Ischemic heart disease: value of MR techniques

Background. The cardiovascular applications of magnetic resonance (MR) techniques in coronary artery disease have increased considerably in recent years. Technical advantages of MR imaging are the excellent spatial resolution, the characterization of myocardial tissue, and the potential for three-dimensional imaging. These characteristics allow the accurate assessment of left ventricular mass and volume, the differentiation of infarcted from normal tissue, and the determination of systolic wall thickening and regional wall motion abnormalities. Methods. In addition to the conventionally used spin-echo and cine-echo techniques, newer techniques such as myocardial tagging, ultrafast MR imaging and MR coronary angiography have been developed. These newer techniques allow a more accurate assessment of ventricular function (tagging), myocardial perfusion (ultrafast imaging), and evaluation of stenosis severity (MR coronary angiography). Particularly early detection and flow assessment of stenosed coronary arteries and bypasses by MR angiography would constitute a major breakthrough in cardiovascular MR imaging. Apart from the MR imaging techniques, cardiac metabolism may be well assessed using MR spectroscopy. This provides unique information on the metabolic behaviour of the myocardium under conditions stress-induced ischemia. However, the definite niche of cardiac MR spectroscopy has still to be settled. Conclusion. Currently, MR techniques allow the evaluation of anatomy and function (accepted use), perfusion and viability (development phase), and coronary angiography (experimental phase). A particular strength of MR imaging is that one single MR test may encompass cardiac anatomy, perfusion, function, metabolism and coronary angiography. The replacement of multiple diagnostic tests with one MR test may have major effects on cardiovascular healthcare economics and would outweigh the cost inherent to the MR angiography procedure.     

Assessment of coronary artery bypass graft patency by multidetector computed tomography and electron-beam tomography

This case report describes the use of retrospectively ECG-gated 16-slice multidetector computed tomography (MDCT) and electron-beam tomography (EBT) for assessing bypass graft patency in two patients with recurrent angina after coronary artery bypass graft surgery. The results of each tomographic modality were compared to the findings of traditional coronary angiography. In the first patient MDCT showed occlusion of the left internal mammary artery (LIMA) and saphenous vein graft after the second anastomosis. Coronary angiography confirmed these findings. In the second patient EBT showed patency of the LIMA and saphenous vein graft. After the first anastomosis of the saphenous vein graft, the connected vessel filled poorly. Coronary angiography confirmed both grafts to be patent, and detected an occlusion distal to the first anastomosis. These findings support the evidence that both MDCT and EBT are suitable techniques for establishing bypass graft patency by non-invasive means.     

MRI检测活性心肌及其与冠状动脉造影、SPECT和PET对比研究

目的：分析MRI对冠心病患者心肌活性的诊断价值并与冠状动脉造影、SPECT和PET结果对比。方法：应用MRI对21例临床符合冠心病的患者进行检查，并将结果与冠状动脉造影、SPECT和PET检查结果对照。结果：MRI静息心肌灌注扫描检出的缺血节段比狭窄冠状动脉的供血节段少但无统计学差异（Z=-1.732，P=0．083）；比SPECT心肌灌注扫描检出的缺血节段多且有统计学差异（Z=-3．691，P=0．000）。SPECT心肌灌注扫描检出的缺血节段比狭窄冠状动脉的供血节段少且有统计学差异（Z=-3．029，P=0．002）。以正电子发射断层显像（PET）结果为标准，MR延迟扫描检测活性心肌的灵敏度为97．6％，特异度为98．4％，总符合率为98．2%，Kappa值为0．953。MR延迟扫描检出的活性心肌比PET检出的少但无统计学差异（Z=-0．209，P=0．835）。结论：MR心脏检查清晰显示心肌梗死的位置、程度和附壁血栓情况，并可对左室室壁运动进行直观显示。常规SPECT心肌灌注显像由于空间分辨率低明显低估心肌缺血范围。心肌PET显像空间分辨率低，无法显示心肌梗死的透壁程度，且不能直观显示室壁运动情况。     

Non-invasive analysis of myoblast transplants in rodent cardiac muscle

Background: Magnetic resonance imaging (MRI) of magnetically labeled stem cells is a non-invasive approach that can provide images with high spatial resolution. We evaluated the ability of a commercially available, Food and Drug Administration (FDA) approved contrast agent to allow the monitoring of myoblast transplants in the rodent heart. Methods and Results: Primary rat myoblasts were efficiently labeled by incubation with ferumoxide–polycation complexes and labeled cells retained their normal capacity to generate mature myotubes. Intra-cellular iron-oxide accumulation resulted in MRI contrast changes, allowing for three-dimensional, non-invasive detection of labeled cells in the rodent myocardium. Histological analysis of hearts injected with labeled myoblasts or control, non-viable myoblasts revealed that areas of MRI contrast changes corresponded to iron contained within engrafted myotubes and scavenger cells up to two months post-injection. Conclusions: The high sensitivity of MR imaging will allow for non-invasive studies of cardiac stem cell migration and homing. Additional techniques are in development to non-invasively determine stem cell engraftment rates, viability and differentiation.     

Magnetic resonance imaging of coronary artery occlusions in the navigator technique

Non-invasive assessment of coronary arteries is possible with magnetic resonance imaging (MRI). Respiratory gated MR coronary angiography is a new imaging technique that permits reconstruction of the coronary arteries based on a three-dimensional (3D) data set obtained from the free-breathing patient. In this study, respiratory gated MR angiography (MRA) was performed to assess coronary artery occlusions. MRI was performed in 25 patients who had been referred for conventional coronary angiography because of suspected coronary artery disease. Coronary artery occlusion was evaluated in the proximal and middle vessel segments after multiplanar coronary reconstruction of the MR images. Five patients were excluded from the study; in the remaining 20 patients 120 coronary artery segments were analyzed. Good image quality could be obtained for 85% of the segments. Eighteen of the 24 occlusions were confirmed by MRI, the overall sensitivity was 75% and the specificity was 100%. The best results were found in the proximal left anterior descending (LAD) and descending parts of the right coronary artery (RCA), where all occlusions were confirmed. These results showed that coronary artery occlusions can be detected in the proximal and middle LAD and RCA using 3D respiratory gated MRA. Further technical improvements, especially in spatial resolution, are necessary before MRA can become a reliable diagnostic tool in the non-invasive evaluation of coronary arteries.     

Nonangiographic assessment of coronary artery bypass graft patency

Coronary artery bypass graft patency can be assessed using the indirect techniques of evaluating patients' symptoms and exercise tolerance, changes in stress electrocardiogram, radioisotope regional perfusion, and myocardial wall contraction. The direct techniques assess graft patency directly by visualizing grafts using conventional computed tomography (CT), ultrafast CT, magnetic resonance imaging, digital subtraction angiography, and echocardiography. The advantages and disadvantages of each of these modalities are reviewed. At the present time, ultrafast CT and possibly magnetic resonance imaging and Doppler appear to be the only techniques besides angiography that can consistently evaluate bypass graft patency. Although they have the advantage of being minimally invasive, they cannot show graft stenosis or sequential graft patency. These techniques are best used in following patients after coronary bypass graft surgery and ruling out graft closure as the source of chest pain.     

Magnetic-resonance velocity mapping of the central circulation

Summary. In magnetic-resonance (MR) velocity mapping there exists a linear relationship between the velocity and signal in each element of a tomographic image. The technique can be used for quantitative measurements of linear velocities (m s^_1) and flow rates (1 min^-1). By using cinematographic images the flow profile during the cardiac cycle can be determined. This allows quantification of forward flow, regurgitant volume and regurgitant fraction in cases of heart-valve insufficiency. In valvular stenosis the transvalvular pressure gradient and valve area can be determined. Magnetic-resonance velocity mapping may also provide information about diastolic function of left ventricular function. Together with other MR imaging techniques, velocity mapping gives an accurate assessment of the severity of aortic dissection. Recent studies indicate that MR velocity mapping provides quantification of renal blood flow, and that MR imaging may be used even for coronary angiography and measurements of coronary blood flow. Therefore MR velocity mapping has the potential to become an important clinical tool for examination of the cardiovascular system providing high accuracy and quantitative measurements.     

Non-invasive assessment of graft patency using transcutaneous Doppler echocardiography for the validation of functional improvement after PTCA of the LAD via internal thoracic artery graft

Percutaneous transluminal coronary angioplasty (PTCA) of a native coronary artery via internal thoracic artery (ITA) graft after bypass surgery is a relatively rare procedure. Our current study evaluates the flow velocity patterns of the graft before and after PTCA. After intervention the mean diastolic flow velocity increased under rest and stress conditions. In addition, the graft patency was proved not before control angiography after 6 months. It could be verified that the measurement of flow velocity patterns under rest and stress conditions is a useful non-invasive procedure for monitoring long-term patency and PTCA-results of this vessel.     

MRI of myocardial perfusion.

An overwhelming number of myocardial perfusion studies are done by nuclear isotope imaging. Magnetic resonance imaging during the first pass of an injected, contrast bolus has some significant advantages for detection of blood flow deficits, namely higher spatial resolution, absence of ionizing radiation, and speed of the test. Previous clinical studies have demonstrated that excellent sensitivity and specificity can be achieved with MR myocardial perfusion imaging for detecting coronary artery disease, and assessment of patients with acute chest pain. Furthermore, an absolute quantification of myocardial blood flow is feasible, as was demonstrated by comparison of MR perfusion imaging, to measurements with isotope labeled microspheres in experimental models. An integrated assessment of perfusion, function, and viability, is thus feasible by MRI to answer important clinical challenges such as the identification of stunned or hibernating, but viable myocardium.     

Imaging Techniques in Nuclear Cardiology for the Assessment of Myocardial Viability

The assessment of myocardial viability has become an important aspect of the diagnostic and prognostic work-up of patients with ischemic cardiomyopathy. Although revascularization may be considered in patients with sufficient viable myocardium, patients with predominantly scar tissue should be treated medically. Patients with left ventricular dysfunction who have viable myocardium are the patients at highest risk because of the potential for ischemia but at the same time benefit most from revascularization. It is important to identify viable myocardium in these patients, and radionuclide myocardial scintigraphy is an excellent tool for this. Single-photon emission computed tomography perfusion scintigraphy (SPECT), whether using ²⁰¹thallium, ^99mTc-sestamibi, or ^99mTc-tetrofosmin, in stress and/or rest protocols, has consistently been shown to be an effective modality for identifying myocardial viability and guiding appropriate management. Metabolic and perfusion imaging with positron emission tomography (PET) radiotracers frequently adds additional information and is a powerful tool for predicting which patients will have an improved outcome from revascularization. New techniques in the nuclear cardiology field, like attenuation corrected SPECT, dual isotope simultaneous acquisition (DISA) SPECT and gated FDG PET are promising and will further improve the detection of myocardial viability. Also the combination of multislice computed tomography scanners with PET opens possibilities of adding coronary calcium scoring and non-invasive coronary angiography to myocardial perfusion imaging and quantification. Evaluation of the clinical role of these creative new possibilities warrants investigation.     

冠状动脉桥血管的多层螺旋CT和造影评价

目的:评价多层螺旋CT在显示冠状动脉桥血管中的临床应用价值。方法:21例冠状动脉血管旁路移植术后患者行多层螺旋CT血管成像及常规造影检查,分析CT诊断桥血管通畅性和狭窄的可靠性。结果:多层螺旋CT血管成像成功检测出21例患者共45支桥血管,15支桥血管闭塞,30支桥血管通畅,10支共16处狭窄,5支桥血管明显狭窄(>50%)8处,5支桥血管显示轻度狭窄(<50%)病变8处,MSCT评价桥血管闭塞和明显狭窄和导管造影完全符合。结论:多层螺旋CT尤其是64层CT能够准确地评价冠状动脉桥血管及吻合口的通畅性和狭窄情况,可以作为临床上对冠状动脉桥血管可疑病变的一种常规的无创性检查手段。     

Evaluating the function of aortocoronary bypasses with magnetic resonance tomography

Following an aortocoronary bypass operation the differential diagnosis of chest pain of recent onset may be difficult (ischaemia, thoracotomy induced pain). At this point noninvasive methods are preferable to angiography in order to reach exact diagnosis. Magnetic Resonance Imaging (MRI), a new noninvasive imaging method, makes it possible to get anatomical and blood flow information without the use of ionizing radiation or contrast agents. It was the aim of our study to examine the diagnostic impact of MRI for the assessment of aortocoronary bypass graft patency. We compared three different acquisition techniques (a spinecho sequence and two fast-gradient echo sequences). 26 patients were examined, 49 bypass grafts were eligible for comparative evaluation. As compared with the spinecho technique, fast echo gradient sequences had a higher sensitivity (FISP 93%, FLASH 88%) than the spinecho technique 79%, and a higher accuracy (FISP 88%, FLASH 82%) versus 73%, respectively. We conclude that MRI may have a high diagnostic potential in the evaluation of early postoperative aortocoronary bypass graft patency.     

Composite arterial grafting

The success of coronary artery bypass grafting, the gold standard for the treatment of multivessel coronary artery disease, is limited by poor long-term vein-graft patency. By contrast, the left internal mammary artery has been demonstrated to have a superior graft patency rate and has provided excellent clinical results. This suggests that the use of arterial conduits for coronary artery bypass grafting may be beneficial for long-term results. Recently, there has been an upsurge in the use of arterial grafts for myocardial revascularization based on the clinical advantage of the use of the left internal mammary artery as a bypass conduit. Many retrospective studies have supported the safety and the effectiveness of arterial grafting, and it has become apparent that the free arterial graft can be used as a branched or a lengthened conduit to the in situ arterial graft by adopting one or more of the several composite grafting techniques. Arterial composite grafts with or without sequential grafting techniques appear an attractive strategy as increased number of distal coronary anastomoses can be performed, with a limited number of grafts, avoiding proximal aortic anastomoses. However, concerns regarding the total dependence of the coronary bypass flow on the flow of one in situ arterial graft and technical error, resulting in compromised flow in one or both limbs of the composite graft have prevented composite arterial grafting from being universally adopted. It is expected that in the near future a prospective, multi-institutional, randomized controlled trial, to compare the short- and long-term outcomes of exclusive arterial grafting using composite and conventional aortocoronary revascularization strategies, will be undertaken to validate the safety and efficacy of composite arterial grafting.     

Molecular MRI of Atherosclerosis Burden

Atherosclerosis is a systemic vascular disease predominantly affecting the intima of central and peripheral arteries. Its complications, myocardial infarction and stroke, remain the leading cause of morbidity and mortality in the Western world and developing countries. Angiographic imaging methods are the current gold standard for the clinical graduation of coronary and carotid artery disease and the guidance of treatment. These techniques are however limited to the assessment of the extent of luminal narrowing. MRI is a noninvasive modality, which allows the direct evaluation of the thin arterial vessel wall with excellent soft tissue contrast and high spatial resolution. Targeted MR contrast agents enable the evaluation of specific cellular and subcellular markers on a molecular level. This review will introduce and discuss novel molecular MR imaging techniques for the assessment of plaque and inflammatory burden in the context of atherosclerosis. Both measures can provide additional information beyond the assessment of luminal stenosis alone.     

MRI of coronary arteries

Magnetic Resonance Angiography (MRA) of the coronary arteries has recently become possible due to the development of a new group of ultrafast imaging sequences. Although the role of coronary MR angiography in screening for coronary artery lesions has not yet been established, coronary MR angiography has been very successful in the detection of coronary artery variants, and the imaging of coronary stents and bypass grafts. Variants of these new MRI techniques can also quantitate velocity in native coronary arteries. Coronary MR angiographic techniques can be subdivided in breath-hold (single or repeated breath-hold) and non-breath-hold techniques. Most of the clinical experience so far has been with a single breath-hold technique, and was limited to cooperative patients. The recent introduction of navigator pulses for real-time respiratory gating or triggering allows non-breath-hold or repeated breath-hold 3–D coronary MR angiography, and will allow a more widespread use of this technique. Notwithstanding the progress being made and the excitement created by the prospect of a noninvasive coronary artery screening tool, several key technical problems remain unresolved and are now being addressed by the scientific and clinical community. This paper reviews ongoing research in coronary MR angiography.     

Advanced cardiovascular imaging in congenital heart disease

In recent years, there has been increased utilisation of advanced cardiovascular imaging modalities for congenital heart disease (CHD) because of increased survival rates from improved surgical and interventional techniques and medical care. Cardiovascular magnetic resonance imaging (MRI) in particular has seen increased clinical and research utility. The non-invasive nature of cardiovascular MRI, its lack of radiation exposure, versatility and reproducibility make it the modality of choice for patients with poor echocardiographic windows and patients who need further evaluation of pre- and postoperative CHD. Cardiovascular MRI is also the gold standard for the assessment of right ventricle (RV) volumes and function. Computed tomography (CT) is useful for demonstration of anatomy and less useful for assessment of cardiac function. Although concerns have been raised about radiation safety, dose-reduction techniques are available.     

Current results and new developments of coronary angiography with use of contrast-enhanced computed tomography of the heart.

Electron beam computed tomography (EBCT) is the reference standard for x-ray-based tomographic imaging of the heart because of its high temporal resolution, but it is available in only a few centers. Quantification of coronary calcium is the most widely recognized use of EBCT for cardiac imaging. This technique requires no contrast media and provides an accurate assessment of overall plaque burden in the coronary tree; however, it does not directly identify or localize coronary stenoses. Multislice spiral (helical) CT (MSCT) is a new technology that provides images of the beating heart in diagnostic quality under many circumstances and may facilitate the broader application of cardiac and coronary CT. Currently, for imaging of the heart, much more experience exists with EBCT than with MSCT. Contrast-enhanced CT coronary angiography (CTCA) can be done with EBCT or MSCT to obtain images of the major branches of the coronary tree and to define luminal narrowing. Studies at experienced centers performed with small numbers of patients show that sensitivity, specificity, and negative predictive value are good with CTCA in the assessment of obstructive coronary artery disease, but CTCA remains an investigational technique for these applications. Computed tomographic coronary angiography can be clinically useful for assessing coronary artery bypass graft patency and congenital coronary abnormalities.     

Congenital cholesteatoma and cholesterol granuloma of the temporal bone: role of magnetic resonance imaging

Magnetic resonance imaging (MRI) can be of significant benefit in characterizing expansile lesions of the petrous apex. MRI can be of particular help in distinguishing congenital cholesteatoma from cholesterol granuloma. Furthermore, with the advent of faster high-resolution scanning techniques, MRI can define precise spatial relationships of these masses with the middle and inner ear structures, internal carotid artery, jugular vein, and other structures of the skull base. MRI scanning is sensitive in detecting intracranial extension of these masses. MR angiography can provide additional information regarding the relationship of these masses with adjacent vascular structures and confirm patency of the adjacent vessels. In the postoperative period, MR scanning can help evaluate for complete removal, complication, recurrence, or formation of complicating granulation tissue.     

常规超声结合冠脉血流显像技术评价冠状动脉搭桥术后桥血管通畅性

目的应用常规超声结合冠脉血流显像技术评价冠状动脉搭桥术后桥血管通畅性.方法行冠状动脉搭桥术(左乳内动脉原位转流至左前降支)患者46例;术后检查乳内动脉桥起始段、桥血管远段(吻合口近端)、吻合口、远端及近端左前降支.分别测量各段收缩期峰值流速、舒张期峰值流速、收缩期流速时间积分、舒张期流速时间积分.结果乳内动脉原位转流术后, 桥血管起始段显示率95.65%;桥血管与自体左前降支吻合口显示率80.43%.通过测量并计算吻合口与吻合口近端桥血管流速时间积分比值以及舒张期峰值流速比值评价吻合口是否存在狭窄.结论常规超声结合冠脉血流显像技术可提供评价桥血管通畅性的直接证据,为临床随访提供一种新的无创的方法.     

MR imaging of ischemic heart disease

When ischemic heart disease (IHD) is suspected or confirmed, the primary imaging modality is echocardiography. When appropriate, complementary examinations can be performed. These include stress perfusion scintigraphy, cardiac catheterization, coronary angiography, and CT. MR imaging techniques have developed rapidly over the past several years, and MR imaging has the ability to delineate myocardial perfusion, ventricular function, and myocardial viability in a single examination. Although coronary MR angiography is promising, in recent years it has been supplanted as a noninvasive imaging modality by coronary CT angiography. The other capabilities of MR imaging suggest that it will be performed more and more frequently for the assessment of IHD.