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Overview of the Process, Exclusions and Risks, and Preparation


Overview of the Process

Pre-Scanning Issues

Study Issues

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    Review the case history.

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    Establish:

    • The primary indication for the study

      • Other indications for the study

    • Contraindications to the study

    • The appropriateness of CT versus other alternative modalities for the indication and for the patient

  • □

    Select:

    • The optimal scanning protocol

    • The optimal radiation-lowering features

    • The optimal contrast injection technique

Patient Issues

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    Appropriate patient exclusion and selection

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    Appropriate preparation:

    • To ensure predictable contrast delivery, via the right side:

      • IV location: right antecubital vein

      • IV size: sufficient size (≥18G) to allow for the needed high flow rate (4–5 mL/sec)

    • To avoid problematic increase in heart rate during the study:

      • Ensure that the patient understands that there will be noise during the scanning.

      • Confirm that the patient understands that there will be a warm sensation during the study.

      • Consider β-blocker use; evaluate for risk-benefit ratio.

        • Short-term oral use

        • Use with or without IV supplementation

    • Administer sublingual nitroglycerin for coronary studies.

    • To achieve predictable position of the heart during the scan:

      • The patient must understand and practice consistent breath-holding for the study.

    • To avoid motion artifacts, the patient must understand that he or she must not:

      • Move during the scan

      • Take a second breath during the scan

      • Release the breath during the scan

      • Swallow during the scan

Scanning Issues to Resolve

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    Verification of protocol selection:

    • Decide whether or not to perform:

      • A noncontrast scan first

      • Calcium scoring

      • A delayed scan

    • Select gating mode:

      • Prospective gating

      • Retrospective gating

  • □

    Verify contrast injection:

    • Technique

      • Injection technique:

        • Single injection

        • Dual injection

        • Triple injection

      • Bolus technique

        • “Test bolus” method

        • “Bolus tracking” method

    • Rate, duration, and amount of injection

    • Site of injection

  • □

    Selection of an FOV that is suitable to capture both the superior and inferior extent of the region of interest (e.g., coronary tree). Recall that the breath taken during the study may not be of the same depth as the one taken for the topographic view that the FOV was selected on.

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    The greater the needed anatomic coverage, the greater the FOV, but the greater the FOV:

    • The greater the radiation dosage

    • The larger the voxel size

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    In order of increasing FOV size ( Fig. 2-1 ):

    • CTA of the coronary tree only

    • CTA with saphenous vein graft coverage

    • CTA with internal mammary arterial graft imaging

    • Pulmonary embolism (PE) protocol

    • Aorta protocol

    • Lower extremity vasculature

    Figure 2-1, Scout images obtained before a CT angiogram. The scout makes it possible to determine the appropriate field of view for the cardiac CT study.

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    Selection of technical factors appropriate for the patient’s body habitus (e.g., milliamps)

Post-Scanning

Quality Assurance Analysis

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    Verification that the achieved anatomic coverage is complete:

    • Did the upper limit of the scan capture the upper extent of anatomic interest?

    • Did the lower limit of the scan capture the lower extent of anatomic interest?

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    Verification of quality of the scan

    • Quality check:

      • Artifacts

      • Signal-to-noise ratio (SNR)

    • Quality assurance (QA) of the ECG:

      • Minimal heart rate change during the study

      • No arrhythmias

    • QA of the contrast technique:

      • Contrast opacification quality

      • If coronary CTA:

        • Left heart chambers and aorta: excellent contrast effect

        • Right heart: mild residual contrast effect

Image Reconstruction

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    Reconstruction of images from the data set as needed to address the referring question ( Fig. 2-2 )

    • Standard: axial, sagittal, coronal

    • With or without the following views:

      • Cardiac-specific

      • 3D

      • Maximum intensity projection

      • Curved multiplanar reconstruction

      • Straightened

      • Cross-sectional perpendicular view to the centerline (intravascular ultrasound view)

      • Other

    Figure 2-2, Tissue Doppler recording at the mitral annulus level in four different patients, all with corresponding ECG tracings. In each case the motion-free interval, the ideal phase for CCT image acquisition, is indicated on the last cardiac cycle of the tracing by a vertical red line. It can be seen that the motion-free interval is generally very short. The tracings in panel B reveal that lower heart rate is associated with a longer “diastasis” motion-free phase between early and late diastolic filling/motion, which allows for better quality CCT image acquisition.

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    If there is reason to be concerned that:

    • Image reconstruction did not depict the heart without motion in diastole:

      • Reconstruct the images at another phase of the cardiac cycle (e.g., 70%, 75%, 80%)

    • Image reconstruction did not depict the heart at end-systole:

      • Reconstruct the images at another phase of the cardiac cycle (e.g., 35%, 40%).

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