Regional CBF changes in Parkinson’s disease: a correlation with motor dysfunction

Purpose The purpose of this study was to further localize cerebral perfusion abnormalities, and to better correlate these abnormalities with the clinical severity of Parkinson’s disease (PD). Methods A single-photon emission computed tomography (SPECT) study was performed on 27 patients with PD and 24 age-matched controls. SPECT images were spatially normalized, concatenated, and then decomposed using Infomax independent component analysis (ICA). The resulting image components were separated by logistic regression into two subspaces: “disease-related” components whose subject weights differed between groups, and “disease-unrelated” components. The resultant regional cerebral blood flow (rCBF) subspace images were normalized to global CBF for each subject, and then processed using statistical parametric mapping to compare rCBF values between PD and control subjects. Results In the disease-related image subspace, patients with PD exhibited significantly higher adjusted rCBF in the putamen, globus pallidum, thalamus, brainstem, and the anterior lobe of the cerebellum, and significant hypoperfusion in the parieto-temporo-occipital cortex, the dorsolateral prefrontal cortex, the insula, and the cingulate gyrus. The motor Unified Parkinson’s Disease Rating Scale scores correlated negatively with rCBF in the insula and cingulate gyrus. In the disease-unrelated image subspace, no brain voxels exhibited a significant group difference. Conclusion ICA-based separation of normalized images into disease-related and disease-unrelated subspaces revealed many disease-related group blood flow differences. The regions revealed by ICA are consistent with the current model of PD. These rCBF changes in PD have not been fully demonstrated in any single functional imaging study previously. An editorial commentary on this paper is available at     

Brain perfusion measured by flow-sensitive alternating inversion recovery (FAIR) and dynamic susceptibility contrast-enhanced magnetic resonance imaging: comparison with nuclear medicine technique

The aim of this study was to compare cerebral perfusion images and regional cerebral blood flow (rCBF) of SPECT study with the images and regional intensity of relative cerebral blood flow (CBF) images acquired by contrast-enhanced perfusion MR imaging (pMRI) and flow-sensitive alternating inversion recovery (FAIR). Twelve patients with various cerebral diseases were underwent I-123-IMP SPECT, pMRI, and FAIR studies to measure rCBF. A total of 12 regions of interest (ROI) were created over cerebrum and cerebellum to acquire the corresponding rCBF from I-123-IMP study and regional average signal intensity from CBF images of pMRI and FAIR studies. Left-to-right (L/R) and cerebral-to-cerebellar (CCR) ratios were created from the rCBF of I-123-IMP and signal intensity of CBF images of pMRI and FAIR. Image quality of FAIR was the poorest among all; however, CBF images of pMRI and FAIR images show comparatively decreased intensity at the corresponding site of decreased perfusion on I-123-IMP images. Both FAIR and pMRI images showed high intensity along the sinuses, choroid plexus, and large vessels in sulci. No significant correlation was found among all imaging modalities. But L/R ratio of I-123-IMP showed significant correlation with those of pMRI and FAIR, but for CCR, significant correlation was observed only between I-123-IMP and FAIR. Perfusion images of both pMRI and FAIR may produce images comparable to SPECT study. But to calculate absolute CBF more easy-to-apply and accurate algorithms are needed to overcome the artifacts from large vessels. Received: 25 January 2000 Revised: 7 June 2000 Accepted: 8 June 2000     

Comparative study of regional cerebral blood flow images by SPECT using xenon-133, iodine-123 IMP, and technetium-99m HM-PAO

Regional cerebral blood flow (rCBF) was measured by single photon emission computed tomography (SPECT) using 133Xe, N-isopropyl-p-[123I]iodoamphetamine ([123I]IMP) and [99mTc] hexamethylpropyleneamine oxime ([99mTc]HM-PAO) in 24 patients with cerebrovascular diseases. The greatest advantage of 133Xe SPECT was to be able to provide absolute rCBF values without arterial sampling. However, its image quality was very poor. Iodine-123 IMP SPECT provided rCBF images of higher quality and it had good correlation to 133Xe SPECT. Iodine-123 IMP SPECT provided the best images to detect mild ischemic lesions. It could detect obstructive or stenotic changes of large cerebral arteries very well except for a moderate stenosis of internal carotid artery. Technetium-99m HM-PAO SPECT also provided very good rCBF images and it had good correlation to 133Xe SPECT. However, the count-density ratios for the ischemic lesions to the contralateral presumed normal areas of [99mTc] HM-PAO SPECT were significantly higher than those of [123I]IMP SPECT.     

Measurement of cerebral hemodynamics with perfusion-weighted MR imaging: comparison with pre- and post-acetazolamide 133Xe-SPECT in occlusive carotid disease

BACKGROUND AND PURPOSE: We generated regional cerebral blood volume (rCBV) and regional cerebral blood flow (rCBF) studies from dynamic susceptibility contrast-enhanced MR images after an intravenous bolus injection of contrast agent (perfusion-weighted imaging [PWI]) by applying indicator dilution theory. We used a multishot echo-planar imaging (EPI) sequence to obtain adequate arterial input function (AIF). Our purpose was to compare the cerebral hemodynamics measured by PWI with the rCBF values and cerebral perfusion reserve obtained by xenon-133 single-photon emission CT (133Xe-SPECT). METHODS: Eight patients with chronic internal carotid artery occlusion or stenosis were examined. PWI data were acquired using a multishot EPI sequence, and the AIF was determined automatically. Our procedure was based on indicator dilution theory and deconvolution analysis. To eliminate the effect of superficial vessels, the automatic threshold selection method was used. RESULTS: AIF was adequate to generate rCBF and rCBV images. The rCBF and rCBV images by PWI were superior to 133Xe-SPECT scans in spatial resolution, and the rCBF values obtained by PWI correlated well with those obtained by 133Xe-SPECT. The regions with severely decreased perfusion reserve, which were determined by pre- and post-acetazolamide 133Xe-SPECT, showed significantly lower rCBF and higher rCBV by PWI than did regions with normal and moderately decreased perfusion reserve. CONCLUSION: The rCBF and rCBV images generated by our procedure using PWI data appear to provide important clinical information for evaluating the degree of cerebral perfusion reserve impairment in patients with chronic ischemia.     

Transoral ultrasonographic evaluation of carotid flow in predicting cerebral hemodynamics after carotid endarterectomy

PURPOSE: We investigated whether measurement of blood flow in the extracranial distal internal carotid artery (ICA) by transoral carotid ultrasonography (TOCU) can predict the cerebral hemodynamics and the hemodynamic effect of carotid endarterectomy (CEA) in patients with unilateral carotid stenosis. METHODS: Forty-nine patients with unilateral ICA stenosis who underwent CEA were studied. Preoperative blood flow in the poststenotic portion of the extracranial ICA was studied by using TOCU. Regional cerebral blood flow (rCBF) and vasoreactivity to acetazolamide (VR) in the territory of the middle cerebral artery were investigated by using single-photon emission CT (SPECT) before, 2 weeks after, and 3 months after CEA. RESULTS: Doppler flow velocities in the extracranial distal ICA measured transorally by TOCU correlated with baseline as well as postacetazolamide rCBF in the ipsilateral side (regression analysis, P < .05). Diameter and blood flow volume in the extracranial distal ICA were associated with ipsilateral postacetazolamide rCBF and VR (regression analysis, P < .05). When the patients were divided into 2 groups according to the ICA volume flow distal to a carotid stenosis, group I < 3.5 mL/s and group II > 3.5 mL/s, ipsilateral postacetazolamide rCBF in group I was significantly lower than that in group II (P = .008). Ipsilateral postacetazolamide rCBF (analysis of variance [ANOVA], P = .02) and VR (ANOVA, P = .03) significantly improved after CEA for 3 months in group I but not in group II. CONCLUSION: TOCU can detect the decrease in poststenotic flow of the distal extracranial ICA that is indicative of impaired intracranial hemodynamics and predictive for improvement of cerebral blood flow after CEA in patients with unilateral carotid stenosis.     

早期梅毒患者的脑血流灌注显像

目的评价早期梅毒对中枢神经系统的影响。方法53例早期梅毒患者行^99Tc^m-双半胱乙酯(ECD)脑血流灌注显像，通过目测视觉分析判断脑血流灌注异常部位。结果53例患者的显像结果分为5种类型。其中48例存在不同程度的脑血流灌注异常，大脑前、中动脉分布区受累部位明显多于椎-基底动脉分布区。结论梅毒螺旋体早期即可侵入中枢神经系统。     

Isotropic CT examination of abdomen and pelvis diagnostic quality of reformat

RATIONALE AND OBJECTIVES: To evaluate the image quality of axial and coronal reformats obtained from isotropic resolution abdomino-pelvic computed tomography (CT) examinations. MATERIALS AND METHODS: Thirty consecutive patients with intravenous contrast-enhanced abdomino-pelvic CT examinations (Brilliance 40, Philips Medical Systems, Cleveland, OH) were enrolled for the study. The raw data were reconstructed into two sets of source axial images: 0.9-mm slice widths with 0.45-mm reconstruction interval (isotropic resolution) and 4-mm slice widths with 3-mm reconstruction interval (anisotropic resolution: group A). Isotropic data set was reformatted into axial and coronal stacks (groups B and C, respectively) with 4-mm slice width and 3-mm interval. Three independent readers evaluated stacks A to C using a 3-point scale for resolution of hepatic vessels, edge sharpness of kidneys, respiratory motion artifact, reconstruction artifact, noise, and overall image quality. RESULTS: There was no statistical difference among the groups A to C for vessel resolution, motion artifact, noise, and overall quality. The scores given to group C were significantly lower than those to groups A and B for reconstruction artifacts. There was no difference among groups A to C for overall impression of image quality. The interreader agreements were excellent for axial images (groups A and B) and moderate for coronal reformats. CONCLUSION: Isotropic scanning of the abdomen and pelvis allows creation of reformats with similar image quality as similar thickness axial source images. These reformats are of sufficient quality to form the basis of clinical interpretation.     

双源CT双能量去骨技术在头颈部血管成像中的应用

目的：比较双能量去骨与减影去骨对头颈部血管CT成像（CTA）的差异,探讨头颈部双能量CT血管成像（DECTA）的应用价值。方法：50例患者行DECTA检查并行双能量去骨,对照组45例患者使用减影CTA检查并去骨,然后分别比较DECTA和减影CTA的图像质量、去骨所用时间及放射剂量,并观察DECTA上颈总动脉分叉处钙化的显示效果。结果：颅内动脉DECTA和减影CTA的图像质量差异无显著性意义（Z=0.790,P=0.430）,颈内动脉虹吸段和岩段DECTA图像质量优于减影CTA（虹吸段Z=-1.989,P=0.047;岩段Z=-2.014,P=0.044）,而减影CTA显示颈根部动脉优于DECTA（Z=3.900,P〈0.001）。同时DECTA减少约24.0%的放射剂量。DECTA上共有28例发现有血管性病变,所有病变显示清晰,其中10例并与DSA或外科手术对照具有良好的一致性。颈总动脉分叉处36个钙化灶中有8个钙化灶未在DECTA上显示。结论：DECTA显示头颈部血管总体良好,成功率高,且放射剂量明显减少,但对于颈根部动脉显示仍存在一定局限。     

Effect of vascular radioactivity on regional values of cerebral blood flow: evaluation of methods for H(2)(15)O PET to distinguish cerebral perfusion from blood volume.

To evaluate the appropriate model for calculating regional cerebral blood flow (rCBF) with PET and H(2)(15)O, the values obtained from 1- and 2-compartment analyses were compared. METHODS: Dynamic PET scans were performed on 12 healthy volunteers after injection of H(2)(15)O in 2 conditions of baseline and visual stimulation. Calculation of rCBF was performed using the 2-weighted integral (WI) and autoradiographic methods for the 1-compartment analysis, and the 3-WI method was followed for the 2-compartment analysis. Arterial blood radioactivity was counted continuously and corrected for delay and dispersion. The rCBF images were transformed into the Talairach space and analyzed by statistical parametric mapping to identify regional differences in the 2 methods. The values obtained from regions of interest also were compared. RESULTS: Although the difference in global CBF between the 2 models was not significant, rCBF values in the large arteries and neighbor areas were significantly greater in the 2-WI method than in the 3-WI method. However, regional differences in the activation studies were not affected when the 2 methods were compared. The images of cerebral arterial blood volume (V(0)) obtained by the 3-WI method showed a significant increase in V(0) in the visual cortex during visual stimulation. CONCLUSION: These results suggest that the rCBF values in the 1-compartment analysis were affected by radioactivity in the vessels. The 3-WI method could provide rCBF values that are less influenced by vascular radioactivity and also show differences in V(0) in PET activation studies.     

Assessing tissue viability with MR diffusion and perfusion imaging

BACKGROUND AND PURPOSE: Diffusion- (DW) and perfusion-weighted (PW) MR imaging reflect neurophysiologic changes during stroke evolution. We sought to determine parameters that distinguish regions of brain destined for infarction from those that will survive despite hypoperfusion. METHODS: DW and PW images were obtained in 30 patients at 1-12 hours after symptom onset. Relative cerebral blood volume (rCBV), flow (rCBF), mean transit time (MTT), apparent diffusion coefficient (ADC), DW image signal intensity, and fractional anisotropy (FA) lesion-contralateral normal region ratios were obtained in the following regions: 1) infarct core with hyperintensity on DW image, abnormality on rCBF and MTT images, and follow-up abnormality; 2) infarcted penumbra with normal DW image, abnormal rCBF and MTT images, and follow-up abnormality; and 3) hypoperfused tissue that remained viable, with normal DW image, abnormal rCBF and MTT images, and normal follow-up. RESULTS: rCBF ratios for regions 1, 2, and 3 were 0.32 +/- 0.11, 0.46 +/- 0.13, and 0.58 +/- 0.12, respectively, and were significantly different. DW image intensity and ADC ratios were significantly different among all regions, but were more similar than rCBF ratios. rCBV and FA ratios were not significantly different between regions 2 and 3. No MTT ratios were significantly different. No region of interest with an rCBF ratio less than 0.36, an rCBV ratio less than 0.53, an ADC ratio less than 0.85, a DW image intensity ratio greater than 1.23, or an FA ratio greater than 1.10 remained viable. No region of interest with an rCBF ratio greater than 0.79 infarcted. CONCLUSIONS: Differences among mean ratios of three regions investigated were greatest for the rCBF ratio. The rCBF ratio may be the most useful parameter in differentiating viable tissue that is likely to infarct without intervention, from tissue that will survive despite hypoperfusion. ADC, DW intensity, FA, and rCBV ratios may provide adjunctive information.     

白质疏松病人局部脑血流变化的初步研究

为探讨白质疏松（ＬＡ）病人ＬＡ区域和皮质部位的局部脑血流（ｒＣＢＦ）变化及与痴呆的关系，对２４例伴有ＬＡ〔ＬＡ（＋）〕、２５例无ＬＡ〔ＬＡ（－）〕的皮质下多发性脑梗塞病人及１０例正常对照者行脑血流ＳＰＥＣＴ显像，并与智能评分进行相关分析。结果：ＬＡ（＋）组与正常组相比，额叶、颞叶、顶叶、ＬＡ区域ｒＣＢＦ显著降低（ｔ＝２１２～２５４，Ｐ＜００５）；与ＬＡ（－）组相比，额叶和顶叶皮质、ＬＡ区域ｒＣＢＦ显著减少（ｔ＝２１１～２６０，Ｐ＜００５）；ＬＡ（＋）组长谷川智能评分与额叶皮质、ＬＡ区域ｒＣＢＦ变化呈显著正相关（ｒ＝０７６５，Ｐ＜００１和ｒ＝０４３９，Ｐ＜００５）。结果表明，伴ＬＡ的多发性脑梗塞病人，ＬＡ区和皮质区域存在广泛血流灌注不足，持续的低灌注状态可引起脑功能低下，并与痴呆的程度有一定关系；脑血流ＳＰＥＣＴ显像具有独特优势和价值。     

Optimal inversion time for acquiring flow-sensitive alternating inversion recovery images to quantify regional cerebral blood flow

The purpose of this study was to correlate regional cerebral blood flow (rCBF) measured by I-123-IMP and flow-sensitive alternating inversion recovery (FAIR) studies with different inversion time (TI) values to find out the optimum TI that gives comparable rCBF and images on FAIR study. Nine patients with symptoms and signs of internal carotid or major cerebral arterial stenosis were enrolled in this study. Both I-123-IMP single photon emission computed tomography (SPECT) and FAIR images were acquired in all patients. Single-slice FAIR images (with different TI values) were acquired using a 1.5-T MRI unit. The rCBF was calculated from all I-123-IMP and FAIR images. Receiver operating characteristics (ROC) analysis was performed to detect hypoperfused segments on FAIR images. The rCBF calculated from FAIR and I-123-IMP studies were compared and correlated with each other. The ROC analysis showed no significant differences among the readers or TI values, but a trend of higher sensitivity, specificity, and accuracy was observed with TI of 1400 ms. The rCBF values of FAIR and I-123-IMP studies significantly correlated with each other. The FAIR images with TI value of 1400 ms gave more comparable CBF. A TI value of 1400 ms might be optimum for 1.5-T MR strength to get high quality FAIR images and comparable CBF. Electronic Publication     

Quantitative measurement of regional cerebrovascular reactivity to acetazolamide using 123I-N-isopropyl-p-iodoamphetamine autoradiography with SPECT: validation study using H2 15O with PET.

A simplified technique using (123)I-N-isopropyl-p-iodoamphetamine ((123)I-IMP) autoradiography (ARG) with SPECT has been proposed recently for quantifying regional cerebral blood flow (rCBF). To validate the accuracy of (123)I-IMP-ARG for quantifying regional cerebrovascular reactivity (rCVR) to acetazolamide, we compared rCVR determined using (123)I-IMP-ARG with that determined using H(2)(15)O PET. METHODS: Thirty-nine patients with chronic stenoocclusive disease in a unilateral major cerebral artery underwent SPECT and PET studies before and after intravenous administration of acetazolamide. The rCBF images in the 4 conditions in each patient were calculated according to the ARG method. The same standard input function and the same distribution volume of 35 mL/mL were used in the calculation of rCBF images using the (123)I-IMP-ARG method at resting state and with acetazolamide challenge. One large cortical region of interest (ROI) for a unilateral middle cerebral artery territory was bilaterally determined on each standardized summed rCBF image. On the basis of the rCBF values in each ROI, rCVR to acetazolamide was calculated as follows: rCVR (%) = ([acetazolamide challenge rCBF - resting rCBF]/resting rCBF) x 100. RESULTS: Significant correlation was observed between rCVR values obtained using (123)I-IMP-ARG and H(2)(15)O PET methods in the 78 ROIs examined in the 39 patients (r = 0.820; P < 0.0001). When a rCVR lower than the mean - 2 SD of values obtained in healthy volunteers (18.4% for (123)I-IMP-ARG and 18.2% for H(2)(15)O PET) was defined as reduced, and when the H(2)(15)O PET method was assumed to represent the true determinant of rCVR, (123)I-IMP-ARG was 90% sensitive and 92% specific and displayed an 87% positive predictive value for detecting patients with reduced rCVR. CONCLUSION: These findings demonstrate that (123)I-IMP-ARG methods accurately quantify rCVR and can adequately define subgroups of patients with reduced rCVR.     

Poststenotic signal attenuation on 3 D phase-contrast MR angiography: a useful finding in haemodynamically significant carotid artery stenosis

We performed blinded visual evaluation of MR angiography (MRA) films in 44 patients with unilateral carotid artery stenosis to determine whether a flow gap and poststenotic signal attenuation on 3 D-PC MRA were useful signs of severe carotid artery stenosis. Although nine patients with a flow gap alone had various degrees of stenosis ranging from 22.2 to 77.3 % without any decrease in regional cerebral blood flow (rCBF), 13 patients with both a flow gap and poststenotic signal attenuation had severe stenoses of 80 % or more, with a definite decrease in baseline rCBF. The presence of both a flow gap and poststenotic signal attenuation on 3 D-PC MRA appeared to be a reliable marker of severe carotid artery stenosis with a decrease in rCBF. Received: 30 April 1999/Accepted: 11 August 2000     

Perfusion MRI in CNS disease: current concepts

Today there are several indications for cerebral perfusion MRI. The major indications routinely used in increasing numbers of imaging centers include cerebrovascular disease, tumor imaging and recently psychiatric disorders. Perfusion MRI is based on the injection of a gadolinium chelate and the rapid acquisition of images as the bolus of contrast agent passes through the blood vessels in the brain. The contrast agent causes a signal change; this signal change over time can be analysed to measure cerebral hemodynamics. The quality of brain perfusion studies is very dependent on the contrast agent used: a robust and strong signal decrease with a compact bolus is needed. MultiHance (gadobenate dimeglumine, Gd-BOPTA) is the first of a new class of paramagnetic MR contrast agents with a weak affinity for serum proteins. Due to the interaction of Gd-BOPTA with serum albumin, MultiHance presents with significantly higher T1- and T2-relaxivities enabling a sharper bolus profile. This article reviews the indications of perfusion MRI and the performance of MultiHance in MR perfusion of different diseases. Previous studies using perfusion MRI for a variety of purposes required the use of double dose of contrast agent to achieve a sufficiently large signal drop to enable the acquisition of a clear input function and the calculation of perfusion rCBV and rCBF maps of adequate quality. Recent studies with Multi-Hance suggest that only a single dose of this agent is needed to cause a signal drop of about 30% which is sufficient to allow the calculation of high quality rCBV and rCBF maps.     

Donepezil hydrochloride preserves regional cerebral blood flow in patients with Alzheimer's disease.

The aim of this SPECT study was to investigate the effects of donepezil on regional cerebral blood flow (rCBF) in patients with mild to moderate Alzheimer's disease (AD) using statistical parametric mapping. METHODS: rCBF was noninvasively measured using (99m)Tc-ethyl cysteinate dimer in 35 AD patients with a Mini-Mental State Examination score > 16 on initial evaluation. Baseline and follow-up SPECT studies with a mean interval of 12 mo were performed on these patients. We used the adjusted rCBF images in the relative flow distribution (normalization of global cerebral blood flow for each patient to 50 mL/100 g/min with proportional scaling) to compare these groups through statistical parametric mapping. RESULTS: In the follow-up study, the adjusted rCBF was significantly preserved in the right and left anterior cingulate gyri, right middle temporal gyrus, right inferior parietal lobules, and prefrontal cortex of donepezil-treated AD patients, compared with placebo-treated AD patients. CONCLUSION: Treatment with donepezil for 1 y appears to reduce the decline in rCBF, suggesting preservation of functional brain activity.     

Cerebral blood flow index: dynamic perfusion MRI delivers a simple and good predictor for the outcome of acute-stage ischemic lesion

OBJECTIVES: To evaluate the feasibility of utilizing cerebral blood flow (CBF) index images, calculated automatically and quickly from dynamic perfusion imaging (DPI), to identify acute cerebral ischemia. We attempted to investigate (1) whether the CBF index has a threshold for assessing tissue outcome, (2) whether CBF index images can predict the resulting infracted area, and if so, (3) whether the predictive capacity of the CBF index image is comparable to the regional CBF (rCBF) image delivered from singular value decomposition (SVD) deconvolution methods, which are regarded as most accurate in predicting the final infarct area. METHODS: Diffusion-weighted images (DWI) and DPI were obtained in 17 patients within 12 hours of stroke onset and follow-up magnetic resonance imaging (MRI). On 3 DPI-delivered images, namely relative regional cerebral blood volume (rrCBV), uncorrected mean transit time (MTTu) and CBF index images, univariate discriminant analysis was done to estimate cut-off values to discriminate between infarcted and noninfarcted areas. Subsequently, correlations between the initial lesion volume of 3 images together with rCBF images delivered with SVD methods and the final infarct volume on follow-up T2-weighted MRI taken at the 8th to 20th day were determined. RESULTS: Among the 3 images, only the CBF index image was able reveal the threshold of the ischemic region. Lesion volume of CBF index images against follow-up infarct volume had the highest correlation (r = 0.995) to a linear fit and the slope was closest to 1.0 (0.91) among the 3 and had identical accuracy to the regression coefficient of rCBF images. CONCLUSIONS: CBF index images can predict final infarct volume. Evaluating CBF index images together with DWI can guide the initial assessment in the acute stage of cerebral ischemia.     

Cerebrovascular enhancement in spoiled GRASS (SPGR) images: comparison with spin-echo technique.

The signals and artifacts in cerebral blood vessels were systematically studied using a new three-dimensional Fourier transform (3DFT) technique, spoiled gradient recalled acquisition in steady state (SPGR), with parameters optimized for T1-weighted brain imaging. Twenty consecutive patients referred for routine cranial MR imaging were prospectively studied before and after the intravenous administration of Gd-DTPA using both 3DFT SPGR and conventional 2DFT SE imaging. A significant difference between the two techniques was noted in regard to the appearance of cerebral blood vessels and the degree of vascular pulsation artifact. Precontrast SPGR images demonstrated high signal in all (100%) internal carotid arteries and in nearly all (85-95%) vertebral, basilar, and proximal posterior, middle, and anterior cerebral arteries. High signal was variably present (5-50%) in more distal arterial branches. High signal from venous structures was not seen except in the superior sagittal sinus, which was bright in 75% of cases. Postcontrast SPGR images reliably demonstrated uniform high signal in all (100%) major arterial branches, up to fourth-order branches in the middle cerebral artery, diminishing toward the vertex. All (100%) major deep and superficial venous structures were of uniformly high signal, diminishing slightly as they exited the skull base. Flow related artifacts were found to be significantly (p = 0.001) reduced in contrast enhanced SPGR compared to SE images. As implemented in this study, SPGR and SE images demonstrate significantly different patterns of vascular signal that must be recognized for the proper interpretation of MR images.     

Contrast-enhanced MR angiography of intracranial giant aneurysms

BACKGROUND AND PURPOSE: Intravoxel phase dispersion and flow saturation often prevent adequate depiction of intracranial giant aneurysms on 3D time-of-flight (3D-TOF) MR angiography (MRA). Additional diagnostic difficulties may arise from T1 contamination artifact of an associated blood clot. Our aim was to assess whether contrast-enhanced MRA could improve the evaluation of giant aneurysms and to compare two different types of contrast-enhanced MRA. METHODS: We studied 11 aneurysms in 10 patients (age range, 31-77 years) with giant aneurysms of the anterior (n = 9) and posterior (n = 2) cerebral circulation by comparing 3D-TOF, first-pass dynamic contrast-enhanced MRA, and steady-state contrast-enhanced 3D-TOF sequences. Additional comparison with digital subtraction angiography (DSA) was performed in eight aneurysms. RESULTS: In nine of 11 aneurysms, 3D-TOF did not adequately show the lumen and exiting vessels. Contrast-enhanced 3D-TOF and dynamic contrast-enhanced MRA showed the aneurysm sac and exiting vessels in all of these cases. Dynamic contrast-enhanced MRA showed a better intravascular contrast than did contrast-enhanced 3D-TOF, which led to better delineation of the aneurysms. T1 contamination artifact from intra- or extraluminal blood clot was evident on the 3D-TOF images in four cases. The artifact was less marked on the contrast-enhanced 3D-TOF image and was completely eliminated on the dynamic contrast-enhanced MRA image by subtraction of precontrast images. The diagnostic information provided by dynamic contrast-enhanced MRA was comparable to that provided by DSA. CONCLUSION: Precontrast 3D-TOF is inadequate for the assessment of giant cerebral aneurysms. Both contrast-enhanced 3D-TOF and dynamic contrast-enhanced MRA reliably show the aneurysm sac and connected vessels. Dynamic MRA provides a superior contrast between flow and background and eliminates T1 contamination artifact. It should therefore be considered as the MRA sequence of choice.     

Reduction of errors in ASL cerebral perfusion and arterial transit time maps using image de‐noising

In this work, the performance of image de‐noising techniques for reducing errors in arterial spin labeling cerebral blood flow and arterial transit time estimates is investigated. Simulations were used to show that the established arterial spin labeling cerebral blood flow quantification method exhibits the bias behavior common to nonlinear model estimates, and as a result, the reduction of random errors using image de‐noising can improve accuracy. To assess the effect on precision, multiple arterial spin labeling data sets acquired from the rat brain were processed using a variety of common de‐noising methods (Wiener filter, anisotropic diffusion filter, gaussian filter, wavelet decomposition, and independent component analyses). The various de‐noising schemes were also applied to human arterial spin labeling data to assess the possible extent of structure degradation due to excessive spatial smoothing. The animal experiments and simulated data show that noise reduction methods can suppress both random and systematic errors, improving both the precision and accuracy of cerebral blood flow measurements and the precision of transit time maps. A number of these methods (and particularly independent component analysis) were shown to achieve this aim without compromising image contrast. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.