Tracer Delay Research Articles

Simultaneous phase-contrast MRI and PET for noninvasive quantification of cerebral blood flow and reactivity in healthy subjects and patients with cerebrovascular disease.

H215 O-positron emission tomography (PET) is considered the reference standard for absolute cerebral blood flow (CBF). However, this technique requires an arterial input function measured through continuous sampling of arterial blood, which is invasive and has limitations with tracer delay and dispersion. To demonstrate a new noninvasive method to quantify absolute CBF with a PET/MRI hybrid scanner. This blood-free approach, called PC-PET, takes the spatial CBF distribution from a static H215 O-PET scan, and scales it to the whole-brain average CBF value measured by simultaneous phase-contrast MRI. Observational. Twelve healthy controls (HC) and 13 patients with Moyamoya disease (MM) as a model of chronic ischemic disease. 3T/2D cardiac-gated phase-contrast MRI and H215 O-PET. PC-PET CBF values from whole brain (WB), gray matter (GM), and white matter (WM) in HCs were compared with literature values since 2000. CBF and cerebrovascular reactivity (CVR), which is defined as the percent CBF change between baseline and post-acetazolamide (vasodilator) scans, were measured by PC-PET in MM patients and HCs within cortical regions corresponding to major vascular territories. Statistical Tests: Linear, mixed effects models were created to compare CBF and CVR, respectively, between patients and controls, and between different degrees of stenosis. The mean CBF values in WB, GM, and WM in HC were 42 ± 7 ml/100 g/min, 50 ± 7 ml/100 g/min, and 23 ± 3 ml/100 g/min, respectively, which agree well with literature values. Compared with normal regions (57 ± 23%), patients showed significantly decreased CVR in areas with mild/moderate stenosis (47 ± 17%, P = 0.011) and in severe/occluded areas (40 ± 16%, P = 0.016). Data Conclusion: PC-PET identifies differences in cerebrovascular reactivity between healthy controls and cerebrovascular patients. PC-PET is suitable for CBF measurement when arterial blood sampling is not accessible, and warrants comparison to fully quantitative H215 O-PET in future studies. 3 Technical Efficacy Stage: 2 J. Magn. Reson. Imaging 2019. J. Magn. Reson. Imaging 2020;51:183-194.

Hepatocholescintigraphy in diagnosis of functional state of biliodigestive anastomoses

Aim. To identify diagnostic value of hepatocholescintigraphy for evaluation of functional state of biliodigestive anastomoses (BDA).Material and methods. 99mTc-IDA hepatocholescintigraphy was applied in 52 patients to evaluate function of biliodigestive anastomoses.Results. Scintigraphic signs of “bowel-anastomosis” and/or “BDA-intrahepatic bile ducts” reflux were revealed in 14 (27%) cases. Obstruction of biliodigestive anastomosis occurred in 3 (5.7%) patients. Normal bile flow through BDA was observed in 10 (19.2%) patients, impaired passage – in 21 (40.3%) cases. Tracer delay in intrahepatic bile ducts was noted in 21 (25.0%) cases, signs of adhesive process near deferent bowel – in 3 (3.8%) cases.Conclusion. Hepatocholescintigraphy is highly effective method to assess biliary tract in patients after Roux-en-Y biliodigestive anastomoses formation.

Estimation of Ischemic Core Volume Using Computed Tomographic Perfusion.

Background and Purpose- Estimation of infarction based on computed tomographic perfusion (CTP) has been challenging, mainly because of noise associated with CTP data. The Bayesian method is a robust probabilistic method that minimizes effects of oscillation, tracer delay, and noise during residue function estimation compared with other deconvolution methods. This study compares CTP-estimated ischemic core volume calculated by the Bayesian method and by the commonly used block-circulant singular value deconvolution technique. Methods- Patients were included if they had (1) anterior circulation ischemic stroke, (2) baseline CTP, (3) successful recanalization defined by thrombolysis in cerebral infarction ≥IIb, and (4) minimum infarction volume of >5 mL on follow-up magnetic resonance imaging (MRI). CTP data were processed with circulant singular value deconvolution and Bayesian methods. Two established CTP methods for estimation of ischemic core volume were applied: cerebral blood flow (CBF) method (relative CBF, <30% within the region of delay >2 seconds) and cerebral blood volume method (<2 mL per 100 g within the region of relative mean transit time >145%). Final infarct volume was determined on MRI (fluid-attenuated inversion recovery images). CTP and MRI-derived ischemic core volumes were compared by univariate and Bland-Altman analysis. Results- Among 35 patients included, the mean/median (mL) difference for CTP-estimated ischemic core volume against MRI was -4/-7 for Bayesian CBF ( P=0.770), 20/12 for Bayesian cerebral blood volume ( P=0.041), 21/10 for circulant singular value deconvolution CBF ( P=0.006), and 35/18 for circulant singular value deconvolution cerebral blood volume ( P<0.001). Among all methods, Bayesian CBF provided the narrowest limits of agreement (-28 to 19 mL) in comparison with MRI. Conclusions- Despite existing variabilities between CTP postprocessing methods, Bayesian postprocessing increases accuracy and limits variability in CTP estimation of ischemic core.

Fast nonlinear regression method for CT brain perfusion analysis

Although computed tomography (CT) perfusion (CTP) imaging enables rapid diagnosis and prognosis of ischemic stroke, current CTP analysis methods have several shortcomings. We propose a fast nonlinear regression method with a box-shaped model (boxNLR) that has important advantages over the current state-of-the-art method, block-circulant singular value decomposition (bSVD). These advantages include improved robustness to attenuation curve truncation, extensibility, and unified estimation of perfusion parameters. The method is compared with bSVD and with a commercial SVD-based method. The three methods were quantitatively evaluated by means of a digital perfusion phantom, described by Kudo etal. and qualitatively with the aid of 50 clinical CTP scans. All three methods yielded high Pearson correlation coefficients ([Formula: see text]) with the ground truth in the phantom. The boxNLR perfusion maps of the clinical scans showed higher correlation with bSVD than the perfusion maps from the commercial method. Furthermore, it was shown that boxNLR estimates are robust to noise, truncation, and tracer delay. The proposed method provides a fast and reliable way of estimating perfusion parameters from CTP scans. This suggests it could be a viable alternative to current commercial and academic methods.

Automated CT Perfusion for Ischemic Core Volume Prediction in Tandem Anterior Circulation Occlusions

Background/Aim: CT perfusion (CTP) predicts ischemic core volumes in acute ischemic stroke (AIS); however, assumptions made within the pharmacokinetic model may engender errors by the presence of tracer delay or dispersion. We aimed to evaluate the impact of hemodynamic disturbance due to extracranial anterior circulation occlusions upon the accuracy of ischemic core volume estimation with an automated perfusion analysis tool (RAPID) among AIS patients with large-vessel occlusions. Methods: A prospectively collected, interventional database was retrospectively reviewed for all cases of endovascular treatment of AIS between September 2010 and March 2015 for patients with anterior circulation occlusions with baseline CTP and full reperfusion (mTICI3). Results: Out of 685 treated patients, 114 fit the inclusion criteria. Comparison between tandem (n = 21) and nontandem groups (n = 93) revealed similar baseline ischemic core (20 ± 19 vs. 19 ± 25 cm³; p = 0.8), T_max >6 s (175 ± 109 vs. 162 ± 118 cm³; p = 0.6), T_max >10 s (90 ± 84 vs. 90 ± 91 cm³; p = 0.9), and final infarct volumes (45 ± 47 vs. 37 ± 45 cm³; p = 0.5). Baseline core volumes were found to correlate with final infarct volumes for the tandem (r = 0.49; p = 0.02) and nontandem (r = 0.44; p < 0.01) groups. The mean absolute difference between estimated core and final infarct volume was similar between patients with and those without (24 ± 41 vs. 17 ± 41 cm³; p = 0.5) tandem lesions. Conclusions: The prediction of baseline ischemic core volumes through an optimized CTP analysis employing rigorous normalization, thresholding, and voxel-wise analysis is not significantly influenced by the presence of underlying extracranial carotid steno-occlusive disease in large-vessel AIS.

Abstract WP6: RAPID Automated CT Perfusion Software Performance in Acute Ischemic Stroke From Anterior Circulation Tandem Occlusions

Purpose: CT perfusion predicts ischemic core volumes in acute stroke (AIS), however assumptions within the pharmacokinetic model may engender errors in the presence of tracer delay or dispersion. We aim to evaluate the impact of hemodynamic disturbance due to tandem intracranial-extracranial anterior circulation occlusions upon the accuracy of the ischemic core estimation in an automated perfusion analysis tool (RAPID) among large-vessel AIS patients. Materials and Methods: A prospectively collected interventional database was retrospectively reviewed for all cases of endovascular treatment of AIS between September 2010-March 2015 for patients with anterior circulation occlusions with baseline CTP and full reperfusion (mTICI3). This study was IRB approved. Results: Out of 685 treated patients, 114 fit the inclusion criteria. The comparison between tandem (n=21) vs. non-tandem groups (n=93) revealed similar baseline ischemic core (20±19vs.19±25cc; p=0.8), Tmax&gt;6s (175±109vs.162±118cc; p=0.6), Tmax&gt;10s (90±84vs.90±91cc; p=0.9) and final infarct volumes (45±47vs.37±45cc; p=0.5), respectively. Baseline core volumes were found to correlate with final infarct volumes for the tandem (r=0.49; p=0.02) and non-tandem (r=0.44; p=&lt;0.01) groups. The mean absolute difference between estimated core and final infarct volume was similar between patients with and without (24±41vs.17±41cc; p=0.5) tandem lesions. Conclusions: Optimized CTP analysis employing rigorous normalization, thresholding, and voxel-wise analysis is reliable for ischemic core prediction in AIS patients despite underlying extracranial carotid steno-occlusive disease.

Hemodynamic Parameter Estimation From Magnetic Resonance Perfusion Imaging With the Tikhonov Regularization Method

In the brain, T2-weighted dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) enables the measurements of hemodynamic parameters, such as cerebral blood flow (CBF) and cerebral blood volume. Accurately characterizing the tissue residue function in DSC-MRI is of crucial importance to the quantification of cerebral hemodynamics. The estimation of the tissue residue function is an inverse problem, and one of the approaches is through the deconvolution. In this paper, Tikhonov regularization is used to reconstruct the residue function with smooth constraints. The influences of pertinent factors, such as signal-to-noise ratio (SNR) and tracer delay on the reconstruction, are analyzed in detail. The simulation results show that the SNR and the tracer delay have little influence on the estimation of CBF. Therefore, the Tikhonov regularization method can accurately estimate the CBF with confidence.

Assessment of the Tracer Delay Effect in Whole-Brain Computed Tomography Perfusion

Whole-brain computed tomography perfusion (CTP) data sets generated by tracer delay-insensitive singular value decomposition plus (SVD+) and standard singular value decomposition (sSVD) deconvolution algorithms were evaluated to quantify relatedness and discrepancies in CTP results. Twenty females with symmetrical hemispheric CTP maps indicative of brain tissue without apparent abnormalities were studied. Tissue-specific CTP values were analyzed. Standard SVD values were higher than SVD+ for cerebral blood flow. Other CTP values had minimal differences across brain regions. All simple linear regression models were statistically significant (P < 0.05) except for cerebral blood flow in white matter (P = 0.06). Cerebral blood volume had a good model fit, and mean transit time, a poor fit. Corresponding fitted CTP values for sSVD and SVD+ based on regression equations for brain-tissue types are presented. Additional research is required to compare SVD+ and sSVD in disease states when significant hemodynamic brain alterations are present.

Assessment of Tracer Delay Effect in Whole-Brain Computed Tomography Perfusion

The objective of this study was to compare the variability of computed tomography perfusion (CTP) results in identical data sets of middle cerebral artery (MCA) acute ischemic stroke (AIS) generated by standard singular value decomposition (sSVD) deconvolution and tracer delay-insensitive singular value decomposition (SVD+) algorithm analyses. Whole-brain 320-detector-row CTP data sets from 9 unilateral MCA AIS cases and 9 controls were retrospectively analyzed. Computed tomography perfusion values for the combined core/penumbra, contralateral hemispheres and arterial territories were measured and compared with literature values. Simple linear regression models are provided to predict corresponding SVD+ value and sSVD CTP values. In the core/penumbra, sSVD generated lower cerebral blood flow (CBF) values, higher mean transit time (MTT) values, and a broader range of CBF and MTT values as compared with SVD+. Mean transit time value differences between the core/penumbra and contralateral hemispheres were statistically significant using sSVD, whereas those of SVD+ were not. Goodness of fit between algorithms for the core/penumbra was lower for CBF (0.483) and MTT (0.494), as compared with time to peak (0.891) and cerebral blood volume (0.997). In this study using identical source data for patients with MCA AIS, use of either sSVD or SVD+ analyses created statistically significant differences in the CTP value results. Tracer delay-sensitive and -insensitive algorithms impact CTP results in AIS and controls, highlighting the need to pursue additional studies that assess the variability, accuracy, and clinical implications of CTP results generated when using heterogeneous deconvolution algorithms.

The Application of Magnetic Resonance Perfusion Imaging in the Estimation of Brain Function Using SVD Method

MR perfusion imaging can be used to estimate parameters indicating the metabolic process, including cerebral blood flow (CBF). Specifically singular value decomposition (SVD) method is applied in this paper to obtain CBF with a predefined conventional arterial input function (AIF), and the effects of threshold and tracer delay are investigated. While the simulation results show that SVD method can estimate CBF with good accuracy by using different thresholds for different flow values, the method is found to be sensitive to tracer delay. A delay correction scheme is advocated, where CBF is determined by SVD after time-shifting of the tracer concentration curve. With the correction the simulation results are considerably improved in the flow estimation.

Correction

HomeStrokeVol. 43, No. 5Correction Free AccessCorrectionPDF/EPUBAboutView PDFView EPUBSections ToolsAdd to favoritesDownload citationsTrack citationsPermissions ShareShare onFacebookTwitterLinked InMendeleyReddit Jump toFree AccessCorrectionPDF/EPUBCorrection Originally published1 May 2012https://doi.org/10.1161/STR.0b013e3182574d16Stroke. 2012;43:e54This article corrects the followingGrading Carotid Stenosis Using Ultrasonic MethodsThe article entitled, “Grading Carotid Stenosis Using Ultrasonic Methods,” by von Reutern et al, which published in the March 2012 issue of the journal (Stroke. 2012;43:916–921), included an error in the running head of the article (on pages 917, 919, and 921). The running head should be: “Grading Carotid Stenosis” Also, in the author's list Dr von Reutern's name appeared twice. Dr von Reutern is the first author. These errors have been corrected in the online version of the article and Table of Contents. Previous Back to top Next FiguresReferencesRelatedDetailsCited By Hanson E, Roach C, Day K, Ghosh K, Peters K, Bradley W and Orrison W (2013) Assessment of Tracer Delay Effect in Whole-Brain Computed Tomography Perfusion, Journal of Computer Assisted Tomography, 10.1097/RCT.0b013e318280a465, 37:2, (222-232), . Hanson E, Roach C, Day K, Peters K, Bradley W, Ghosh K, Patton P, McMurray R and Orrison W (2013) Assessment of the Tracer Delay Effect in Whole-Brain Computed Tomography Perfusion, Journal of Computer Assisted Tomography, 10.1097/RCT.0b013e31828004bb, 37:2, (212-221), . Related articlesGrading Carotid Stenosis Using Ultrasonic MethodsGerhard-Michael von Reutern, et al. Stroke. 2012;43:916-921 May 2012Vol 43, Issue 5 Advertisement Article InformationMetrics © 2012 American Heart Association, Inc.https://doi.org/10.1161/STR.0b013e3182574d16 Originally publishedMay 1, 2012 PDF download Advertisement

Susceptibility of Tmax to Tracer Delay on Perfusion Analysis: Quantitative Evaluation of Various Deconvolution Algorithms Using Digital Phantoms

The time-to-maximum of the tissue residue function (T(max)) perfusion index has proven very predictive of infarct growth in large clinical trials, yet its dependency on simple tracer delays remains unknown. Here, we determine the dependency of computed tomography (CT) perfusion (CTP) T(max) estimates on tracer delay using a range of deconvolution techniques and digital phantoms. Digital phantom data sets simulating the tracer delay were created from CTP data of six healthy individuals, in which time frames of the left cerebral hemisphere were shifted forward and backward by up to ±5 seconds. These phantoms were postprocessed with three common singular value decomposition (SVD) deconvolution algorithms-standard SVD (sSVD), block-circulant SVD (bSVD), and delay-corrected SVD (dSVD)-with an arterial input function (AIF) obtained from the right middle cerebral artery (MCA). The T(max) values of the left hemisphere were compared among different tracer delays and algorithms by a region of interest-based analysis. The T(max) values by sSVD were positively correlated with 'positive shifts' but unchanged with 'negative shifts,' those by bSVD had an excellent positive linear correlation with both positive and negative shifts, and those by dSVD were relatively constant, although slightly increased with the positive shifts. The T(max) is a parameter highly dependent on tracer delays and deconvolution algorithm.

Difference in Tracer Delay–induced Effect among Deconvolution Algorithms in CT Perfusion Analysis: Quantitative Evaluation with Digital Phantoms

Institutional review board approval and informed consent were obtained. The purpose was to evaluate the differences in tracer delay-induced effects of various deconvolution algorithms for computed tomographic (CT) perfusion imaging by using digital phantoms created from actual source data. Three methods of singular value decomposition (SVD) were evaluated. For standard SVD (sSVD), the delays induced significant errors in cerebral blood flow and mean transit time. In contrast, for block-circulant SVD (bSVD), these values remained virtually unchanged, whereas for delay-corrected SVD (dSVD), mild changes were observed. bSVD was superior to sSVD and dSVD for avoiding the tracer delay-induced effects in CT perfusion imaging.

Tracer Delay–Insensitive Algorithm Can Improve Reliability of CT Perfusion Imaging for Cerebrovascular Steno-Occlusive Disease: Comparison with Quantitative Single-Photon Emission CT

Reliability of CT perfusion (CTP) algorithms has not been fully validated. We investigated whether the cerebral blood flow (CBF) values obtained by using a dynamic CTP technique with a tracer delay-insensitive deconvolution algorithm are more accurate than those obtained by using CTP with delay-sensitive algorithms in unilateral cerebrovascular steno-occlusive disease, when compared with those generated by quantitative single-photon emission CT (SPECT). Using CTP and iodine-123-N-isopropyl-p-iodoamphetamine SPECT with an autoradiographic quantification technique, we examined 20 patients with suggested hemodynamic ischemia due to stenosis or occlusion of the unilateral internal carotid or middle cerebral artery. The algorithms used for CTP included delay-insensitive block-circulant singular value decomposition (SVD) (bSVD) and delay-sensitive standard SVD (sSVD) and box-modulation transfer function (bMTF). Absolute CBF values obtained by using CTP with bSVD were significantly lower than those obtained with SPECT, but the ratios to the nonaffected side were significantly correlated to the quantitative SPECT values with significant agreements, particularly when the arterial input function was obtained from the unaffected side. Contrastingly, CBF ratios with sSVD and bMTF were significantly underestimated, and no significant agreement was determined between CTP with sSVD or bMTF and SPECT, though there were substantial correlations between them in some parameters. With the CTP technique, the insensitivity of the deconvolution algorithm to the tracer-delay effect appears to be essential for estimating semiquantitative CBF values in patients with unilateral steno-occlusive lesions.

Hyperacute stroke patients and catheter thrombolysis therapy: correlation between computed tomography perfusion maps and final infarction

We investigated the correlation between abnormal perfusion areas by computed tomography perfusion (CTP) study of hyperacute stroke patients and the final infarction areas after intraarterial catheter thrombolysis. CTP study using the box-modulation transfer function (box-MTF) method based on the deconvolution analysis method was performed in 22 hyperacute stroke patients. Ischemic lesions were immediately treated with catheter thrombolysis after CTP study. Among them, nine patients with middle cerebral artery (MCA) occlusion were investigated regarding correlations of the size of the prolonged mean transit time (MTT) area, the decreased cerebral blood volume (CBV) area, and the final infarction area. Using the box-MTF method, the prolonged MTT area was almost identical to the final infarction area in the case of catheter thrombolysis failure. The decreased CBV areas resulted in infarction or hemorrhage, irrespective of the outcome of recanalization after catheter thrombolysis. The prolonged MTT areas, detected by the box-MTF method of CTP in hyperacute stroke patients, included the area of true prolonged MTT and the tracer delay. The prolonged MTT area was almost identical to the final infarction area when recanalization failed. We believe that a tracer delay area also indicates infarction in cases of thrombolysis failure.

Sestamibi Scans Are Not All Created Equally

The sensitivity of sestamibi scanning techniques used for preoperative localization in primary hyperparathyroidism is a function of the parameters of image acquisition and processing. Criterion standard vs optimized technique. Tertiary referral center. One hundred forty-eight consecutive patients with primary hyperthyroidism were analyzed. Under the initial protocol, 97 patients underwent a preexisting standard sestamibi--single-photon emission computed tomographic scan and surgical exploration. The scanning technique was modified and in the revised protocol, 51 patients underwent imaging and surgical exploration. Image acquisition and processing revisions as follows: patient positioning standardized, collimator resolution adjusted, radioactive tracer delay extended, visualization field broadened, data extraction refined, and image processing filter modified. concordance among the scan and operative localization, lateralization, and cure rate. Initial protocol: 97 patients underwent surgery for primary hyperthyroidism with the initial sestamibi design. Eighty-one patients (83%) had a positive result, that is, at least 1 gland was identified; 77 patients (79%) had correct lateralization; and 49 patients (52%) had precise localization. Revised protocol: 51 patients underwent imaging under the optimized protocol. Forty-nine patients (96) had a positive result; 47 patients (92%) had correct lateralization; and 36 patients (70%) had precise localization. These improvements were significant, with P<.05 for localization and P<.01 for lateralization. Cure rates were 96% in both groups, confirmed by laboratory and pathologic findings. Sestamibi optimization in primary hyperparathyroidism can improve scan sensitivity. This may permit a focused minimally invasive operation.

Tracer Delay Correction of Cerebral Blood Flow with Dynamic Susceptibility Contrast-Enhanced MRI

Cerebral blood flow (CBF) and vascular mean transit time (MTT) can be determined by dynamic susceptibility contrast-enhanced magnetic resonance imaging and deconvolution with an arterial input function. However, deconvolution by a singular value decomposition (SVD) method is sensitive to the tracer delay that often occurs in patients with cerebrovascular disease. We investigated the effect of tracer delay on CBF determined by SVD deconvolution. Simulation study showed that underestimation of CBF due to tracer delay was larger for shorter MTTs. We developed a delay correction method that determines tracer delay by means of least-squares fitting pixel-by-pixel. The corrected CBF was determined by SVD deconvolution after time-shifting of the measured concentration curve. The simulations showed that the corrected CBF was insensitive to tracer delay irrespective of the vascular model, although CBF fluctuation increased slightly. We applied the delay correction to the CBF and MTT images acquired for nine patients with hyperacute stroke and unilateral occlusion of the middle cerebral artery. We found in some patients that the delay correction modulated the contrast of CBF and MTT images. For hyperacute stroke patients, tracer delay correction is essential to obtain reliable perfusion image when SVD deconvolution is used.

Effect of Regional Tracer Delay on CBF in Healthy Subjects Measured with Dynamic Susceptibility Contrast-Enhanced MRI: Comparison with 15O-PET

Deconvolution based on truncated singular value decomposition (SVD deconvolution) is a promising method for measuring cerebral blood flow (CBF) with dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI), but it has proved extremely sensitive to tracer delay. The purpose of this study was to investigate the effect of regional tracer delay on CBF determined by SVD deconvolution (SVD-CBF). SVD-CBFs with and without correction for the delay were compared with CBF measured by positron emission tomography (PET-CBF), which is regarded as the gold standard for quantification of CBF. Perfusion MRI and PET were performed on seven healthy men. In the PET study, the CBF image was obtained with bolus injection of H2(15)O and continuous arterial sampling. In the DSC-MRI study with bolus injection of Gd-based contrast agent, dynamic perfusion data were obtained with a 1.5T scanner at 1-s intervals by means of gradient-echo echo-planar imaging. CBF was determined by the SVD deconvolution method with and without correction for the tracer delay. Region-of-interest measurements were obtained in the gray matter (cerebral cortex in the middle cerebral artery territory) and white matter (centrum semiovale). Tracer delay was significantly longer in white matter than in gray matter (1.45+/-0.61 s vs. 0.59+/-0.35 s, P<0.01). Correction for the delay increased SVD-CBF in the white matter and consequently reduced the gray-to-white SVD-CBF ratio. The uncorrected gray-to-white SVD-CBF ratio was significantly larger than that of PET-CBF (3.33+/-0.66 vs. 2.54+/-0.49, P<0.01). However, the gray-to-white delay-corrected SVD-CBF ratio did not differ significantly from that of PET-CBF (2.83+/-0.31 vs. 2.54+/-0.49, P=0.10). The tracer delay in DSC-MRI causes errors in CBF estimates, even in healthy persons, and therefore should be corrected for when delay-sensitive deconvolution, such as SVD deconvolution, is used.

Measurement of cerebral circulation by dynamic susceptibility contrast-enhanced MRI: effect of tracer delay

Abstract Cerebral blood flow (CBF) and mean transit time (MTT) can be determined by dynamic susceptibility contrast-enhanced magnetic resonance imaging (DSC-MRI) and deconvolution with an arterial input function (AIF). However, deconvolution with a singular value decomposition (SVD) method is sensitive to the tracer delay that often occurs in patients with cerebrovascular disease. We developed a delay correction method that determines tracer delay by means of least-squares fitting pixel-by-pixel. The corrected CBF was determined by SVD deconvolution after time-shifting of the measured concentration curve. The simulations showed that the corrected CBF was insensitive to tracer delay irrespective of the vascular model, although CBF fluctuation increased slightly. We applied the delay correction to the CBF and MTT images acquired for a patient with hyperacute stroke and unilateral occlusion of the middle cerebral artery. The delay correction modulated the contrast of perfusion images. For hyperacute stroke patients, tracer delay correction is essential to obtain reliable CBF and MTT images when SVD deconvolution is used.

急性期脳病態の最新画像診断 画像による治療可能域の検出と問題点

Functional imaging including perfusion study has been feasible in acute cerebral ischemia, which can provide the information of areas of pneumbra or tissue at risk even by MR examination. Pathophysiological significance or clinical usefulness of perfusion-diffusion MRI, however, has not been confirmed because of lack of comparison with experimental inspection or investigation of prediction for risk of thrombolysis. Some methodological drawbacks, i.e., tracer delay effect on dynamic susceptibility-contrast MRI, cause serious underestimation of CBF value in evaluating remediable area on perfusion MRI. Oxygen metabolic imaging by PET would be superior to MRI in detecting areas of evolving infarct in the hyperacute stage of cerebral infarction. Considering these unsolved problems, development of proper correction to improve accuracy of the method with the validation of physiological phenomenon would be needed in the functional MR imaging in the clinical state of the hyperacute stage of cerebral infarction.