Quantitative Perfusion Values Research Articles

Recommendations for quantitative cerebral perfusion MRI using multi-timepoint arterial spin labeling: Acquisition, quantification, and clinical applications.

Accurate assessment of cerebral perfusion is vital for understanding the hemodynamic processes involved in various neurological disorders and guiding clinical decision-making. This guidelines article provides a comprehensive overview of quantitative perfusion imaging of the brain using multi-timepoint arterial spin labeling (ASL), along with recommendations for its acquisition and quantification. A major benefit of acquiring ASL data with multiple label durations and/or post-labeling delays (PLDs) is being able to account for the effect of variable arterial transit time (ATT) on quantitative perfusion values and additionally visualize the spatial pattern of ATT itself, providing valuable clinical insights. Although multi-timepoint data can be acquired in the same scan time as single-PLD data with comparable perfusion measurement precision, its acquisition and postprocessing presents challenges beyond single-PLD ASL, impeding widespread adoption. Building upon the 2015 ASL consensus article, this work highlights the protocol distinctions specific to multi-timepoint ASL and provides robust recommendations for acquiring high-quality data. Additionally, we propose an extended quantification model based on the 2015 consensus model and discuss relevant postprocessing options to enhance the analysis of multi-timepoint ASL data. Furthermore, we review the potential clinical applications where multi-timepoint ASL is expected to offer significant benefits. This article is part of a series published by the International Society for Magnetic Resonance in Medicine (ISMRM) Perfusion Study Group, aiming to guide and inspire the advancement and utilization of ASL beyond the scope of the 2015 consensus article.

Abstract 16817: Comparison of Diagnostic Performance of Quantitative Perfusion Stress Myocardial Perfusion Imaging With Cardiac Magnetic Resonance Between Different Vasodilators

Introduction: Adenosine and regadenoson are commonly used vasodilators in myocardial perfusion imaging for assessment of suspected coronary artery disease. Hypothesis: The aim of this study is to determine the difference between the different vasodilators by quantifying stress and rest myocardial perfusion using cardiovascular magnetic resonance (CMR). Methods: Subjects with known or suspected CAD from 10 centers undergoing invasive coronary angiography or CT angiography were enrolled for rest and stress first-pass perfusion images using dual sequence. First-pass stress perfusion images were acquired on 1.5T or 3.0T GE scanner during adenosine or Regadenoson. Fully quantitative perfusion values were determined using Fermi deconvolution. Significant CAD was defined by: presence of≥50% stenosis in the left main coronary artery or ≥70% in the one major vessel. Diagnostic performance of stress myocardial blood flow (MBF) and myocardial perfusion reserve (MPR) was measured using receiver operating characteristics curves. Results: A total of 89 subjects were recruited with a median age of 66 yrs, 69% men, 55% significant CAD, history of hypertension in 78%, diabetes in 48%, and hyperlipidemia in 74%. 36 subjects used adenosine, while 53 used regadenoson as the vasodilator agent. Stress MBF had a good area under the curve for adenosine vs. regadenoson [ 0.89 (0.78-1.00) vs. 0.82 (0.66-0.98), p=0.43], sensitivity (100% vs. 84%), and specificity (80% vs. 80%). MPR had a higher area under the curve for adenosine than regadenoson [0.87 (0.75-0.98) vs. 0.68 (0.52-0.84), p=0.06], sensitivity (100% vs. 61%), and specificity (68% vs. 73%). (Figure) Conclusions: Our study showed that fully quantitative perfusion using CMR, regadenoson, and adenosine have similar good diagnostic accuracy when stress MBF was used as the diagnostic parameter. However, adenosine outperformed regadenoson for the detection of significant CAD when MPR was used as the diagnostic parameter.

Quantitative myocardial perfusion with a hybrid 2D simultaneous multi-slice sequence

PurposeTo evaluate a novel 2D simultaneous multi-slice (SMS) myocardial perfusion acquisition and compare directly to a published quantitative 3D stack-of-stars (SoS) acquisition. MethodsA hybrid saturation recovery radial 2D SMS sequence following a single saturation was created for the quantification of myocardial blood flow (MBF). This sequence acquired three slices simultaneously and generated an arterial input function (AIF) using the first 24 rays. Validation was done in a novel way by alternating heartbeats between the hybrid 2D SMS and the 3D SoS acquisitions. Initial studies were done to study the effects of using only every other beat for the 2D SMS in two subjects, and for the 3D SoS in four subjects. The proposed alternating acquisitions were then performed in ten dog studies at rest, four dog studies at adenosine stress, and two human resting studies. Quantitative MBF analysis was performed for 2D SMS and 3D SoS separately, using a compartment model. ResultsAcquiring every-other-beat data resulted in 6 ± 5% (“ideal”) and 11 ± 8% (“practical”) perfusion changes for both 2D SMS and 3D SoS methods. For alternating acquisitions, 2D SMS and 3D SoS quantitative perfusion values were comparable for both the twelve rest studies (2D SMS: 0.69 ± 0.16 vs 3D: 0.69 ± 0.15 ml/g/min, p = 0.55) and the four stress studies (2D SMS: 1.28 ± 0.22 vs 3D: 1.30 ± 0.24 ml/g/min, p = 0.61). ConclusionEvery-other-beat acquisition changed estimated perfusion values relatively little for both sequences. The quantitative hybrid radial 2D SMS myocardial first-pass perfusion imaging sequence gave results similar to 3D perfusion when compared directly with an alternating beat acquisition.

Iterative reconstruction algorithm improves the image quality without affecting quantitative measurements of computed tomography perfusion in the upper abdomen

ObjectiveTo investigate differences between reconstruction algorithms in quantitative perfusion values and time-attenuation curves in computed tomography perfusion (CTP) examinations of the upper abdomen. MethodsTwenty-six CTP examinations were reconstructed with filtered back projection and an iterative reconstruction algorithm, advanced modeled iterative reconstruction (ADMIRE), with different levels of noise-reduction strength. Using the maximum-slope model, quantitative measurements were obtained: blood flow (mL/min/100 mL), blood volume (mL/100 mL), time to peak (s), arterial liver perfusion (mL/100 mL/min), portal venous liver perfusion (mL/100 mL/min), hepatic perfusion index (%), temporal maximum intensity projection (Hounsfield units (HU)) and temporal average HU. Time-attenuation curves for seven sites (left liver lobe, right liver lobe, hepatocellular carcinoma, spleen, gastric wall, pancreas, portal vein) were obtained. Mixed-model analysis was used for statistical evaluation. Image noise and the signal:noise ratio (SNR) were compared between four reconstructions, and statistical analysis of these reconstructions was made with a related-samples Friedman’s two-way analysis of variance by ranks test. ResultsThere were no significant differences for quantitative measurements between the four reconstructions for all tissues. There were no significant differences between the AUC values of the time-attenuation curves between the four reconstructions for all tissues, including three automatic measurements (portal vein, aorta, spleen). There was a significant difference in image noise and SNR between the four reconstructions. ConclusionsADMIRE did not affect the quantitative measurements or time-attenuation curves of tissues in the upper abdomen. The image noise was lower, and the SNR higher, for iterative reconstructions with higher noise-reduction strengths.

Validation of Automated Perfusion-Weighted Phase-Resolved Functional Lung (PREFUL)-MRI in Patients With Pulmonary Diseases.

Perfusion-weighted (Qw) noncontrast-enhanced proton lung MRI is a promising technique for assessment of pulmonary perfusion, but still requires validation. To improve perfusion-weighted phase-resolved functional lung (PREFUL)-MRI, to validate PREFUL with perfusion single photon emission computed tomography (SPECT) as a gold standard, and to compare PREFUL with dynamic contrast-enhanced (DCE)-MRI as a reference. Retrospective. Twenty patients with chronic obstructive pulmonary disease (COPD), 14 patients with cystic fibrosis (CF), and 21 patients with chronic thromboembolic pulmonary hypertension (CTEPH) were included. For PREFUL-MRI, a spoiled gradient echo sequence and for DCE-MRI a 3D time-resolved angiography with stochastic trajectories sequence were used at 1.5T. PREFUL-MRI coronal slices were acquired in free-breathing. DCE-MRI was performed in breath-hold with injection of 0.03 mmol/kg bodyweight of gadoteric acid at a rate of 4 cc/s. Perfusion SPECT images were obtained for six CTEPH patients. Images were coregistered. An algorithm to define the appropriate PREFUL perfusion phase was developed using perfusion SPECT data. Perfusion defect percentages (QDP) and Qw-values were calculated for all methods. For PREFUL quantitative perfusion values (PREFULQ ) and for DCE pulmonary blood flow (PBF) was calculated. Obtained parameters were assessed using Pearson correlation and Bland-Altman analysis. Qw-SPECT correlated with Qw-DCE (r = 0.50, P < 0.01) and Qw-PREFUL (r = 0.47, P < 0.01). Spatial overlap of QDP maps showed an agreement ≥67.7% comparing SPECT and DCE, ≥64.1% for SPECT and PREFUL, and ≥60.2% comparing DCE and PREFUL. Significant correlations of Qw-PREFUL and Qw-DCE were found (COPD: r = 0.79, P < 0.01; CF: r = 0.77, P < 0.01; CTEPH: r = 0.73, P < 0.01). PREFULQ /PBF correlations were similar/lower (CF, CTEPH: P > 0.12; COPD: P < 0.01) compared to Qw-PREFUL/DCE correlations. PREFULQ -values were higher/similar compared to PBF-values (COPD, CF: P < 0.01; CTEPH: P = 0.026). The automated PREFUL algorithm may allow for noncontrast-enhanced pulmonary perfusion assessment in COPD, CF, and CTEPH patients comparable to DCE-MRI. Level of Evidence 3 Technical Efficacy Stage 2 J. Magn. Reson. Imaging 2020;52:103-114.

Robust pCASL perfusion imaging using a 3D Cartesian acquisition with spiral profile reordering (CASPR).

To improve the robustness of arterial spin-labeled measured perfusion using a novel Cartesian acquisition with spiral profile reordering (CASPR) 3D turbo spin echo (TSE) in the brain and kidneys. The CASPR view ordering followed a pseudo-spiral trajectory on a Cartesian grid, by sampling the center of k-space at the beginning of each echo train of a segmented 3D TSE acquisition. With institutional review board approval and written informed consent, 14 normal subjects (9 brain and 5 kidneys) were scanned with pCASL perfusion imaging using 3D CASPR and compared against 3D linear TSE (brain and kidneys), the established 2D EPI and 3D gradient and spin echo perfusion (brain), and 2D single-shot turbo spin-echo perfusion (kidneys). The SNR and the quantitative perfusion values were compared among different acquisitions. 3D CASPR TSE achieved robust perfusion across all slices compared to 3D linear TSE in the brain and kidneys. Compared to 2D EPI, 3D CASPR TSE showed higher SNR across the brain (P < 0.01), and exhibited good agreement (36.4 ± 4.7 and 36.9 ± 5.3 mL/100 g/min with 2D EPI and 3D CASPR, respectively), and with 3D gradient and spin echo (27.9 ± 7.2 mL/100 g/min). Compared to a single slice 2D single-shot turbo spin-echo acquisition, 3D CASPR TSE achieved robust perfusion across the entire kidneys in similar scan time with comparable quantified perfusion values (154.1 ± 74.6 and 151.7 ± 70.6 mL/100 g/min with 2D single-shot turbo spin-echo and 3D CASPR, respectively). The CASPR view ordering with 3D TSE achieves robust arterial spin-labeled perfusion in the brain and kidneys because of the sampling of the center of k-space at the beginning of each echo train.

The Efficacy of Cone-Beam CT–Based Liver Perfusion Mapping to Predict Initial Response of Hepatocellular Carcinoma to Transarterial Chemoembolization

PurposeTo evaluate efficacy of cone-beam CT–based liver perfusion mapping obtained immediately following conventional transarterial chemoembolization of hepatocellular carcinoma (HCC) for assessing tumor vascularity, technical success of chemoembolization, and treatment response. Materials and MethodsFrom July 2015 to June 2016, 35 patients with 57 HCCs who underwent cone-beam CT with post-processing software via conventional transarterial chemoembolization for HCC and follow-up examination were included. Three reviewers evaluated technical success on angiography, unenhanced cone-beam CT, contrast-enhanced cone-beam CT, and cone-beam CT–based liver perfusion mapping after transarterial chemoembolization per tumor and per patient. Parenchymal blood volume (PBV) was measured. Treatment response was determined on follow-up CT, MR imaging, or histopathology according to modified Response Evaluation Criteria In Solid Tumors. Diagnostic performance for detection of a viable tumor was evaluated using multiple logistic regression with C-statistics. ResultsTreatment response was 38, 17, 2, and 0 for complete response, partial response, stable disease, and progressive disease per tumor and 18, 15, 2, and 0 per patient. In multiple logistic regression, unenhanced cone-beam CT, contrast-enhanced cone-beam CT, cone-beam CT–based liver perfusion mapping, mean value of PBV, and maximum value of PBV of tumor were significant in response assessment for per tumor and per patient (per tumor, all P < .001; per patient, P = .015, P = .001, P < .001, P = .020, and P = .032). Mean value of PBV of tumor was excellent for evaluating technical success with the highest C-statistic (0.880 and 0.920 for per tumor and per patient), followed by that of visual assessment of cone-beam CT–based liver perfusion mapping (0.864 and 0.908). ConclusionsCone-beam CT–based liver perfusion mapping provided reliable images to evaluate technical success after transarterial chemoembolization of HCC by qualitative visual assessment and quantitative perfusion values.

Robust Non-Rigid Motion Compensation of Free-Breathing Myocardial Perfusion MRI Data.

Kinetic parameter values, such as myocardial perfusion, can be quantified from dynamic contrast-enhanced magnetic resonance imaging data using tracer-kinetic modeling. However, respiratory motion affects the accuracy of this process. Motion compensation of the image series is difficult due to the rapid local signal enhancement caused by the passing of the gadolinium-based contrast agent. This contrast enhancement invalidates the assumptions of the (global) cost functions traditionally used in intensity-based registrations. The algorithms are unable to distinguish whether the differences in signal intensity between frames are caused by the spatial motion artifacts or the local contrast enhancement. In order to address this problem, a fully automated motion compensation scheme is proposed, which consists of two stages. The first of which uses robust principal component analysis (PCA) to separate the local signal enhancement from the baseline signal, before a refinement stage which uses the traditional PCA to construct a synthetic reference series that is free from motion but preserves the signal enhancement. Validation is performed on 18 subjects acquired in free-breathing and 5 clinical subjects acquired with a breath-hold. The validation assesses the visual quality, the temporal smoothness of tissue curves, and the clinically relevant quantitative perfusion values. The expert observers score the visual quality increased by a mean of 1.58/5 after motion compensation and improvement over the previously published methods. The proposed motion compensation scheme also leads to the improved quantitative performance of motion compensated free-breathing image series [30% reduction in the coefficient of variation across quantitative perfusion maps and 53% reduction in temporal variations (p < 0.001)].

Magnetic resonance cold pressor test to investigate potential endothelial dysfunction in patients suffering from type 1 diabetes.

In its course, diabetes impairs microvascular function through endothelial dysfunction. As the response of myocardial perfusion to sympathetic stimulation through cold is modulated by endothelium-related factors, an incipient endothelial dysfunction might be observed noninvasively by investigation of myocardial perfusion with a cold pressor test (CPT). This approach has been used in clinical MRI previously. To assess endothelial function of patients suffering from type 1 diabetes by MR CPT. Prospective cohort study. Twenty type 1 diabetics and 20 healthy volunteers. 3T, dynamic contrast enhanced perfusion (steady-state free precession). Absolute quantitative myocardial perfusion values at rest and under CPT. Kolmogorov-Smirnov test to determine normal distribution of the results. T-test for independent samples. Patients' mean myocardial perfusion was 0.68 cc/g/min at rest and 0.80 cc/g/min during CPT, respective values of 0.81 cc/g/min and 1.36 cc/g/min were found in healthy volunteers. Perfusion values differed significantly for CPT (P < 0.01) but not for resting conditions (P = 0.06). This study demonstrated that endothelial function might be impaired in type 1 diabetes patients. This fosters the thesis that endothelial function may serve as an early biomarker for coronary artery disease in patients with type 1 diabetes while these patients are still clinically asymptomatic. 2 Technical Efficacy: Stage 3 J. Magn. Reson. Imaging 2018;48:1595-1601.

Does Enhancement or Perfusion on Preprocedure CT Predict Outcomes After Embolization of Hepatocellular Carcinoma?

The objective of this study was to evaluate whether quantitative enhancement or perfusion measurements on preprocedure triphasic computed tomography (CT) can be used to predict response or overall survival after embolization of hepatocellular carcinoma. The institutional review board approved this retrospective review of 63 patients with hepatocellular carcinoma treated with particle embolization between March 2009 and December 2014. Quantitative enhancement and perfusion measurements were performed on the target tumor and the background liver on the triphasic CT performed before treatment. Microvascular invasion (MVI) and degree of differentiation were determined from a core biopsy specimen. Quantitative enhancement and perfusion values were then correlated with pathology (two-tailed t test), response to embolization on modified Response Evaluation Criteria In Solid Tumors (two-tailed t test), and overall survival after embolization (Cox proportional hazards model). Arterial enhancement did not predict immediate response or overall survival after embolization. The degree of differentiation or presence of MVI also did not predict immediate response or overall survival after embolization. However, high hepatic artery coefficient or low portal vein coefficient, both in the tumor (P = .011 and P = .004) and in the background liver (P = .015 and P = .009), were associated with worse survival. Hepatic artery coefficient, both in the tumor (P = .025) and in the background liver (P = .013), were independent predictors of survival in a multivariate model including the Child-Pugh score and the BCLC stage. Tumor and liver perfusion parameters estimated from preprocedure triphasic CT were predictive of survival after embolization. Arterial-phase enhancement and histology (degree of differentiation or MVI) did not predict immediate response or overall survival after particle embolization.

Comparison of perfusion models for quantitative T1 weighted DCE-MRI of rectal cancer

In this work, the two compartment exchange model and two compartment uptake model were applied to obtain quantitative perfusion parameters in rectum carcinoma and the results were compared to those obtained by the deconvolution algorithm. Eighteen patients with newly diagnosed rectal carcinoma underwent 3 T MRI of the pelvis including a T1 weighted dynamic contrastenhanced (DCE) protocol before treatment. Mean values for Plasma Flow (PF), Plasma Volume (PV) and Mean Transit Time (MTT) were obtained for all three approaches and visualized in parameter cards. For the two compartment models, Akaike Information Criterion (AIC) and {{boldsymbol{chi }}}^{{bf{2}}} were calculated. Perfusion parameters determined with the compartment models show results in accordance with previous studies focusing on rectal cancer DCE-CT (PF2CX = 68 ± 44 ml/100 ml/min, PF2CU = 55 ± 36 ml/100 ml/min) with similar fit quality (AIC:169 ± 81/179 ± 77, {{boldsymbol{chi }}}^{{bf{2}}}:10 ± 12/9 ± 10). Values for PF are overestimated whereas PV and MTT are underestimated compared to results of the deconvolution algorithm. Significant differences were found among all models for perfusion parameters as well as between the AIC and {{boldsymbol{chi }}}^{{bf{2}}} values. Quantitative perfusion parameters are dependent on the chosen tracer kinetic model. According to the obtained parameters, all approaches seem capable of providing quantitative perfusion values in DCE-MRI of rectal cancer.

Early response evaluation using CT-perfusion one day after transarterial chemoembolization for HCC predicts treatment response and long-term disease control

PurposeTo determine the value of CT perfusion (CTP) for early response assessment after transarterial chemoembolization (TACE) for hepatocellular carcinoma (HCC). Materials and methodsBetween April 2013 and April 2015, 41 HCC (16 patients) were included in this study. CT perfusion was performed before and one day after TACE. Blood flow (BF), blood volume (BV), time to start (TTS), arterial liver perfusion (ALP), portal liver perfusion (PVP) and hepatic perfusion index (HPI) were measured. Quantitative perfusion values before and after TACE were compared to the response assessed using mRECIST criteria six weeks after TACE and long-term outcome was assessed. ResultsTwenty-one lesions (51%) had complete remission (CR) and five (12%) had partial response (PR) six weeks after TACE. CTP parameters were significantly reduced after TACE in responders (PR, CR, p<0.001) while no difference was observed in non-responders. ALPpost was superior in the prediction of CR compared to BFpost and BVpost (p<0.001) with a sensitivity, specificity, PPV, NPV, and accuracy of 90%, 90%, 91%, 90%, and 91%, respectively. Only 3/21 lesions with CR recurred, with a mean local-recurrence-free survival of 19.6 months. ConclusionCT perfusion detects lesions with complete response one day after TACE, and is a feasible tool for early response assessment.

Iterative Reconstruction Improves Both Objective and Subjective Image Quality in Acute Stroke CTP.

PurposeComputed tomography perfusion (CTP) imaging in acute ischemic stroke (AIS) suffers from measurement errors due to image noise. The purpose of this study was to investigate if iterative reconstruction (IR) algorithms can be used to improve the diagnostic value of standard-dose CTP in AIS.MethodsTwenty-three patients with AIS underwent CTP with standardized protocol and dose. Raw data were reconstructed with filtered back projection (FBP) and IR with intensity levels 3, 4, 5. Image quality was objectively (quantitative perfusion values, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR)) and subjectively (overall image quality) assessed. Ischemic core and perfusion mismatch were visually rated. Discriminative power for tissue outcome prediction was determined by the area under the receiver operating characteristic curve (AUC) resulting from the overlap between follow-up infarct lesions and stepwise thresholded CTP maps.ResultsWith increasing levels of IR, objective image quality (SNR and CNR in white matter and gray matter, elimination of error voxels) and subjective image quality improved. Using IR, mean transit time (MTT) was higher in ischemic lesions, while there was no significant change of cerebral blood volume (CBV) and cerebral blood flow (CBF). Visual assessments of perfusion mismatch changed in 4 patients, while the ischemic core remained constant in all cases. Discriminative power for infarct prediction as represented by AUC was not significantly changed in CBV, but increased in CBF and MTT (mean (95% CI)): 0.72 (0.67–0.76) vs. 0.74 (0.70–0.78) and 0.65 (0.62–0.67) vs 0.67 (0.64–0.70).ConclusionIn acute stroke patients, IR improves objective and subjective image quality when applied to standard-dose CTP. This adds to the overall confidence of CTP in acute stroke triage.

Volumetric Arterial Spin-labeled Perfusion Imaging of the Kidneys with a Three-dimensional Fast Spin Echo Acquisition

Renal perfusion measurements using noninvasive arterial spin-labeled (ASL) magnetic resonance imaging techniques are gaining interest. Currently, focus has been on perfusion in the context of renal transplant. Our objectives were to explore the use of ASL in patients with renal cancer, and to evaluate three-dimensional (3D) fast spin echo (FSE) acquisition, a robust volumetric imaging method for abdominal applications. We evaluate 3D ASL perfusion magnetic resonance imaging in the kidneys compared to two-dimensional (2D) ASL in patients and healthy subjects. Isotropic resolution (2.6 × 2.6 × 2.8 mm(3)) 3D ASL using segmented FSE was compared to 2D single-shot FSE. ASL used pseudo-continuous labeling, suppression of background signal, and synchronized breathing. Quantitative perfusion values and signal-to-noise ratio (SNR) were compared between 3D and 2D ASL in four healthy volunteers and semiquantitative assessments were made by four radiologists in four patients with known renal masses (primary renal cell carcinoma). Renal cortex perfusion in healthy subjects was 284 ± 21 mL/100 g/min, with test-retest repeatability of 8.8%. No significant differences were found between the quantitative perfusion value and SNR in volunteers between 3D ASL and 2D ASL, or in 3D ASL with synchronized or free breathing. In patients, semiquantitative assessment by radiologists showed no significant difference in image quality between 2D ASL and 3D ASL. In one case, 2D ASL missed a high perfusion focus in a mass that was seen by 3D ASL. 3D ASL renal perfusion imaging provides isotropic-resolution images, with comparable quantitative perfusion values and image SNR in similar imaging time to single-slice 2D ASL.

Radiation dose reduction in cerebral CT perfusion imaging using iterative reconstruction

To investigate whether iterative reconstruction (IR) in cerebral CT perfusion (CTP) allows for 50% dose reduction while maintaining image quality (IQ). A total of 48 CTP examinations were reconstructed into a standard dose (150 mAs) with filtered back projection (FBP) and half-dose (75 mAs) with two strengths of IR (middle and high). Objective IQ (quantitative perfusion values, contrast-to-noise ratio (CNR), penumbra, infarct area and penumbra/infarct (P/I) index) and subjective IQ (diagnostic IQ on a four-point Likert scale and overall IQ binomial) were compared among the reconstructions. Half-dose CTP with high IR level had, compared with standard dose with FBP, similar objective (grey matter cerebral blood volume (CBV) 4.4 versus 4.3 mL/100 g, CNR 1.59 versus 1.64 and P/I index 0.74 versus 0.73, respectively) and subjective diagnostic IQ (mean Likert scale 1.42 versus 1.49, respectively). The overall IQ in half-dose with high IR level was scored lower in 26-31%. Half-dose with FBP and with the middle IR level were inferior to standard dose with FBP. With the use of IR in CTP imaging it is possible to examine patients with a half dose without significantly altering the objective and diagnostic IQ. The standard dose with FBP is still preferable in terms of subjective overall IQ in about one quarter of patients. • Computed tomography perfusion (CTP) is increasingly important in ischaemia imaging. • Radiation exposure of CTP is a drawback. • Iterative reconstruction (IR) allows reduction of radiation dose in unenhanced head CT. • CTP IR enables 50% dose reduction without altering objective and diagnostic quality.

Quantitative first‐pass perfusion MRI of the mouse myocardium

In this article, we present a first-pass perfusion imaging protocol to determine quantitative regional perfusion values (in mL min(-1) g(-1)) of the mouse myocardium. Perfusion was quantified using a Fermi-constrained deconvolution of the myocardial tissue response with the arterial input function. A dual-bolus approach was implemented. Experimental evidence is presented for the linearity of signal intensity in the left-ventricular lumen during the prebolus (r=0.99, P<0.001) and in the myocardium during the full-bolus injection (r=0.99, P<0.01) as function of Gd(DTPA)2- injection concentration used. The prebolus was used to reconstruct a nonsaturated arterial input function. Regional perfusion values proved repeatable in a cohort of nine healthy C57BL/6 mice. The perfusion values over two measurements with a 1-week interval were 7.3±0.9 and 7.2±0.6 mL min(-1) g(-1), respectively. No effects of time (P>0.05) and myocardial region (P>0.05) were observed. The between-session coefficient of variation was only 6%, whereas the inter-animal coefficient of variation was 11 and 8% for the separate experiments. We expect that the first-pass perfusion method here presented will be useful in preclinical studies of myocardial perfusion deficits and valuable to assess the impact of pro-angiogenic therapy after myocardial infarction.

The Value of Arterial Spin-Labeled Perfusion Imaging in Acute Ischemic Stroke

The purpose of this study was to evaluate the potential clinical value of arterial spin-labeled (ASL) perfusion MRI in acute ischemic stroke (AIS) through comparison with dynamic susceptibility contrast (DSC) enhanced perfusion MRI. Pseudocontinuous ASL with 3-dimensional background-suppressed gradient and spin echo readout was applied with DSC perfusion MRI on 26 patients with AIS. ASL cerebral blood flow and multiparametric DSC perfusion maps were rated for image quality and lesion severity/conspicuity. Mean ASL cerebral blood flow and DSC perfusion values were obtained in main vascular territories. Kendall coefficient of concordance was calculated to evaluate the reliability of ratings. Spearman correlation coefficients were calculated to compare ratings and quantitative perfusion values between ASL and DSC perfusion maps. ASL cerebral blood flow and DSC perfusion maps provided largely consistent results in delineating hypoperfused brain regions in AIS. Hyperemic lesions, which also appeared frequently in the AIS cases studied, were more conspicuous on ASL cerebral blood flow than on DSC cerebral blood flow, mean transit time and time to the maximum of the tissue residual function maps. As a rapid, noninvasive, and quantitative technique, ASL has clinical use in detecting blood flow abnormalities in patients with AIS.

The Relative Effect of Vendor Variability in CT Perfusion Results: A Method Comparison Study

There are known interoperator, intraoperator, and intervendor software differences that can influence the reproducibility of quantitative CT perfusion values. The purpose of this study was to determine the relative impact of operator and software differences in CT perfusion variability. CT perfusion imaging data were selected for 11 patients evaluated for suspected ischemic stroke. Three radiologists each independently postprocessed the source data twice, using four different vendor software applications. Results for cerebral blood volume (CBV), cerebral blood flow (CBF), and mean transit time (MTT) were recorded for the lentiform nuclei in both hemispheres. Repeated variables multivariate analysis of variance was used to assess differences in the means of CBV, CBF, and MTT. Bland-Altman analysis was used to assess agreement between pairs of vendors, readers, and read times. Choice of vendor software, but not interoperator or intraoperator disagreement, was associated with significant variability (p < 0.001) in CBV, CBF, and MTT. The mean difference in CT perfusion values was greater for pairs of vendors than for pairs of operators. Different vendor software applications do not generate quantitative perfusion results equivalently. Intervendor difference is, by far, the largest cause of variability in perfusion results relative to interoperator and intraoperator difference. Caution should be exercised when interpreting quantitative CT perfusion results because these values may vary considerably depending on the postprocessing software.

Automatic postprocessing for the assessment of quantitative human myocardial perfusion using MRI

Quantitative determination of myocardial perfusion currently involves time-consuming postprocessing. This retrospective study presents automatic postprocessing consisting of image registration and image segmentation to obtain regional signal intensity time courses and quantitative perfusion values. The automatic postprocessing was tested in 75 examinations in volunteers and patients, 57 at rest and 18 under adenosine-induced stress, and compared with a manual evaluation. In a substudy consisting of 10 examinations, the interobserver variability of the manual evaluation was investigated. Manual evaluation resulted in perfusion values with a median of 0.70 ml/g/min ranging from 0.03 to 3.68 ml/g/min. For all 75 examinations, the variability (standard deviation of the differences) between automatic and manual evaluation was 0.34 ml/g/min. Interobserver variability was of a similar order, 0.35 ml/g/min for all measurements. Automatic evaluation was successfully applied to all datasets giving results equivalent to manual evaluation. The time of user interaction for one single slice could be reduced from 25 min for manual evaluation to less than 1 min using the automatic algorithm. This reduction may allow quantitative magnetic resonance perfusion imaging to become a routine clinical procedure.

Magnetic resonance spin-labeling perfusion imaging of synovitis in inflammatory arthritis at 3.0 T

The aim of this study was to test the feasibility of arterial spin labeling (ASL) perfusion imaging of synovitis in inflammatory joint diseases on a clinical 3.0 T whole-body scanner. Fifteen patients (geometric mean 47 years, range 8-69 years) with different types of inflammatory arthritis of the finger or wrist joints participated in the study. In addition to conventional spin-echo and dynamic contrast-enhanced FLASH3D sequences, a novel spin-labeling technique (FAIR-TrueFISP) for quantitative assessment of tissue perfusion was applied. Perfusion maps were calculated pixel-wise by means of the extended Bloch equations. Perfusion maps showed good image quality with clear visualization of hyperaemia in synovitis. The computed perfusion maps corresponded best to subtraction images of the dynamic series from 30 to 60 s after contrast-medium injection. The quantitative perfusion values of synovitis showed a good correlation with the disease activity. Perfusion values for inflamed synovium in phase of high activity were up to 230 ml/100 g tissue/min. The proposed modality allows for the assessment of disease activity in arthritis without the application of contrast-medium offering a new tool for therapy monitoring. As the technique provides quantitative information on hyperaemia, it potentially offers new insights in the pathophysiology of arthritic diseases.