Author + information
- ↵*Reprint requests and correspondence:
Dr. Scott D. Flamm, Cardiovascular Imaging, Mail Code J1-4, Cleveland Clinic, 9500 Euclid Avenue, Cleveland, Ohio 44195
There is only one way in which a person acquires a new idea; by combination or association of two or more ideas he already has into a new juxtaposition in such a manner as to discover a relationship among them of which he was not previously aware.
—Francis A. Carter (1)
According to the American Heart Association, at least 81,100,000 (1 in 3) American adults have some form of cardiovascular disease; approximately 17,600,000 have coronary artery disease, and nearly 6,000,000 have congestive cardiac failure (2). Assessment of myocardial viability in these patients has recently been revolutionized by the introduction of delayed enhancement (DE) cardiac magnetic resonance (CMR). This simple, reproducible, noninvasive imaging technique yields images with high spatial and contrast resolution, permitting physicians to distinguish between myocardial scar/fibrosis and normal myocardium without exposing patients to iodinated contrast agents or ionizing radiation (3).
The importance of myocardial viability assessment relative to the success of coronary revascularization has been well documented (3,4). Furthermore, investigators have shown that the presence of myocardial scarring, as detected by CMR or gated single-photon emission computed tomography in preferred areas of lead placement, could result in unresponsiveness to resynchronization therapy (5,6).
The literature contains a number of reports regarding the fusion of images and datasets obtained from different imaging modalities: positron emission tomography and multislice computed tomography (CT) in the evaluation of coronary artery disease (7); 3-dimensional (3D) electroanatomic mapping and either contrast-enhanced magnetic resonance angiography (MRA) or contrast-enhanced CT of the left atrial and pulmonary venous system (8); and multislice CT and perfusion CMR in the evaluation of the functional significance of coronary stenosis (9). Fusion of such data is intended to bring out the best of both modalities, offering clinicians complementary perspectives, along with better spatial orientation, without the need to juggle 2 different datasets.
In this issue of iJACC, White et al. (10) describe the clinical application of a fusion technique that efficiently uses not 2 modalities but only a single one. The investigators describe the use of 3-T CMR to obtain 3D isotropic DE-CMR and 3D whole-heart MRA images for assessing myocardial scar and coronary arteries and veins, using a slow infusion of gadolinium chelate, in patients undergoing revascularization or cardiac resynchronization therapy. In combining the DE-CMR dataset (in which 44 of 49 studies showed myocardial scar) and the MRA dataset by using open source software, the investigators had an 86% success rate (38 studies); in the failed fusion studies, lack of success was a result of the limited quality of the DE-CMR data. The investigators acknowledged that the study was not designed to assess the accuracy of whole-heart MRA versus invasive angiography (the gold standard), particularly because the spatial resolution of whole-heart MRA was limited to 1.3 × 1.3 × 1.3 cm3. Instead, they used this opportunity to investigate the clinical significance of their findings. Interestingly, the fusion technique was described as having a moderate impact on the management of two-thirds of the cases (although the exact clinical details were not provided). On the basis of the results, nearly 20% of the scheduled revascularization and resynchronization procedures were canceled.
In patients undergoing resynchronization therapy, the posterolateral cardiac vein is the most common site for left ventricular (LV) lead placement, but placing the LV lead in the site with the latest activation could yield a better response (11). The ability to identify the location and degree of myocardial scar in relationship to the available coronary veins is potentially important to electrophysiologists in selecting the optimal location for LV lead placement. Complicating this selection is the known variability of the coronary venous system anatomy (12,13); therefore, the ability to clarify the anatomy and provide a “road map” before lead implantation is increasingly critical to electrophysiologists.
The use of isotropic 3D DE-CMR is attractive because this technique provides a high signal-to-noise ratio, and the dataset can be evaluated interactively by means of advanced 3D-imaging workstations. However, the mean imaging time for the 3D sequence described by White et al. (10) was at least 6 min. During this period, the inversion time necessary to achieve satisfactory myocardial “nulling” typically increases; this alteration may well have contributed to the fact that a number of White et al.'s studies were not evaluable owing to an inappropriate inversion time. The investigators did not provide details regarding the precise DE-CMR sequence used in this study; a commercially available 3D navigator phase-sensitive inversion-recovery sequence potentially could have minimized the variation in the inversion time related to the prolonged imaging time. In contrast to the coronary venous anatomy, the coronary arterial anatomy is fairly constant. Therefore, given the prolonged imaging time (often ≥15 min) and additional programming time necessary for fusion of coronary anatomic and DE-CMR images, a comparison study is needed to determine whether the fusion technique will provide more useful information for clinicians than a high-quality DE-CMR dataset alone, which generally takes a substantially shorter time to acquire.
Regarding the coronary veins, the investigators reported a high quality score (average ≥3, indicating good or excellent quality) in this study. The coronary sinus is relatively large in caliber and therefore could be imaged without undue difficulty; however, the commonly used posterolateral coronary vein is much smaller (particularly in women) (12), and a higher spatial resolution than that used in this study may be necessary for adequate visualization of the coronary venous anatomy. As the investigators suggested, the use of newer imaging coils and newer intravascular contrast agents could help improve the image quality without significantly prolonging the imaging time. Reducing the imaging time is important when using navigator-guided sequences, to minimize the potential for motion artifacts in these patients, who often have serious cardiovascular comorbidities.
In summary, this study by White et al. (10) is important because it shows the feasibility of matched, isotropic 3D imaging of coronary vasculature (albeit at a modest spatial resolution) and myocardial scar using a single imaging modality, unlike previously described methods that use different imaging modalities. This fusion technique provides physicians with a “visual road map” of the potential target arteries and veins, allowing more direct evaluation of significant nonviable myocardial areas fed by coronary arteries (in potential candidates for revascularization) or drained by coronary veins (in candidates for cardiac resynchronization therapy). Fused whole-heart coronary and myocardial scar imaging may prove increasingly valuable in determining the success of these procedures. Instead of simply blending pretty images, it potentially offers another means of relieving symptoms and improving patient survival.
We are grateful for the editorial assistance of Virginia C. Fairchild of the Section of Scientific Publications, Texas Heart Institute at St. Luke's Episcopal Hospital, Houston, Texas.
The authors have reported that they have no relationships to disclose.
↵* Editorials published in JACC: Cardiovascular Imaging reflect the views of the authors and do not necessarily represent the views of JACC: Cardiovascular Imaging or the American College of Cardiology.
- American College of Cardiology Foundation
- Johnson L.A.
- ↵Heart Disease and Stroke Statistics: 2010 Update At-A-Glance. http://www.americanheart.org/downloadable/heart/1265665152970DS-3241%20HeartStrokeUpdate_2010.pdf. Accessed May 21, 2010.
- Allman K.C.,
- Shaw L.J.,
- Hachamovitch R.,
- Udelson J.E.
- Bleeker G.B.,
- Kaandorp T.A.,
- Lamb H.J.,
- et al.
- Ypenburg C.,
- Schalij M.J.,
- Bleeker G.B.,
- et al.
- Namdar M.,
- Hany T.F.,
- Koepfli P.,
- et al.
- ↵Stolzmann P, Alkadhi H, Scheffel H, et al. Image fusion of coronary CT angiography and cardiac perfusion MRI: a pilot study. Eur Radiol;20:1174–9.
- White J.A.,
- Fine N.,
- Gula L.J.,
- et al.
- Ypenburg C.,
- van Bommel R.J.,
- Delgado V.,
- et al.