ECG guidance is used to gate image acquisition over multiple cardiac cycles. Analyzing radioactivity counts within that identified region is important as this technique studies the changes in radioactivity in the left ventricle between the end-systolic phase and end-diastolic phase instead of truly measuring volumes of the left ventricle. LV region of interest is determined, following which the radioactivity counts within that region are analyzed. Planar imaging to calculate LVEF calculation requires differentiation of left and right ventricle with left anterior oblique projection. However, SPECT images can also be obtained. Planar images of the left ventricle are obtained. This is a technique in which a patient's red blood cells are labeled with technetium 99m pertechnetate. The two most commonly employed nuclear cardiac imaging modalities to calculate LVEF are gated equilibrium radionuclide angiography (multiple-gated acquisition scan) and gated myocardial perfusion imaging with either single-photon emission computed tomography (SPECT) or positron emission tomography (PET) radionuclide angiography. There are different techniques available to calculate LVEF. However, one has to take into consideration the patient's poor renal function and contrast allergies while using the contrast material, which can limit the use of this modality. Unlike the MRI, CT images are obtained with single breath hold. The definition of the endocardial border is directly related to the timing of the contrast bolus. Determining the LV shape is essential as this technique involves the tracing of the entire LV cavity using the Simpson method. This involves generating and tracing reconstructed short-axis cine images of the heart. LVEF can be calculated using the Simpson method. These measurements and contrast play an important role in differentiating the LV cavity from the endocardium. The automated methods are used, which depend on Hounsfield unit measurements. As a result, iodinated contrast is used, which helps in differentiating blood and endocardial borders. Lack of contrast results in poor differentiation on non-contrast CT images. Calculation of LVEF with MRI does not necessarily require the use of ionizing radiation or contrast material. A well-defined endocardial border can be obtained with the use of high contrast. LV shape needs to be determined in this technique as the entire LV cavity is traced. LV volume is then derived by the addition of the volumes of the slices. Multiplying the area of the tracing for each image slice by the slice interval (image gap + slice thickness) gives the volume of the slice. LV endocardial borders are manually traced on each short-axis image to obtain the ventricular cavity area for each slice. During the end-systole and end-diastole phase, short-axis images are obtained. Simpson disk summation method uses the short-axis cine steady-state free precession images of the LV to obtain LVEF. LVEF can be obtained with MRI using manual, semi-automated or automated methods. Compared to other echocardiographic methods, three-dimensional modality is known to be more accurate and far less variable because the entire LV cavity is detected. Unlike other M-mode and two-dimensional echocardiographic techniques, three-dimensional methods give a minimal explanation about the shape of the LV cavity. LVEF derived from this modality would mostly require the data to be obtained over several heartbeats using special three-dimensional imaging probes. The Teichholz method for calculating LV volumes from LV linear dimensions is no longer recommended for clinical use.īecause three-dimensional echo does not require geometric assumptions, it is felt to be the optimal way of measuring LVEF using echocardiography. This formula is meant to compensate for the deviation from the ellipsoid model seen in both unusually large and small ventricles. A modified ellipsoid model using unidimensional data: The septal-posterior wall dimension was substituted into a formula described by Teichholz based upon an ellipsoid model where the major axis is a variable function derived from the measured minor axis, D.
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