Regional myocardial blood volume and flow: first-pass MR imaging with polylysine-Gd-DTPA

Modeling regional myocardial flows from residue functions of an intravascular indicator

The purpose of the present study was to determine the accuracy and the sources of error in estimating regional myocardial blood flow and vascular volume from experimental residue functions obtained by external imaging of an intravascular indicator. For the analysis, a spatially distributed mathematical model was used that describes transport through a multiple-pathway vascular system. Reliability of the parameter estimates was tested by using sensitivity function analysis and by analyzing "pseudodata": realistic model solutions to which random noise was added. Increased uncertainty in the estimates of flow in the pseudodata was observed when flow was near maximal physiological values, when dispersion of the vascular input was more than twice the dispersion of the microvascular system for an impulse input, and when the sampling frequency was < 2 samples/s. Estimates of regional blood volume were more reliable than estimates of flow. Failure to account for normal flow heterogeneity caused systematic underestimates of flow. To illustrate the method used for estimating regional flow, magnetic resonance imaging was used to obtain myocardial residue functions after left atrial injections of polylysine-Gd-diethylenetriaminepentaacetic acid, an intravascular contrast agent, in anesthetized chronically instrumental dogs. To test the increase in dispersion of the vascular input after central venous injections, magnetic resonance imaging data obtained in human subjects were compared with left ventricular blood pool curves obtained in dogs. It is concluded that if coronary flow is in the normal range, when the vascular input is a short bolus, and the heart is imaged at least once per cardiac cycle, then regional myocardial blood flow and vascular volume may be reliably estimated by analyzing residue functions of an intravascular indicator, providing a noninvasive approach with potential clinical application.

Myocardial perfusion and function in dogs with moderate coronary stenosis

MRI studies of first-pass contrast enhancement with polylysine-Gd-DTPA and myocardial tagging using spatial modulation of magnetization (SPAMM) were performed to assess the feasibility of a combined regional myocardial blood flow and 2D deformation exam. Instrumented closed-chest dogs were imaged at a baseline control state (Cntl) followed by two interventions: moderate coronary stenosis (St) achieved by partial occlusion of the left anterior descending (LAD) and moderate coronary stenosis with dobutamine loading (StD). Hypoperfusion of the anterior region (ANT) of the myocardium (LAD distribution) relative to the posterior wall (POS) based on the upslope of the signal intensity time curve from the contrast-enhanced MR images was demonstrated only with dobutamine loading (ANT:POS Cntl = 1.077 +/- 0.15 versus ANT:POS StD = 0.477 +/- 0.11, P < 0.03) and was confirmed with radiolabeled microspheres measurements (ANT:POS Cntl = 1.18 +/- 0.2 ml/min/g versus ANT:POS StD = 0.44 +/- 0.1 ml/min/g; P < 0.002). Significant changes in regional myocardial shortening were only seen in the StD state (P < 0.02); the anterior region showed impaired myocardial shortening with dobutamine loading (P = NS), whereas the nonaffected POS region showed a marked increase in shortening when compared with Cntl (Cntl = 0.964 +/- 0.02 versus StD = 0.884 +/- 0.03; P < 0.001). These results demonstrate that an integrated quantitative assessment of regional myocardial function and semiquantitative assessment of myocardial blood flow can be performed noninvasively with ultrafast MRI.

Fast anatomical imaging of the heart and assessment of myocardial perfusion with arrhythmia insensitive magnetization preparation

A new contrast preparation based on modified driven equilibrium Fourier transfer is introduced and evaluated for generation of T1-weighted images for assessment of the myocardial perfusion with contrast agent first-pass kinetics. The new preparation scheme produces T1 contrast with insensitivity to arrhythmias in prospectively triggered sequential imaging thereby eliminating one of the major sources of problems in potential patient studies with previously employed contrast preparations schemes.