Quantification of resting myocardial blood flow in a pig model of acute ischemia based on first‐pass MRI

Abstract

Qualitative and semiquantitative contrast-enhanced (CE) dynamic perfusion MRI techniques are established as noninvasive diagnostic means of assessing coronary artery disease. However, to date quantification of myocardial blood flow (MBF) has not reached the same acceptance as MBF quantification with nuclear techniques. To validate quantification of MBF at rest using the extracellular contrast agent (CA) Gd-DTPA, we performed an animal study in a pig model of acute myocardial ischemia. We quantified MBF from MRI data with a mathematical model ( Most clinical studies are based on the use of extracellular CAs, such as Gd-DTPA. Several methods have been described for the quantification of MBF with Gd-DTPA (5,6). Preliminary results from studies using a two-compartment model consisting of a vascular compartment volume and the interstitial space have shown that quantification of MBF with the extracellular CA Gd-DTPA should be possible (7).However, to date quantification of resting MBF with Gd-DTPA and the MMID4 model has not been validated. Therefore, the objective of this study was to validate MBF quantification with the clinically available CA Gd-DTPA and the MMID4 model in a pig model of acute ischemia. MATERIALS AND METHODSWith the approval of the local animal care committee, we performed this study in an open-chest pig model of acute myocardial ischemia (n ϭ 6; weight ϭ 24 -30 kg). The pigs were ventilated with supplemental oxygen and anesthetized with thiopental sodium before a left-side thoracotomy was performed. The proximal left anterior descending coronary artery (LAD) was dissected free, and a mechanical occluder was wrapped around the artery. During the perfusion measurements the diameter of the artery was reduced manually. Simultaneously, blood flow in the LAD was measured with a ultrasound transit time flow meter (CM1000; Medi-Stim, Oslo, Norway).In each animal, perfusion measurements were performed during normal LAD blood flow and during two different degrees of LAD stenosis. To achieve the two degrees of stenosis, the mechanical occluder was adjusted under control of the transit time flow meter. LAD blood flow values of approximately 50% and 25% of the blood flow value measured without occlusion were obtained. To achieve stable blood flow conditions in the LAD, the degree of the stenosis was kept fixed for at least 30 min before the MRI and microsphere perfusion measurements were performed.At each perfusion state (normal blood flow in the LAD, and at both degrees of LAD stenosis) a reference perfusion measurement was performed with the use of microspheres (10). For this purpose, fluorescent microspheres (Triton Technology Inc., San Diego, CA, USA) were injected via a left arterial catheter (11) prior to the MRI perfusion measurements. We were able to obtain more than one microsphere blood flow measurement in each animal by using different colors of fluorescent microspheres. To allow calculation of absolute blood flow rates, a reference blood sample of 10 ml was taken from the abdominal aorta over a per...

Quantitative myocardial perfusion measurement using CT Perfusion: a validation study in a porcine model of reperfused acute myocardial infarction

“…Both J-W and MMID4 model can determine MBF independent of E but the J-W model is mathematically less complicated and is characterized by 5 [9] instead of over 20 parameters [33]. To avoid unreliable estimation of MBF because of overfitting with the MMID4 model [34], most of the model parameters except for MBF, E and a few others have to fixed [35][36][37]. In practice, J-W and MMID4 model are equivalent as evidenced by the similar linear correlation relationship of MBF measured with DCE-CT versus microspheres in this study and that of ref 4 (slope 0.96 vs. 0.88 and intercept 0.30 vs. 0.75).…”

Critical Single Proximal Left Arterial Descending Coronary Artery Stenosis to Mimic Chronic Myocardial Ischemia: A New Model Induced by Minimal Invasive Technology

“…In our present study, setting coronary flow was differentiated in angiographically TIMI II slow and fast flow, thus allowing the evaluation of the hemodynamic status of the stenosis in relation to regional myocardial function [9]. Clearly, SPECT analysis documented myocardial hypoperfusion, but noninvasive blood flow quantification might be more reliably accomplished by using MRI in future experiments [27]. …”

Quantitative myocardial CT perfusion: a pictorial review and the current state of technology development

“…As such, MMID4 is a more realistic model than J&W to describe the kinetic behavior of contrast solute in the myocardium. Most of the parameters modeled by MMID4 need to be fixed, however, except F and E and a few others 27,28 to avoid unreliable estimation of MP owing to overfitting the measured data. 29 For instance, x-ray contrast agents are hydrophilic and inert, hence contrast distribution in parenchyma and metabolization in other spaces can be ignored.…”