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Reformatted Four-Chamber and Short-Axis Views of the Heart Using Thin Section (≤2 mm) MDCT Images

Posted Aug 31, 2007 Updated Apr 7, 2023
By Michael T. Lu MD , Hale Ersoy MD , Ama G. Whitmore BA , Martin J. Lipton MD , Frank J. Rybicki MD PhD
6 min read

Rationale and Objectives

In cardiovascular computed tomography (CT), thin collimation results in a large number of images per examination. Moreover, interpretation relies on multiplanar reformatted images.

Materials and Methods

Although many strategies for approaching cardiac reformations have been described, as CT use increases, so does the importance of simple and reproducible postprocessing algorithms. The clinical importance of reformations has recently extended beyond the left ventricle to include the right ventricular in patients with pulmonary embolism.

Results

This work illustrates an algorithm to reformat two of the most important views in cardiovascular CT: the four-chamber and short axis views.

Conclusions

The illustration is performed in the context of two cardiovascular examinations: cardiac CT and CT pulmonary angiography.

Utilization of multidetector computed tomography (CT) for cardiovascular applications continues to increase. Robust electrocardiogram (ECG)-gated protocols are being used with increased frequency for assessment of coronary stenoses, so called “coronary CT angiography (CTA).” Because CT is acquired throughout the R-R interval, the size and function of the left ventricle can be evaluated with reformatted images viewed as a cine loop throughout the cardiac cycle ( ). The evaluation of pulmonary embolism (PE) represents another important use of CTA in CV imaging. In addition to the fact that CTA is a primary method to diagnose pulmonary embolism (PE), recent work suggests that prognostic information can be obtained by evaluating the size of the right ventricle ( ). Using multiplanar reformatted images to assess the size of the right ventricle has been proposed as a tool to help determine patient prognosis ( ).

With respect to image acquisition and reconstruction, thin collimation is a common theme for both coronary CTA and CT pulmonary angiography (CTPA). The resulting thin axial slices serve as the primary dataset from which reformatted views are obtained, despite the fact that the contrast-enhanced CT protocol for the detection of PE and the evaluation of coronary stenosis differ with regard to many factors including the contrast bolus timing, the use of ECG gating, the volume of contrast material, and the detector collimation. The details of the image acquisition for each specific vendor are beyond the scope of this work, but, as an example, at our institution ECG-gated coronary CTA is performed using a 64-slice system with 0.6-mm detector collimation. The axial slices for evaluation of the coronary arterial tree have a reconstruction interval of 0.4 mm. To assess the left ventricle, additional 2-mm thick images are reconstructed over 10 equally spaced phases (0%–90%) in the cardiac cycle. Additional phases (eg, 20 reconstructions at 5% intervals) could be performed and may be important in newer generation CT systems with temporal resolutions under 100 milliseconds. In our experience, the 2-mm thick images give good signal and do not overwhelm the three-dimensional image postprocessing hardware/software. For each patient, the four-chamber and short-axis views are reformatted. The short-axis view is used to compute left ventricular ejection fraction ( ), and a cine of the ten phases of the 4-chamber view is used as an overview (with short-axis views) for ventricular global and regional wall motion ( ). It is important to note that additional cardiac axes can be used to depict specific pathology (eg, the three-chamber view for evaluating mitral valve prolapse) ( ), but the present article is designed to give the radiologist who is just beginning the practice of cardiovascular CT a primer for those images that are required in a complete evaluation in every patient.

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Algorithm

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Figure 1, True axial, coronal, and sagittal views of the cardiac apex. The first step is identifying the cardiac apex on the standard axial (left), coronal (middle), and sagittal (right) views, and marking the apex with the cross-hair.

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Figure 2, Five consecutive 1.25-mm thick sagittal images though the mitral valve (white arrow). The valve plane is seen on several images.

Figure 3, The chosen sagittal image with one line (red) of the cross-hair positioned through the center of the mitral valve. Note that when the sagittal images are scrolled to visualize the mitral valve, the cross-hair remains in the same plane as the apex (as defined in step 1) and typically is seen within the right ventricular cavity.

Figure 4, Illustration of step 2. The long black line from the cardiac apex through the mitral valve defines the plane of a four-chamber view. The volume sketch in the upper left-hand corner shows the plane of the main illustration in relation to the surface of the heart.

Figure 5, Four-chamber view. This view is used to evaluate left ventricular wall motion abnormalities. The anatomic plane of the four-chamber view is shown in the top left hand corner. The larger illustration (middle) shows the orientation of the cardiac chambers. When computed tomography images are viewed in this plane as a cine loop, left ventricular wall motion can be assessed. The corresponding patient image (right) shows the cross hairs in the center of the mitral valve; this is the basis of step 3 in which the short axis views are created.

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Figure 6, Short-axis view at the base of the heart. Scrolling the images in this plane will give the short-axis stack to be used to calculate left ventricular volumes. The left hand image shows the orientation of the cross hairs at the end of step 3, namely after the creation of the short axis stack. As noted in the description of step 4, a four-chamber view aligned along the plane defined by the red line will not demonstrate the maximum diameter of the right ventricle. In the right hand image (step 4) the red line has been turned so that the four-chamber plane it defines includes the full extent of the right ventricle.

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Figure 7, Illustration of the “turn” used to optimally visualize the right ventricle. A dashed line was the result of step 3, the creation of the short-axis stack. The dashed line defined a plane through the right ventricle, but this plane does not fully represent the size of the right ventricle. This can cause an underestimation of the right ventricular diameter on four-chamber views. In step 4, the dashed line is “turned” to the solid line, with the centerpoint (cross-hairs) rotating through the center of the left ventricle. The plane defined by the solid line characterizes the full diameter of the right ventricle. The upper left-hand corner shows the plane illustrated with respect to the surface of the heart.

Figure 8, Four-chamber view after step 4 (see text) that demonstrates the full extent of the right ventricular chamber size.

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Discussion

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References

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Academic Radiology, Volume 14, Issue 9
Journals General Radiology
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