARM foi excelente. Notou-se ótima reprodutibilidade interobservadores, com valores de índice kappa acima de 0,71.

頚動脈血栓内膜剥離術におけるＭＲＡによる術前側副血行路の評価と術中脳波変化との関係

We retrospectively evaluated the relationship between the collateral pathway defined 3D Time-of Flight Magnetic Resonance Angiogram (MRA) and intraoperative cerebral ischemia. As the collateral pathway, ACA collateral and PCA collateral were defined and analyzed. Intraoperative cerebral ischemia was assessed by the continuously monitored electroencephalographic (EEG) change. Internal shunt was inserted routinely. Carotid stump pressure (CSP) was measured through the inserted shunt on all cases. In the cases except for contralateral carotid occlusion (n=100), incomplete pattern on both ACA collateral and PCA collateral was significantly related to the EEG change and CSP≤25 mmHg (p=0.003, p<0.0001, respectively). Individual evaluations showed the state of ACA collateral was significantly related to the EEG change and CSP≤25 mmHg (p=0.0025, p<0.0001, respectively). Conversely, the state of PCA collateral was not significantly related to them. Therefore, ACA collateral was a major pathway on carotid clamping except for the contralateral carotid occlusion case. Contralateral carotid occlusion (n=10) was significantly related to the EEG change and CSP≤25 mmHg (p<0.0001, p=0.0007, respectively), but no specific pattern of the collateral pathway related to them was found. Incomplete pattern on ACA collateral and contralateral carotid occlusion might predict intraoperative cerebral ischemia.

Utility of Source Images of Three-Dimensional Time-of-Flight Magnetic Resonance Angiography in the Diagnosis of Indirect Carotid-Cavernous Sinus Fistulas

We sought to assess the relative contribution of magnetic resonance imaging (MRI), maximum intensity projection (MIP), and source images of three-dimensional (3D) time-of-flight (TOF) magnetic resonance angiography (MRA) to the diagnosis of indirect (dural) carotid-cavernous sinus fistulas (CCFs). MRI and 3D TOF MRA were obtained in eight consecutive patients with indirect CCFs confirmed by conventional catheter angiography. Two radiologists masked to the angiographic results reviewed images retrospectively to evaluate the efficacy of MRI and 3D TOF MRA source and MIP images in the diagnosis of CCF. MRI disclosed CCF in five of eight cases; MIP images of TOF MRA disclosed CCF in four cases; source images of TOF MRA disclosed all eight CCF cases. The MRA source images are indispensable for a confirmatory diagnosis of indirect (dural) CCF. Underdiagnosis may occur by relying on MRI or 3D TOF MIP images alone.