T2* measurement during first-pass contrast-enhanced cardiac perfusion imaging

ArticleinMagnetic Resonance in Medicine 56(5):1132-4 · November 2006with13 Reads
DOI: 10.1002/mrm.21061 · Source: PubMed
Abstract
First-pass contrast-enhanced (CE) myocardial perfusion imaging will experience T(2) (*) effects at peak concentrations of contrast agent. A reduction in the signal intensity of left ventricular (LV) blood due to T(2) (*) losses may effect estimates of the arterial input function (AIF) used for quantitative perfusion measurement. Imaging artifacts may also result from T(2) (*) losses as well as off-resonance due to the bolus susceptibility. We hypothesized that T(2) (*) losses would not be significant for measurement of the AIF in full-dose studies using a short echo time (TE = 0.6 ms). The purpose of this study was to directly measure T(2) (*) in the LV cavity during first-pass perfusion. For single-dose Gd-DTPA (0.1 mmol/kg at 5 ml/s), the LV blood pool T(2) (*) had a mean value of 9 ms (N = 10) at peak enhancement. Distortion of the AIF due to T(2) (*) signal intensity loss will be less than 10% using TE = 0.6 ms.
    • "Conventional cardiac perfusion acquisitions are based on a saturation recovery experiment followed by different readout strategies normally based on acquisition techniques for single-shot spoiled turbo field echo (TFE) or hybrid spoiled TFE echo planar imaging (TFE-EPI). TFE acquisition is normally desired since shorter echo times are achievable, thus making this approach less sensitive to R2* [29]. The signal model described in this report can be applied to both TFE and TFE-EPI. "
    [Show abstract] [Hide abstract] ABSTRACT: In-vivo quantification of cardiac perfusion is of great research and clinical value. The dual-bolus strategy is universally used in clinical protocols but has known limitations. The dual-saturation acquisition strategy has been proposed as a more accurate alternative, but has not been validated across the wide range of perfusion rates encountered clinically. Dual-saturation acquisition also lacks a clinically-applicable procedure for optimizing parameter selection. Here we present a comprehensive validation study of dual-saturation strategy in vitro and in vivo. The impact of saturation time and profile ordering in acquisitions was systematically analyzed in a phantom consisting of 15 tubes containing different concentrations of contrast agent. In-vivo experiments in healthy pigs were conducted to evaluate the effect of R2* on the definition of the arterial input function (AIF) and to evaluate the relationship between R2* and R1 variations during first-pass of the contrast agent. Quantification by dual-saturation perfusion was compared with the reference-standard dual-bolus strategy in 11 pigs with different grades of myocardial perfusion. Adequate flow estimation by the dual-saturation strategy is achieved with myocardial tissue saturation times around 100 ms (always <30 ms of AIF), with the lowest echo time, and following a signal model for contrast conversion that takes into account the residual R2* effect and profile ordering. There was a good correlation and agreement between myocardial perfusion quantitation by dual-saturation and dual-bolus techniques (R(2) = 0.92, mean difference of 0.1 ml/min/g; myocardial perfusion ranges between 0.18 and 3.93 ml/min/g). The dual-saturation acquisition strategy produces accurate estimates of absolute myocardial perfusion in vivo. The procedure presented here can be applied with minimal interference in standard clinical procedures.
    Full-text · Article · Dec 2015
    • "Non-uniform magnitude modulation response during data sampling can result in additional blurring. This effect is small when considering typical concentrations of CA found in the heart [12,13] , except possibly during the firstpass of Gd in the right ventricle due to its very short T2* at peak concentration. The modulation shape is approximately symmetric at the centre of k-space due to the centric phase order, avoiding edge enhancement artefacts. "
    [Show abstract] [Hide abstract] ABSTRACT: First-pass myocardial perfusion is often imaged with a tailored hybrid centric interleaved echo-planar-imaging sequence, providing rapid image acquisition with good contrast enhancement. The centric interleaved phase-encode order minimises the effective time-of-echo but it is sensitive to frequency-offsets. This short article aims to show possible artefacts that might originate with this sequence, in the context of first-pass perfusion imaging, when frequency-offsets are present. Non-uniform magnitude modulation effects were also analysed. Numerical and phantom simulations were used to illustrate the effects of frequency-offsets and non-uniform magnitude modulation with this sequence in a typical perfusion protocol. In vivo data was post-processed to analyse the h-EPI's sensitivity to the frequency-offsets. The centric phase-order was shown to be highly sensitive to frequency-offsets due to its symmetrical phase slope. Resulting artefacts include blurring, and splitting of the image into two identical copies along the phase-encode direction. It was also shown that frequency-offsets can introduce signal loss and ghosting of the right ventricle signal into the myocardium. The in vivo results were confirmed by numerical and phantom simulations. Magnitude modulation effects were found to be small. Imaging first-pass myocardial perfusion with an hybrid centric echo-planar-imaging sequence can be corrupted with ghosting and splitting of the image due to frequency-offsets.
    Full-text · Article · Jun 2012
    • "For example, measurements of regional myocardial blood flow (in ml/g/min) can be made using timeintensity curve deconvolution with a measured arterial input function (AIF), usually from the left ventricular cavity or ascending aorta[29,30]. Measurement of the true AIF is affected by short T1s and T2* effects[31] that occur with high contrast agent concentrations during bolus contrast agent passage in the blood pool. This has led to two imaging strategies: 1) the "dual-bolus" method[32,33], which involves AIF measurement during a separate lowdose injection (1/10 th or 1/20 th the dose) prior to the fulldose injection used for the measurement of myocardial enhancement and 2) the "dual-sequence" method343536, which replaces one of the imaging slices with an AIF measurement slice that employs an acquisition that avoids the saturation and T2* effects at high concentra- tions. "
    [Show abstract] [Hide abstract] ABSTRACT: In less than two decades, first-pass perfusion cardiovascular magnetic resonance (CMR) has undergone a wide range of changes with the development and availability of improved hardware, software, and contrast agents, in concert with a better understanding of the mechanisms of contrast enhancement. The following review provides a perspective of the historical development of first-pass CMR, the developments in pulse sequence design and contrast agents, the relevant animal models used in early preclinical studies, the mechanism of artifacts, the differences between 1.5T and 3T scanning, and the relevant clinical applications and protocols. This comprehensive overview includes a summary of the past clinical performance of first-pass perfusion CMR and current clinical applications using state-of-the-art methodologies.
    Full-text · Article · Feb 2008
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