MDCT evaluation of the cardiac venous system

Purpose

This study was undertaken to evaluate the usefulness of electrocardiographically (ECG)-gated multidetector-row computed tomography (MDCT) for the assessment of the coronary venous system and detection of its anatomical variants, in order to identify those suitable for lead placement in cardiac resynchronisation therapy (CRT).

Materials and methods

We retrospectively examined the coronary MDCT studies of 89 patients (73 males, 16 females, average age 62.5 years, range 31–79) referred for suspected coronary artery disease. The cardiac venous system was assessed in all patients using three-dimensional (3D) postprocessing on a dedicated Vitrea workstation (five patients were excluded from the analysis).

Results

The coronary sinus, the great cardiac vein, the anterior interventricular vein and the middle cardiac vein were visualised in all cases. The lateral cardiac vein was visualised in 56/84 patients (67%) and the posterior cardiac vein in 63/84 patients (75%), never both missing. Along the postero-lateral wall of the left ventricle, only one branch was present in 44 cases, two branches in 21 cases and three or more branches in 19/84 cases (22%). Evaluation of the maximum diameter revealed that the lateral vein was dominant over the posterior vein in 20/40 cases. The small cardiac vein was visualised in 11/84 cases.

Conclusions

MDCT provides good depiction of the cardiac venous system, enabling the study of the vessel course and the identification of anatomical variants. Hence, this imaging technique could be proposed for the preoperative planning of CRT in selected patients.     

Estimation of cardiac output by bioimpedance cardiography

Changes in thoracic electrical bioimpedance during the cardiac cycle have been related to the ejection of the stroke volume of blood during cardiac systole. Refinements in the recording and analysis of these changes permit estimation of cardiac output. Encouraging reports comparing results obtained by this method and those obtained simultaneously using the current standard invasive method have been published. While there are limitations, the advantages of this technique are sufficient to make bioimpedance cardiography attractive to the military physician. It is for these reasons that the principles of this technology are reviewed in this paper.     

Various findings of cardiac thrombi on MDCT and MRI

Cardiac thrombus accompanies risk for peripheral embolization, either into the systemic circulation (from the left heart) or into the pulmonary arteries (right heart). In fact, the presence of peripheral emboli should prompt the search for a source within the heart. Echocardiography is the present technique of choice. Also, computed tomography and magnetic resonance imaging may provide additional information. In this article, we will demonstrate various features of cardiac thrombus on computed tomography and magnetic resonance imaging such as mural thrombus after myocardial infarction, thrombus at left atrial appendage in patients with mitral stenosis, thrombus mimicking tumor, organized thrombus containing calcification at left atrium, and compact moderator band mimicking thrombus.     

Basics of cardiac MDCT: techniques and contrast application

The purpose of this article is to review the basic techniques of cardiac MDCT including the most recent 64-slice scanner generation. Besides the technical developments of different MDCT generations within recent years, the basic principles of ECG-related CT algorithms are discussed. Retrospective ECG-gated data acquisitions are considered as a prerequisite for reliable and reproducible calcium scoring as well as for volumetric assessment of the coronary artery tree. While data acquisition itself is rather straightforward, the optimization of image quality, the knowledge of adequate scan protocols and especially knowledge of possibly arising artefacts is mandatory for a stable high image quality. As data acquisition is becoming faster with the most recent advent of 64-slice MDCT, protocols have to be adapted to this new scanner generation. On the other hand, the improvement in spatial as well as in temporal resolution shows impact on the accuracy and stability of coronary CT angiography. However, the use of dose-reducing technical improvements is strongly recommended.     

Clinical usefulness of novel cardiac MDCT/SPECT fusion image

Background  We evaluated the relationship between computed tomography angiography (CTA) and SPECT, and assessed to determine the clinical usefulness of the fusion image using CTA and myocardial perfusion imaging (MPI). Methods  Forty-one consecutive patients [after coronary artery bypass operation (n = 13) and suspected stenosis (n = 28)] underwent MPI and CTA. SPECT/CTA fused images were generated. Results  In total, 687 segments including bypass graft in 164 coronary arteries were analyzed. Myocardial ischemia on MPI was observed in 11 patients among 28 with CTA abnormalities, one had both ischemia and infarction, and 7 had only infarction. Segment-based analysis showed that ischemia was found in 14 segments (24%) among 59 stenoses on CTA. Forty stenotic segments (69%) were not associated with perfusion abnormality. The rest 5 stenotic segments were considered equivocal (8%). A fusion image made it possible to associate perfusion defects with its corresponding coronary artery in 4 out of 5 equivocal lesions on side-by-side analysis. Patients with incremental diagnostic information on SPECT/CTA fusion (n = 4) had significant smaller coronary diameter than that of not-improved coronary vessels (2.0 ± 0.4 vs. 3.9 ± 0.4 mm, p = 0.001). Conclusion  Cardiac fusion imaging accurately diagnosed functionally relevant coronary stenosis. SPECT/CTA fusion images in coronary artery disease may provide added diagnostic information on functional relevance of coronary artery disease.     

Estimation of cardiac output by first-pass transit of radiotracers

To evaluate cardiac function with various tracers to be used for radionuclide scintigraphy, we examined the validity of a simplified method to measure cardiac output (CO) by modifying the equation of Stewart-Hamilton in the radionuclide study. After a bolus injection of I-123 or Tc-99m tracer, the total injection dose and count in the pulmonary artery during the first transit of the tracer were measured to calculate the CO Index. The CO Index was obtained from the integral of the first transit of radiotracers in the pulmonary artery divided by the total injected count. CO was estimated from the regression formula which was obtained by comparing the CO Index with CO measured by the Doppler echocardiographic method. There were close correlations between the CO Index and CO measured by Doppler echocardiography both in the study with I-123 (n = 13, r = 0.85, p < 0.001) and with Tc-99m (n = 17, r = 0.88, p < 0.001). The regression formula varied according to the radionuclide used for the study (CO = 2.29 x (CO Index)(0.634) for I-123 and CO = 3.18 x (CO Index)(0.518) for Tc-99m). CO measured by this method is useful for the assessment of cardiac function with various tracers in routine clinical studies, and this simple method may be utilized for assessment of organ blood flow on the basis of the microsphere model.     

Advances in vascular and cardiac MDCT imaging: peripheral arteries

When compared to a standard dose of a relatively lowconcentration contrast material, the use of a small volume of iomeprol 400 yielded higher arterial enhancement from the abdominal aorta down to the femoral arteries with minimal or no venous overlap and without significant differences in terms of diagnostic output.     

Should we screen MDCT patients for risk of CIN?

A small percentage of patients referred for imaging procedures involving administration of contrast media (CM) are at risk for contrast-induced nephrotoxicity (CIN), a complication that can be fatal. It is therefore important to identify those at greatest risk so that precautionary measures can be taken. However, routine screening to identify high-risk individuals is highly variable among institutions that perform computed tomography (CT), and many referring physicians are not fully aware of the risks associated with CM-enhanced imaging procedures. Assessment of the presence of risk factors (e. g. renal disease, diabetes, hypotension) can help identify patients at risk who warrant further investigation. Although measurement of serum creatinine (SCr) level is commonly used to estimate renal function, it is not an ideal marker. Because SCr depends on muscle mass and is not usually elevated until the glomerular filtration rate (GFR) has fallen by at least 50%, it can underestimate renal dysfunction, particularly in women and the elderly. In contrast, GFR is a more accurate measure of renal function in most patients. The value of using GFR to identify patients at risk of CIN has been demonstrated in a retrospective review of 561 patients undergoing CM-enhanced CT. This study found that SCr identified 11.8% of patients as being at risk for CIN, whereas GFR identified 24.8% of patients as being at risk. In conclusion, accurate assessment of patients at risk for CIN should be performed prior to administering CM and should probably involve calculation of GFR and SCr.     

Estimation of exposure dose on MDCT examination--the measurement of organ dose and effective dose by anthropomorphic phantom

In order to evaluate the exposure dose in CT examinations, we measured the tissue and organ doses by test site in 4-row, 16-row, and 64-row multi detector CT by using an anthropomorphic phantom and fluorescent glass dosimeters. Furthermore, we calculated the effective dose by using the tissue weighting factor recommended by the ICRP in 2007. The effective dose in the head and neck examinations was 1.4-3.1 mSv, whereas the maximum skin dose was 278.9 mGy in head perfusion CT. The effective dose in examinations of the body trunk was 10.1-35.2 mSv. In addition, the organ dose and skin dose in the scanning range was similar to the CTDI(vol) in head and neck examinations, while it was higher than the CTDI(vol) in examinations of the body trunk. The exposure dose of patients undergoing CT is high in comparison to other radiological examinations. As a result, due to consecutive examinations, an absorbed dose of more than 100 mGy is possible. A future problem therefore remains how to lower the overall exposure dose with the introduction of new radiographic diagnostic modalities, such as phase scan or coronary CT angiography.     

Estimation of the left ventricular diastolic function with cardiac MDCT: correlation of the slope of the time-enhancement-curve with the mitral annulus diastolic velocity

Patients with diastolic heart failure tend to have a poor outcome, similar to that for patients with systolic heart failure. The aim of this study was to explore the ability of MDCT to estimate the left ventricular diastolic function. Thirty patients with suspected coronary artery disease underwent MDCT and echocardiography. The early transmitral flow velocities (E) and the velocity of mitral annulus early diastolic motion (e') were measured in order to evaluate the diastolic function. The scanning delay of CT was determined using a test injection technique. The aortic enhancement was measured over the aortic-root lumen, and it was plotted over time to yield a time-enhancement-curve. A gamma variate function was then fit to the time-enhancement-curve and thereafter both the 'slope' of enhancement for each patient and the region of interest [ROI] were calculated. According to a univariate analysis, the slope of the time-enhancement-curve was found to correlate with the e' (r = 0.686, P = 0.000) and E/e' (r = -0.482, P = 0.007), however, no significant correlation was observed with the systolic parameters of the left ventricle. These results indicate that the slope of the time-enhancement-curve in the aorta significantly correlates with e', i.e. the diastolic parameters, which are independent of the systolic parameters. Based on these findings, we propose that the slope of the time-enhancement-curve may serve as a parameter for the left ventricular diastolic function on MDCT.     

Dynamic real-time 4D cardiac MDCT image display using GPU-accelerated volume rendering

Intraoperative cardiac monitoring, accurate preoperative diagnosis, and surgical planning are important components of minimally-invasive cardiac therapy. Retrospective, electrocardiographically (ECG) gated, multidetector computed tomographical (MDCT), four-dimensional (3D + time), real-time, cardiac image visualization is an important tool for the surgeon in such procedure, particularly if the dynamic volumetric image can be registered to, and fused with the actual patient anatomy. The addition of stereoscopic imaging provides a more intuitive environment by adding binocular vision and depth cues to structures within the beating heart. In this paper, we describe the design and implementation of a comprehensive stereoscopic 4D cardiac image visualization and manipulation platform, based on the opacity density radiation model, which exploits the power of modern graphics processing units (GPUs) in the rendering pipeline. In addition, we present a new algorithm to synchronize the phases of the dynamic heart to clinical ECG signals, and to calculate and compensate for latencies in the visualization pipeline. A dynamic multiresolution display is implemented to enable the interactive selection and emphasis of volume of interest (VOI) within the entire contextual cardiac volume and to enhance performance, and a novel color and opacity adjustment algorithm is designed to increase the uniformity of the rendered multiresolution image of heart. Our system provides a visualization environment superior to noninteractive software-based implementations, but with a rendering speed that is comparable to traditional, but inferior quality, volume rendering approaches based on texture mapping. This retrospective ECG-gated dynamic cardiac display system can provide real-time feedback regarding the suspected pathology, function, and structural defects, as well as anatomical information such as chamber volume and morphology.     

Imaging of the cardiac venous system: comparison of MDCT and conventional angiography

OBJECTIVE: Diagnostic and therapeutic strategies in electrophysiology and interventional cardiology include the coronary venous system. The purpose of this study was to compare MDCT angiography with conventional coronary sinus angiography in terms of detailed anatomic display of the coronary veins. CONCLUSION: MDCT angiography is a reliable alternative to conventional coronary sinus angiography for detailed anatomic display of the coronary veins.     

Right ventricle function assessment by MDCT

OBJECTIVE: The right ventricle is often overlooked on chest and even cardiac MDCT studies. This article will review the normal anatomy of the right ventricle on MDCT and the signs of its functional alterations. CONCLUSION: MDCT signs of right ventricular dysfunction should be known and checked in relevant cases, such as pulmonary embolism in particular, and in any disease that affects both the structure and function of the lungs in general.     

Considerations when introducing a new cardiac MDCT service. Avoiding the pitfalls

The widespread introduction of multidetector computed tomography (MDCT) into mainstream imaging departments has enabled many centres to undertake cardiac MDCT and, in particular, MDCT coronary angiography. This review highlights the areas that need consideration when introducing a new cardiac MDCT service and covers both technical and non-technical aspects. This includes equipment requirements, personnel, training, patient selection and preparation, cardiac CT protocols and post-processing techniques, and potential pitfalls.     

Normal anatomy and variants of the venous cardiac system in MDCT coronary angiography

Three separate venous systems drain the blood returning from the heart walls. These veins are characterised by remarkable variability in terms of frequency, size and course. The knowledge of cardiac venous anatomy is of primary importance during interventional cardiac procedures that require catheterisation of cardiac veins. Some anatomical variants may hinder or contraindicate access to target veins. Coronary angiography (CA) with multidetector computed tomography (MDCT-CA) and multiplanar reformations (MPR), maximum intensity projection (MIP) and 3D reconstructions provides noninvasive visualisation of normal cardiac veins and anatomical variants. The purpose of this pictorial review is to describe by MDCT-CA the anatomy and main variants of the cardiac venous system.