Importance of perfusion in myocardial viability studies using delayed contrast-enhanced magnetic resonance imaging

PURPOSE: To investigate whether an extracellular gadolinium-(Gd)-based contrast agent (CA) enters nonperfused myocardium during acute coronary occlusion, and whether nonperfused myocardium presents as hyperintense in delayed contrast-enhanced (DE) MR images in the absence of CA in that region. MATERIALS AND METHODS: The left anterior descending coronary artery (LAD) was occluded for 200 minutes in six pigs. The longitudinal relaxation rate (R(1)) in blood, perfused myocardium, and nonperfused myocardium was repeatedly measured using a Look-Locker sequence before and during the first hour after administration of Gd-DTPA-BMA. RESULTS: While blood and perfused myocardium showed a major increase in R(1) after CA administration, nonperfused myocardium did not. R(1) in nonperfused myocardium was significantly lower than in blood and perfused myocardium during the first hour after CA administration. When the signal from perfused myocardium was nulled, demarcation of the hyperintense nonperfused myocardium was achieved in all of the study animals. CONCLUSION: Gd-DTPA-BMA does not enter ischemic myocardium within one hour after administration during acute coronary occlusion. The ischemic region with complete absence of CA still appears bright when the signal from perfused myocardium is nulled using inversion-recovery DE-MRI. This finding is important for understanding the basic pathophysiology of inversion-recovery viability imaging, as well as for imaging of acute coronary syndromes.     

Cerebral perfusion imaging using contrast-enhanced MRI

New developments in fast magnetic resonance imaging (MRI) have enabled imaging of cerebral haemodynamics. This article describes the theory behind perfusion imaging and provides an overview of the most commonly used MRI technique. Limitations of this technique are described, and the potential clinical applications are discussed, with particular attention to the role of perfusion imaging in the context of stroke and brain tumour.     

Auto-SENSE perfusion imaging of the whole human heart

PURPOSE: To show the application of auto-sensitivity encoding (SENSE)-a self-calibrating parallel imaging technique-to first pass perfusion imaging of the whole human heart. MATERIALS AND METHODS: The self-calibrating parallel imaging method auto-SENSE was implemented for a saturation recovery turbo-fast low-angle shot (FLASH) sequence on a 1.5-T scanner using a standard four-element body phased array coil. By reducing the acquisition time per slice by a factor of two compared to conventional turbo FLASH imaging, the number of imaged slices could be doubled to six to ten with an unchanged temporal resolution of one image per heartbeat. This technique has been tested in eight healthy volunteers for contrast-enhanced heart perfusion imaging. RESULTS: Auto-SENSE heart perfusion imaging with improved coverage of the human heart could be performed successfully in all volunteers. A first quantitative comparison of perfusion values between the auto-SENSE and the non-SENSE techniques shows good agreement. CONCLUSION: Auto-SENSE allows perfusion imaging of the whole human heart without gaps.     

Dynamic susceptibility contrast-enhanced perfusion magnetic resonance (MR) imaging combined with contrast-enhanced MR imaging in the follow-up of immunogene-treated glioblastoma multiforme

Purpose: To assess the value of the combined use of dynamic susceptibility contrast-enhanced perfusion magnetic resonance imaging (MRI) and conventional contrast-enhanced MRI for the follow-up of treatment of glioblastoma multiforme (GBM).

Material and Methods: 79 examinations were performed in six surgically and immunogene-treated patients and two surgically treated patients. Ratios of the relative cerebral blood volume (rCBV) in lesions and in the contralateral normal-appearing white matter were calculated. The regions with elevated rCBV were compared with those with contrast enhancement. Tissue specimens from surgical biopsies and autopsies were studied histopathologically.

Results: The lesion-to-normal rCBV ratios were high in the tumors prior to operation (7.3 to 18.2) as well as in the recurrent tumors (1.6 to 13.2). The volumes of the regions with elevated rCBV were similar to those with contrast enhancement in 63 of the 79 examinations. However, in 11 of 79 examinations, the regions with high rCBV were smaller than the regions with contrast enhancement (“mismatch”). In two samples from the immunogene-treated patients this was correlated with the histopathological finding of malignant tumor with numerous proliferating GBM vessels with multiple minimal lumina, sometimes thrombotized or ruptured. These vessels may have increased permeability with contrast enhancement not accompanied by increased microvascular volume.

Conclusion: 1) Elevated rCBV on perfusion MRI corresponding to the contrast-enhancing lesion supports the diagnosis of recurrent malignant tumor. 2) A mismatch showing a volume of rCBV elevation smaller than that of contrast enhancement can be seen in particularly aggressive tumor growth and is thus not always a sign of reactive non-tumor changes. 3) The combination of perfusion MRI and conventional contrast MRI provides useful information in the follow-up of glioblastoma multiforme treatment.     

Multislice first-pass myocardial perfusion imaging on a conventional clinical scanner

A technique is demonstrated for the acquisition and processing of multislice, first-pass contrast-enhanced pelfusion images in the myocardium. The acquisition is a modification of “keyhole” imaging in which time series images are acquired by sampling a limited segment of k-space, corresponding to the low spatial frequencies. In the modification demonstrated here, keyhole samples are divided into two groups that are sampled on alternate cardiac cycles. The alternate “missing” k-space portions are synthesized by Fourier interpolation. Visualization of contrast agent accumulation by image subtraction is demonstrated. A motion artifact reduction process using time domain Fourier filtering is used to reduce artifacts from respiration. Studies were performed on 46 patients at 1.5 T using gadoteridol (0.05–0.1 mmol/kg) injected into the right antecubital vein in conjunction with radionuclide imaging. Fully concordant studies were noted in 27 of these patients. Remaining studies were either partially or completely discordant for reasons relating to the differing natures of radionuclide versus MR contrast agent characteristics.     

Comparison of three accelerated pulse sequences for semiquantitative myocardial perfusion imaging using sensitivity encoding incorporating temporal filtering (TSENSE)

PURPOSE: To investigate the parallel acquisition technique sensitivity encoding incorporating temporal filtering (TSENSE) with three saturation-recovery (SR) prepared pulse sequences (SR turbo fast low-angle shot [SR-TurboFLASH], SR true fast imaging with steady precession [SR-TrueFISP], and SR-prepared segmented echo-planar-imaging [SR-segEPI]) for semiquantitative first-pass myocardial perfusion imaging. MATERIALS AND METHODS: In blood- and tissue-equivalent phantoms the relationship between signal intensity (SI) and contrast-medium concentration was evaluated for the three pulse sequences. In volunteers, signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and normalized upslopes (NUS) were calculated from signal-time curves (STC). Moreover, artifacts, image noise, and overall image quality were qualitatively evaluated. RESULTS: Phantom data showed a 40% increased linear range of the relation between SI and contrast-medium concentration with TSENSE. In volunteers, TSENSE introduced significantly residual artifacts and loss in SNR and CNR. No differences were found for NUS values with TSENSE. SR-TrueFISP yielded highest SNR, CNR, and quality scores. However, in SR-True-FISP images, dark-banding artifacts were most pronounced. NUS values obtained with SR-TrueFISP were significantly higher and with SR-segEPI significantly lower than with SR-TurboFLASH. CONCLUSION: Semiquantitative myocardial perfusion imaging can significantly benefit from TSENSE due to shorter acquisition times and increased linearity of the pulse sequences. Among the three pulse sequences tested, SR-TrueFISP yielded best image quality. SR-segEPI proved to be an interesting alternative due to shorter acquisition times, higher linearity and fewer dark-banding artifacts.     

Single- or dual-bolus approach for the assessment of myocardial perfusion reserve in quantitative MR perfusion imaging.

A dual-bolus protocol can overcome limitations due to T1-induced MR signal attenuation and hence enables more accurate quantification of myocardial blood flow (MBF) by contrast enhanced MR perfusion imaging. The study explores potential benefits of the dual-bolus technique for the assessment of myocardial perfusion reserve (MPR) over a standard single-bolus protocol. Nineteen patients without obstructive coronary artery disease as assessed by cardiac catheterization underwent a stress-rest MR perfusion study using a dual-bolus protocol. Gd-DTPA dosages of 0.005 and 0.05 mmol/kg of bodyweight were delivered as pre- and main-bolus. For comparison arterial input curves where extracted from left ventricular cavity passage including both, pre-bolus and main-bolus data. Global and segmental MPR were determined from semiquantitative and from full quantitative measures of MBF. As a result good agreement between dual- and single-bolus technique was found with relative differences of maximally 10% in global MPR estimates. For the dual bolus approach a significant relative decrease of 30% (P<0.001) was found for the coefficient of segmental MPR variation, which may allow a more reliable detection of hypoperfused segments in clinical studies.     

Comparison of different contrast agents and doses for quantitative MR myocardial perfusion imaging

PURPOSE: To investigate three different contrast agents at different injection volumes for repetitive quantitative multislice myocardial perfusion imaging using the prebolus technique. MATERIALS AND METHODS: Two consecutive prebolus perfusion measurements were performed on a 1.5 T scanner using identical injection volumes for the first and second examination to test the reproducibility for possible rest and stress examination in normal volunteers. Either 1-8 mL, 1-12 mL Gd-DTPA, 1-4 mL, 1-6 mL, 1-9 mL Gd-BOPTA, or 1-4 mL, 1-6 mL gadobutrol were applied. RESULTS: In cases where injection volumes were sufficiently small, there was no indication of significant differences in quantitative perfusion values with respect to the different contrast agents. Increasing the bolus volume improved the contrast-to-noise ratio (CNR) but led to saturation effects and underestimation of the true perfusion. The highest CNR was measured for gadobutrol (6 mL, p < 0.0005 compared to 8 mL Gd-DTPA). The smallest difference of perfusion values between the first and the second prebolus examination was found for Gd-BOPTA (p < or = 0.006 compared Gd-DTPA). CONCLUSION: Prebolus examinations for quantitative myocardial perfusion imaging are possible with all three contrast agents for sufficient small injection volumes. Gd-BOPTA was found to be advantageous for a combined quantitative rest and stress examination.     

Quantitative myocardial perfusion analysis with a dual-bolus contrast-enhanced first-pass MRI technique in humans

PURPOSE: To compare fully quantitative and semiquantitative analysis of rest and stress myocardial blood flow (MBF) and myocardial perfusion reserve (MPR) using a dual-bolus first-pass perfusion MRI method in humans. MATERIALS AND METHODS: Rest and dipyridamole stress perfusion imaging was performed on 10 healthy humans by administering gadolinium contrast using a dual-bolus protocol. Ventricular and myocardial time-signal intensity curves were generated from a series of T1-weighted images and adjusted for surface-coil intensity variations. Corrected signal intensity curves were then fitted using fully quantitative model constrained deconvolution (MCD) to quantify MBF (mL/min/g) and MPR. The results were compared with semiquantitative contrast enhancement ratio (CER) and upslope index (SLP) measurements. RESULTS: MBF (mL/min/g) estimated with MCD averaged 1.02 +/- 0.22 at rest and 3.39 +/- 0.59 for stress with no overlap in measures. MPR was 3.43 +/- 0.71, 1.91 +/- 0.65, and 1.16 +/- 0.19 using MCD, SLP, and CER. Both semiquantitative parameters (SLP and CER) significantly underestimated MPR (P < 0.001) and failed to completely discriminate rest and stress perfusion. CONCLUSION: Rest and stress MBF (mL/min/g) and MPR estimated by dual-bolus perfusion MRI fit within published ranges. Semiquantitative methods (SLP and CER) significantly underestimated MPR.     

Multislice first-pass myocardial perfusion imaging: Comparison of saturation recovery (SR)-TrueFISP-two-dimensional (2D) and SR-TurboFLASH-2D pulse sequences

PURPOSE: To compare signal-to-noise ratio (SNR), contrast-to-noise (CNR) ratio, and diagnostic accuracy of a newly developed saturation recovery (SR)-TrueFISP-two-dimensional (2D) sequence with an SR-TurboFLASH-2D sequence. MATERIALS AND METHODS: In seven healthy subjects and nine patients with coronary artery disease (CAD), contrast-enhanced perfusion imaging (with Gd-DTPA) was performed with SR-TrueFISP and SR-TurboFLASH sequences. Hypoperfused areas were assessed qualitatively (scale = 0-4). Furthermore, SNR and CNR were calculated and semiquantitative perfusion parameters were determined from signal intensity (SI) time curves. Standard of reference for patient studies was single-photon emission computer tomography (SPECT) and angiography. RESULTS: The perception of perfusion deficits was superior in TrueFISP images (2.6 +/- 1.0) than in TurboFLASH (1.4 +/- 0.6) (P < 0.001). Phantom measurements yielded increased SNR (143 +/- 34%) and CNR (158 +/- 64%) values for TrueFISP. In patient/volunteer studies SNR was 61% to 100% higher and signal enhancement was 110% to 115% higher with TrueFISP than with TurboFLASH. Qualitative and semiquantitative assessment of perfusion defects yielded higher sensitivities for detection of perfusion defects with TrueFISP (68% to 78%) than with TurboFLASH (44% to 59%). CONCLUSION: SR-TrueFISP-2D perfusion imaging provides superior SNR and CNR than TurboFLASH imaging. Moreover, the dynamic range of SIs was found to be higher with TrueFISP, resulting in an increased sensitivity for detection of perfusion defects.     

Regional pulmonary perfusion using model-free analysis of contrast-enhanced MRI in meconium-aspirated piglets

PURPOSE: To investigate if dynamic contrast-enhanced MRI in lungs could add new information to pulmonary hypertension in a newborn piglet model. MATERIALS AND METHODS: Six newborn piglets were subjected to instillation of meconium following treatment with sildenafil. Before and after both of these events, dynamic contrast-enhanced MRI was performed to determine pulmonary blood flow (PBF) using a model-free deconvolution of the dynamic signal-time curve, together with invasive measurements of mean airway pressure (PAW), cardiac output (CO), and oxygenation index (OI). RESULTS: Meconium instillation caused a significant increase in PAW (P < 0.05) accompanied by a marked increase in OI, the average PBF in the four lung regions (apical-anterior, apical-posterior, distal-anterior, and distal-posterior) decreased significantly by 33% (P < 0.001), but it did not significantly affect CO. On the other hand, infusion of sildenafil caused a significant increase in CO (P < 0.01), and administration resulted mainly in an increased PBF in the distal parts of the lungs. CONCLUSION: By using dynamic contrast-enhanced MRI, we demonstrated a marked decrease in PBF following instillation of meconium, which was not followed by an equivalent decrease in CO, suggesting that measurements of CO inadequately reflect the intrapulmonary changes in the blood circulation.     

Dynamic contrast-enhanced magnetic resonance imaging: a useful tool for characterizing ovarian epithelial tumors

PURPOSE: To evaluate the utility of dynamic contrast enhancement (DCE) MRI for distinguishing among benign, borderline and invasive epithelial ovarian tumors. MATERIALS AND METHODS: We analyzed preoperative MRI studies of 37 patients with ovarian epithelial tumors (10 benign, 11 borderline, and 16 invasive). A DCE-MRI sequence was acquired and regions of interest (ROIs) were drawn in the ovarian tumors and adjacent myometrium. A total of three patterns of enhancement were defined. Dynamic data were parameterized using mathematical models that included the enhancement amplitude (EA), the time of half rising (THR), and the maximal slope (MS). Using myometrium as the internal reference, ratios of EA (EAr), THR (THRr), MS (MSr), and initial area under the curve for 60 seconds after injection (IAUC(60) ratio) were determined. RESULTS: Morphological criteria such as septa, papillary projection, solid portion, and T2-weighted MR signal intensity of solid tissue were useful for discriminating invasive from noninvasive ovarian tumors (P = 0.01, P = 0.02, P = 0.002, and P < 0.0001 respectively) but not for discriminating benign from borderline tumors. Curve type 3 was specific for invasive ovarian tumors. EAr, MSr, and IAUC(60) ratio were higher for invasive than for benign (P < 0.0001) and borderline tumors (P = 0.005, P = 0.002, and P = 0.001, respectively). The IAU(60) ratio was the most relevant factor for discriminating benign from borderline and invasive tumors. MSr and IAU(60) ratio could be combined to generate a decision tree with 81% accuracy. CONCLUSION: DCE-MRI is a useful tool for characterizing epithelial ovarian tumors.     

Quantitative analysis of transmural gradients in myocardial perfusion magnetic resonance images

Conventional quantitative assessments of myocardial perfusion analyze the temporal relation between the arterial input function and the myocardial signal intensity curves, thereby neglecting the important spatial relation between the myocardial signal intensity curves. The new method presented in this article enables characterization of sub‐endocardial to sub‐epicardial gradients in myocardial perfusion based on a two dimensional, “gradientogram” representation, which displays the evolution of the transmural gradient in myocardial contrast uptake over time in all circumferential positions of the acquired images. Moreover, based on segmentation in these gradientograms, several new measurements that characterize transmural myocardial perfusion distribution over time are defined. In application to clinical image data, the new two‐dimensional representations, as well as the newly defined measurements revealed a clear distinction between normal perfusion and inducible ischaemia. Thus, the new measurements may serve as diagnostic markers for the detection and characterization of epicardial coronary and microvascular disease. Magn Reson Med, 2011. © 2011 Wiley Periodicals, Inc.     

Dynamic contrast-enhanced myocardial perfusion MRI accelerated with k-t sense.

In the k-t sensitivity encoding (k-t SENSE) method spatiotemporal data correlations are exploited to accelerate data acquisition in dynamic MRI studies. The present study demonstrates the feasibility of applying k-t SENSE to contrast-enhanced myocardial perfusion MRI and using the speed-up to increase spatial resolution. At a net acceleration factor of 3.9 (k-t factor of 5 with 11 training profiles) accurate representations of dynamic signal intensity (SI) changes were achieved in computer simulations. In vivo, 5x k-t SENSE was compared with 2x SENSE (identical acquisition parameters except for in-plane spatial resolution = 1.48 x 1.48 mm(2) vs. 2.64 x 2.64 mm(2), respectively). In 10 volunteers no differences in myocardial SI profiles were found (relative peak enhancement = 151% vs. 149.7%, maximal upslope = 12.9%/s vs. 13.3%/s for 2x SENSE and 5x k-t SENSE, respectively, all P > 0.05). Overall image quality was similar, but endocardial dark rim artifacts were reduced with k-t SENSE. Signal-to-noise ratio (SNR) in the myocardium was greater with 5x k-t SENSE by a factor of 1.36 +/- 0.23 at peak contrast enhancement with the relative yield decreasing with increasing dynamics in the object in accordance to theory. Higher nominal acceleration factors of up to 10-fold were shown to be feasible in computer simulations and in vivo.     

门控断层显像在心肌灌注断层显像中的应用

使用门控心肌断层显像不但减低了心脏搏动产生的图像边缘模糊,提高了对心肌缺血诊断的灵敏度和特异性,而且通过傅立叶变换和图像边缘识别技术等图像处理技术,可以在一次采集的信息基础上同时获得心脏的心肌血流灌注、心肌活力、室壁运动、射血功能和收缩协调性等参数,提高了核素心脏检查的价值,为临床准确判断患者的心脏状况,选择治疗方案,预后及疗效评价提供了更可靠的数据。本文就其近年来的临床应用进行综述。     

Continuous arterial spin-labeling perfusion magnetic resonance imaging of the human testis

RATIONALE AND OBJECTIVES: The purpose of this study was to determine if continuous arterial spin-labeling perfusion magnetic resonance imaging could be used to detect testicular perfusion in human subjects. MATERIALS AND METHODS: Continuous arterial spin-labeling magnetic resonance perfusion imaging was performed in seven normal male volunteers and in one patient with a painful scrotum following vasectomy. RESULTS: Normal testicular blood flow was demonstrated in 14 of 14 normal testes in seven volunteers, as well as in two normally perfused testes in the post-vasectomy patient. A change in the steady state magnetization was observed in all of the normally perfused testes of the seven volunteers. CONCLUSION: It is possible to detect blood flow to the normally perfused testes using noninvasive spin-labeling perfusion magnetic resonance imaging. This modality could potentially, in future investigations, be used to image patients with suspected testicular torsion and resultant testicular ischemia.     

Exercise training increases myocardial perfusion in residual viable myocardium within infarct zone

Purpose:

To study the effect of exercise training on the myocardial perfusion in the postinfarct myocardium.

Materials and Methods:

Twenty‐nine patients with stable chronic myocardial infarction were randomly assigned to either a training group (N = 17) or a control group (N = 12). The training group received a 3‐month exercise program. Cardiovascular MR was first performed before the training to establish a baseline, and subsequently performed once again upon conclusion of the program. Late gadolinium enhancement was used both to define the infarct and remote zones and to quantify the ratio of the residual viable myocardium (VMR) within the infarct zone. The myocardium was divided into subendocardial and subepicardial layers with equal thickness. The interval change of myocardial perfusion reserve (MPR) was computed for each zone and layer. The association between the exercise‐induced perfusion change and VMR was analyzed for layers of the infarct zone.

Results:

In the training group, the remote zone showed significantly increased MPR. The infarct zone showed no perfusion change in the subendocardial layer, but it demonstrated significantly increased MPR in the subepicardial layer. In the infarct zone, the change in MPR was associated with VMR.

Conclusion:

In chronic myocardial infarction, the exercise‐induced perfusion change in the infarct zone is proportional to the amount of residual viable myocardium. J. Magn. Reson. Imaging 2011;. © 2011 Wiley‐Liss, Inc.     

Calf muscle perfusion at peak exercise in peripheral arterial disease: measurement by first-pass contrast-enhanced magnetic resonance imaging

PURPOSE: To develop a contrast-enhanced magnetic resonance (MR) technique to measure skeletal muscle perfusion in peripheral arterial disease (PAD). MATERIALS AND METHODS: A total of 11 patients (age = 61 +/- 11 years) with mild to moderate symptomatic PAD (ankle-brachial index [ABI] = 0.75 +/- 0.08) and 22 normals were studied using an MR-compatible ergometer. PAD and normal(max) (Nl(max); N = 11) exercised to exhaustion. Nl(low) (N = 11) exercised to the same workload achieved by PAD. At peak exercise, 0.1 mm/kg of gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) was infused at 3-4 cm(3)/second followed by a saline flush at the same rate. A dual-contrast gradient echo (GRE) sequence enabled simultaneous acquisition of muscle perfusion and arterial input function (AIF). The perfusion index (PI) was defined as the slope of the time-intensity curve (TIC) in muscle divided by the arterial TIC slope. RESULTS: Median workload was 120 Joules in PAD, 210 Joules in Nl(low), and 698 Joules in Nl(max) (P < 0.001 vs. Nl(low) and PAD). Median PI was 0.29 in PAD (25th and 75th percentiles [%] = 0.20, 0.40), 0.48 in Nl(low) (25th, 75th % = 0.36, 0.62; P < 0.02 vs. PAD), and 0.69 in Nl(max) (25th, 75th % = 0.5, 0.77; P < 0.001 vs. PAD). Area under the ROC-curve for PI differentiating patients from Nl(max) was 0.95 (95% confidence interval [CI] = 0.77-0.99). CONCLUSION: Peak-exercise measurement of lower limb perfusion with dual-contrast, first-pass MR distinguishes PAD from normals. This method may be useful in the study of novel therapies for PAD.     

Factor analysis of medical image sequences improves evaluation of first-pass MR imaging acquisitions for myocardial perfusion

RATIONALE AND OBJECTIVES: Factor analysis of medical image sequences (FAMIS) applied to gadolinium chelate-enhanced subsecond magnetic resonance (MR) imaging was evaluated as a postprocessing method for assessing myocardial perfusion in coronary artery disease (CAD). MATERIALS AND METHODS: To assess the accuracy of motion correction, five normal volunteers underwent MR imaging at rest. Thirteen patients with well-documented CAD and no myocardial infarction underwent MR imaging at rest and after dipyridamole administration. After motion correction, a single myocardial tissue factor (FAMISt) image was obtained with FAMIS for each raw MR imaging series acquisition. To evaluate how FAMIS could improve the analysis of these acquisitions, five readers visually assessed myocardial perfusion with FAMISt and raw MR images, and a multicase, multireader receiver operating characteristic analysis was performed. RESULTS: FAMISt images significantly improved detection of the perfusion defects when compared with raw MR images (P = .002). Areas under the receiver operating characteristic curves ranged from 0.84 to 0.93 with FAMISt images and from 0.48 to 0.85 with raw MR images. CONCLUSION: FAMIS applied to first-pass MR imaging series provided myocardial perfusion images that improve the objective assessment of myocardial perfusion in patients with CAD.