Which method tracks the patient's heartbeat to make reconstructions during the relaxed phase?

The method that tracks the patient's heartbeat to make reconstructions during the relaxed phase is known as retrospective ECG gating. This technique involves continuously monitoring the patient's electrocardiogram (ECG) signal throughout the CT scan. As the heart beats, the ECG gating allows for the acquisition of images at specific phases of the cardiac cycle, with a preference for the diastolic phase, which is when the heart is more relaxed.

By utilizing retrospective gating, the images can be reconstructed from data collected during various phases of the cardiac cycle. This enables the technologist to select the optimal images that correspond to a preferred cardiac phase, thereby improving image quality and reducing motion artifacts caused by the heartbeat.

In contrast, other methods such as prospective ECG gating involve collecting data at predetermined intervals that correspond to the heart's rhythm rather than continuously monitoring and utilizing all of the data for reconstruction. Cardiac synchronization and phase contrast imaging refer to different techniques that are not primarily used for reconstructing images in relation to the heart's relaxed phase.