State-of-the-art-myocardial perfusion stress testing: Static CT perfusion

Large multicenter studies and meta-analysis have documented the diagnostic accuracy and the prognostic implications of stress echocardiography, cardiac magnetic resonance and, mainly, nuclear stress tests. However, none of them provides a comprehensive anatomical and functional evaluation within the same study as stress CT perfusion. Myocardial CT perfusion is the only non-invasive modality that allows to quantifying coronary stenosis and determining its functional relevance, constituting a potential “one-stop-shop” method for the diagnosis and global management of patients with known or suspected coronary artery disease. In comparison with the dynamic modality, that requires increased radiation, precise acquisition protocols and dedicated post-processing softwares, static CT perfusion was associated with less radiation exposure, non-inferior diagnostic accuracy, easier interpretation of images and is nowadays more widely available.     

Myocardial perfusion and perfusion reserve in endurance-trained men

PURPOSE: This study was undertaken to determine whether endurance training is associated with changes in myocardial perfusion in humans. METHODS: Myocardial perfusion was measured in eleven trained and nine sedentary men at rest and during adenosine-stimulated hyperemia using positron emission tomography (PET). Left ventricular (LV) dimensions and mass were measured using echocardiography. Myocardial work per gram of tissue was calculated as (cardiac output. mean arterial blood pressure)/LV mass. RESULTS: LV mass was significantly higher and myocardial work per gram of tissue lower in the trained than in the untrained subjects. Basal (0.78 +/- 0.10 and 0.76 +/- 0.15 mL. min-1. g-1, P = NS) and adenosine-stimulated perfusion (3.46 +/- 0.91 and 3.14 +/- 0.70 mL. min-1. g-1, P = NS) were similar between trained and untrained men, respectively. Consequently, myocardial perfusion reserve was similar in both groups (4.4 +/- 1.2 and 4.1 +/- 0.7, P = NS). In addition, coronary resistance at baseline (115 +/- 17 vs 119 +/- 22, mm Hg. mL. min-1. g-1, P = NS) and during adenosine infusion (28 +/- 8 vs 30 +/- 8, mm Hg. mL. min-1. g-1, P = NS) were similar in both groups. Resting myocardial work correlated with resting myocardial perfusion in both groups, but the relationship between perfusion and work was different between the groups so that perfusion for a given myocardial work was significantly higher in trained subjects (0.56 +/- 0.04 and 0.34 +/- 0.05 mL. (mm Hg. L)-1, P < 0.001). CONCLUSIONS: These findings suggest that endurance trained subjects do not have different resting or adenosine-stimulated myocardial perfusion. However, the relationship between myocardial perfusion and work appears altered in the athletes.     

Myocardial perfusion

Noninvasive cardiac magnetic resonance (CMR) imaging has progressed rapidly over the past few years and will most likely become an integral part of the diagnostic workup of patients with known or suspected coronary artery disease (CAD). In this article the rationale for using perfusion-CMR is discussed, followed by a summary of current state-of-the-art perfusion-CMR techniques that addresses pharmacological stress, monitoring, pulse sequences, and doses of contrast media (CM) for first-pass studies. In the second part, unresolved aspects of perfusion-CMR, such as the lack of fully established and validated imaging protocols, are discussed. The optimum pulse sequence parameters, required cardiac coverage, analysis algorithms, criteria for data quality, and other aspects remain to be defined. Furthermore, since expertise in perfusion-CMR is not yet widely available, training of physicians and technicians to perform perfusion-CMR according to recognized standards is an important future requirement. In the last part of the review, some ideas are proposed to improve the management of patients with known or suspected CAD. This involves making a shift from a "reactive" strategy, in which patients are typically approached when they are symptomatic, to an "active" strategy, in which perfusion-CMR is performed for early detection of high-risk patients so that revascularizations can be performed before potentially deadly infarcts occur. An ideal test for such an active strategy would be highly accurate, reliable, safe (and thus repeatable), and affordable. Large multicenter trials have shown that in experienced centers perfusion-CMR is reliable and repeatable, and it is hoped that future studies will demonstrate its cost-effectiveness as well.     

Hepatic perfusion during hepatic artery infusion chemotherapy: evaluation with perfusion CT and perfusion scintigraphy

The standard method for the evaluation of hepatic perfusion during hepatic artery infusion (HAI) chemotherapy is planar hepatic artery perfusion scintigraphy (HAPS). Planar HAPS was performed with 2 mCi of [99mTc] macroaggregated albumin infused at 1 ml/min and compared with single photon emission CT (SPECT) HAPS and with a new study, CT performed during the slow injection of contrast material through the HAI catheter (HAI-CT). Thirteen patients underwent 16 HAI-CT studies, 14 planar HAPS studies, and 9 SPECT HAPS studies. In 13 of 14 studies (93%) HAI-CT and planar HAPS were in complete agreement as to the perfusion pattern of intrahepatic metastases and normal liver. In nine studies where all modalities were performed, the findings identified by HAI-CT and planar HAPS agreed in all cases, whereas the results of two SPECT scans disagreed with the other studies. With respect to perfusion of individual metastases, 14 of 14 HAI-CT studies, 12 of 13 planar HAPS studies, and 9 of 9 SPECT HAPS studies correctly demonstrated the perfusion status of individual lesions as indicated by the pattern of changes in tumor size determined on CT obtained before and after the perfusion studies. Hepatic artery infusion CT was superior for delineation of individual metastases, particularly small lesions, and for the evaluation of nonperfused portions of the liver. Planar HAPS detected extrahepatic perfusion in four patients, and this was not detected by HAI-CT. We conclude that HAI-CT and scintigraphy are complementary techniques. Hepatic artery infusion CT has advantages for the evaluation of intrahepatic perfusion, and planar HAPS is superior to HAI-CT for the detection of extrahepatic perfusion.     

Quantitative pixelwise myocardial perfusion maps from first-pass perfusion MRI

Objective:

To calculate and evaluate absolute quantitative myocardial perfusion maps from rest first-pass perfusion MRI.

Methods:

10 patients after revascularization of myocardial infarction underwent cardiac rest first-pass perfusion MRI. Additionally, perfusion examinations were performed in 12 healthy volunteers. Quantitative myocardial perfusion maps were calculated by using a deconvolution technique, and results were compared were the findings of a sector-based quantification.

Results:

Maps were typically calculated within 3 min per slice. For the volunteers, myocardial blood flow values of the maps were 0.51 ± 0.16 ml g⁻¹ per minute, whereas sector-based evaluation delivered 0.52 ± 0.15 ml g⁻¹ per minute. A t-test revealed no statistical difference between the two sets of values. For the patients, all perfusion defects visually detected in the dynamic perfusion series could be correctly reproduced in the maps.

Conclusion:

Calculation of quantitative perfusion maps from myocardial perfusion MRI examinations is feasible. The absolute quantitative maps provide additional information on the transmurality of perfusion defects compared with the visual evaluation of the perfusion series and offer a convenient way to present perfusion MRI findings.

Advances in knowledge:

Voxelwise analysis of myocardial perfusion helps clinicians to assess the degree of tissue damage, and the resulting maps are a good tool to present findings to patients.MRI is widely used for the evaluation of myocardial perfusion. Advantages of perfusion MRI are a higher spatial resolution compared with positron emission tomography (PET)^1,2 and single photon emission CT³ and the lack of exposure to radiation. Great efforts have been made to use MRI for quantitative evaluation of myocardial perfusion in the past years.^4,5 In clinical routine, however, evaluation of MRI perfusion examinations is performed by the visual analysis of the acquired images depicting areas remaining hypo-intense during the passage of the contrast agent bolus. One main reason for not quantifying myocardial perfusion is the sometimes-excessive user interaction time required for manual segmentation of the acquired images in the quantification process.If myocardial perfusion is quantified, in most studies, the high spatial resolution of the acquired MR images is not maintained. Instead, a sector-based evaluation is performed.^6,7 First attempts have been made to calculate myocardial perfusion maps to evaluate regional myocardial perfusion.^3,8–10 However, until now, these studies were performed in animals^8–10 or perfusion was only evaluated semiquantitatively.³ Recently, our group has published an automatic post-processing tool for quantitative perfusion evaluation.¹¹ That study focused on the automation of post-processing but confined itself on sectors of the myocardium. The next and consequent step is to evolve this technique to work on a pixel-by-pixel basis. Therefore, it was the goal of this study to develop and test a method that calculates pixelwise quantitative perfusion maps from myocardial perfusion MRI examinations. These maps might help the clinician in making a diagnosis by decreasing the number of images to be examined, because a pixelwise quantitative perfusion map demonstrates the information of a whole series of images obtained in a first-pass perfusion examination clearly arranged.     

Dipyridamole perfusion scintigraphy

Dipyridamole is one of several agents that may be infused intravenously to nonivasively evaluate coronary perfusion without dynamic exercise. Among such agents it is the most investigated, and it is associated with the greatest clinical experience. Its mechanism of action utilizes intrinsic adenosine and does not require the induction of ischemia. Rather, the method tests the coronary flow reserve by dilating the precapillary and arteriolar capillary beds. Vessels with a limited coronary flow reserve demonstrate reduced responsiveness with relative flow reduction and a resultant defect on perfusion scintigraphy. Side effects are common and generally benign, but deaths have been reported and they generally relate to severe hypotension, prolonged dense ischemia and resultant infarction, or bronchospasm. Severe complications are rare and can be avoided by the prompt administration of aminophylline, the dipyridample antedote. Diagnostic accuracy for the identification of coronary disease appears similar to that for exercise perfusion scintigraphy. It should be applied to patients with known or suspected coronary disease who require coronary evaluation, but who cannot exercise adequately for diagnostic or prognostic purposes. In such patients, the method is useful for the preoperative assessment of risk at peripheral vascular and other major noncardiac surgery. It may be of value as well in the assessment of the otherwise uncomplicated patient postinfarction. Not yet established is its application to the patient with unstable angina or in the acute setting, after coronary reperfusion. Similarly, its comparison with direct adenosine infusion or with pharmacological agents whose mechanism rests entirely on ischemia induction, as does dobutamine, has until now been limited. Unlike its use with perfusion scintigraphy, the application of dipyridamole with echocardiography and other functional ischemic indicators is totally dependent on the induction of ischemia. This is likely less frequent than the induction of nonischemic perfusion heterogeneity. The agent is now commonly available and will make a significant beneficial impact on patient evaluation and management.     

Myocardial kinetics of radiolabeled perfusion agents: Basis for perfusion imaging

The myocardial deposition of radiolabeled perfusion agents permits the noninvasive assessment of regional coronary blood flow. The design of imaging protocols and the optimal interpretation of clinical perfusion studies are based on an understanding of the kinetics of blood-tissue exchange for these compounds. Thallium 201 and the technetium 99m-labeled compounds sestamibi, teboroxime, and tetrofosmin show differing myocardial extraction and retention. This review focuses on studies that used cell culture, isolated heart, and intact animal models that form the basis of our current understanding of the myocardial kinetics of these imaging agents.     

Evolution of pulmonary perfusion defects demonstrated with contrast-enhanced dynamic MR perfusion imaging

Pulmonary perfusion defects can be demonstrated with contrast-enhanced dynamic MR perfusion imaging. We present the case of a patient with a pulmonary artery sarcoma who presented with a post-operative pulmonary embolus and was followed in the post-operative period with dynamic contrast-enhanced MR perfusion imaging. This technique allows rapid imaging of the first passage of contrast material through the lung after bolus injection in a peripheral vein. To our knowledge, this case report is the first to describe the use of this MR technique in showing the evolution of peripheral pulmonary perfusion defects associated with pulmonary emboli. Received: 27 July 1998; Revision received: 28 October 1998; Accepted: 20 January 1999