Magnetic resonance in medicine : official journal of the Society of Magnetic Resonance in Medicine
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The prebolus technique allows one to quantify perfusion in the human heart with a low variability by means of MRI. In this study the prebolus technique was used to determine quantitative perfusion values in the human heart under adenosine stress and to measure the myocardial perfusion reserve (MPR). Twelve healthy volunteers were examined using the multislice prebolus technique with 1/4 cc Gd-BOPTA. ⋯ Myocardial perfusion was determined by deconvolution of the SI time courses with the arterial input function (AIF) from the prebolus scan. The mean stress perfusion value was 1.78 +/- 0.53 cc/g/min, and the mean rest perfusion was 0.52 +/- 0.11 cc/g/min, resulting in a mean MPR of 3.59 +/- 1.26. The measured values correlate well with data from animal models and human positron emission tomography (PET) studies.
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The magnetization-prepared rapid gradient-echo (MP-RAGE) sequence is well known and widely used for high-resolution, structural brain MRI. Here we present a new version, termed magnetization-prepared spiral acquisition gradient-echo (MP-SAGE), that employs interleaved square-spiral phase-encoding (PE) to take advantage of the 3D nature of the sequence. Resolution loss caused by point-spread function (PSF) blurring is circumvented by the use of variable flip angle (VFA) radiofrequency (RF) pulses. ⋯ Phantom results show excellent agreement between theory and experiment for substances with relaxation times similar to those of human brain tissue. Both phantom and in vivo results show a strong enhancement of SNR and CNR compared to the standard MP-RAGE in high-resolution MRI. The benefits for brain tissue segmentation using images obtained with MP-SAGE are shown.
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Three-dimensional spin-lattice relaxation time in the rotating frame (3D-T1rho) with parallel imaging at 3.0T was implemented on a whole-body clinical scanner. A 3D gradient-echo sequence with a self-compensating spin-lock pulse cluster was combined with generalized autocalibrating partially parallel acquisitions (GRAPPA) to acquire T1rho-weighted images. 3D-T1rho maps of an agarose phantom and three healthy subjects were constructed using an eight-channel phased-array coil without parallel imaging and with parallel imaging acceleration factors of 2 and 3, in order to assess the reproducibility of the method. The coefficient of variation (CV) of the median T1rho of the agarose phantom was 0.44%, which shows excellent reproducibility. ⋯ The CV of the median T1rho of the patellar cartilage varied between approximately 1.1% and 4.3%. Similarly, the CV varied between approximately 2.1-5.8%, approximately 1.4-8.7%, and approximately 1.5-4.1% for the biceps femoris and lateral and medial gastrocnemius muscles, respectively. The preliminary results demonstrate that 3D-T1rho maps can be constructed with good reproducibility using parallel imaging. 3D-T1rho with parallel imaging capability is an important clinical tool for reducing both the total acquisition time and RF energy deposition at 3T.
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Viability detection is crucial for the management of myocardial infarction (MI). Signal intensity (SI)-based MRI methods may overestimate infarct size in vivo. In contrast to SI, the longitudinal relaxation-rate enhancement (DeltaR1) is an intrinsic parameter that is linearly proportional to the concentration of contrast agent (CA). ⋯ Median deviations from the true infarction fraction (IF) were 1.23% and 0.49% of LV at 24 hr and 48 hr, respectively. No significant difference was found between PIM24 hr and PIM48 hr. DeltaR1-based PIM is an accurate and reproducible method for quantifying myocardial viability distribution, and thus enhances the clinical utility of CE-MRI.
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Arterial spin labeling (ASL) MRI is a useful technique for noninvasive measurement of cerebral blood flow (CBF) in humans. High field strength provides a unique advantage for ASL because of longer blood T(1) relaxation times, making this technique a promising quantitative approach for functional brain mapping. However, higher magnetic field also introduces new challenges. ⋯ If not accounted for, such an effect can complicate the interpretation of the ASL results, e.g., causing a delayed onset and offset of the response, or inducing an artifactual poststimulus undershoot. The BOLD contribution also decreases the sensitivity of ASL-based fMRI. Correction methods are proposed to reduce the artifact, giving increased number of activated voxels (18+/-5%, P=0.006) and more accurate estimation of CBF temporal characteristics.