Coronary CT Angiography (CTA) Explained

• Coronary CTA (Computed Tomography Angiography) scanning is a cardiac imaging technique.

Cardiac CT Scans

• Several types of CT scans are used to diagnose heart disease.
• Calcium-score screening heart scan is one type of cardiac CT scan.
• Coronary CT angiography (CTA) is another type of cardiac CT scan used in heart disease diagnosis.

Cardiac CT for Calcium Scoring

• Cardiac CT for coronary calcium scoring is a non-invasive method.
• It provides information on the presence, location, and extent of calcified plaque in the coronary arteries.
• The coronary arteries supply oxygen-containing blood to the heart muscle.
• Calcified plaque results from the build-up of fat and other substances under the inner layer of the artery.
• Calcification signals the presence of atherosclerosis.
• Atherosclerosis is a disease of the vessel wall, also known as coronary artery disease (CAD).

Coronary CT Angiography (CTA) Uses

• Coronary CTA is useful for determining the cause of chest pain symptoms, especially in individuals at risk for coronary blockage.
• Risk factors include family history of cardiac events, diabetes, high blood pressure, smoking, and/or elevated cholesterol.

Risk Factors for CAD

• High blood cholesterol levels are a major risk factor.
• A family history of heart attacks is a major risk factor.
• Diabetes is a major risk factor.
• High blood pressure is a major risk factor.
• Cigarette smoking is a major risk factor.
• Being overweight or obese are major risk factors.
• Physical inactivity is a major risk factor.

Patient Preparation Prior to CT Scan

• Patients should wear comfortable, loose-fitting clothing during the exam.
• Patients may need to change into a gown for the procedure.
• Metal objects, including jewelry, eyeglasses, dentures, and hairpins, can affect CT images.
• Checking for contraindications should be done before CTA.
• No food should be consumed 3-4 hours before the scan.
• No caffeine should be consumed for 12 hours before the scan.
• Patients should receive instructions on how to breathe during the scan.
• An electrocardiogram (ECG) signal needs to be acquired.
• Heart rate control is necessary.
• Breastfeeding should be stopped until all contrast material has cleared from the body (about 24 hours after the test).
• Patients taking metformin should stop the medication before and after the procedure for 48 hours.

Patient Preparation - Heart Rate Control

• IV Beta Blockade is preferred for heart rate control.
• Administer 2.5 – 30 mg of Metoprolol to titrate the heart rate to 55-60 bpm.
• Monitor blood pressure while giving metoprolol.
• If the patient is asthmatic, consult a physician before administering beta blockers.
• The maximum dose of metoprolol should be 10mg for asthmatic patients.
• Consider calcium channel blockers like Diltiazem (bolus 0.25mg/kg) for asthmatic patients.
• Oral Beta Blockers can be used, administering 50 – 100 mg of Metoprolol 1 hour before the examination.

Breath Holding During CT Scan

• During the CT scan, a breath hold of 15–20 seconds will need to be performed.
• Practicing breath holding before the scan can help.

ECG Gating

• ECG gating is performed during the scan.
• First, clean the skin.
• Up to 12 self-adhesive electrodes will be attached to select locations on the arms, legs, and chest.
• Three ECG leads are attached to obtain an adequate ECG tracing.
• A noise-free ECG signal is important for synchronizing the ECG signal to the raw image data.

Cardiac Indications for CT Scan

• Emergency evaluation of acute chest pain.
• Cardiac evaluation of a patient with chest pain syndrome (e.g., anginal equivalent, angina) who is not a candidate for cardiac catheterization.
• For management of a symptomatic patient with known coronary artery disease (e.g., post-stent) when the results of the MDCT (Multidetector computed tomography) may guide the decision for repeat invasive intervention.
• For assessment of suspected congenital anomalies of coronary circulation
• Congenital coronary artery anomalies
• Coronary artery disease includes the evaluation of coronary atherosclerosis plaque
• Visualization of cardiac veins.
• Unclear findings after invasive coronary angiography (ICA).

Contraindications for CT Scan:

• Factors leading to potentially non-diagnostic scans, such as the inability of a patient to cooperate (e.g., breath-hold instructions and arm elevation).
• Contraindications against iodinated contrast media, nitrates, and β-blockers.
• Pregnancy or uncertain pregnancy status in premenopausal women.

Limitations of Coronary CTA:

• Any motion, including breathing and body movements, can lead to artifacts on the images.
• Coronary motion
• Slab artifacts, including ventricular ectopy and ventilatory motion.
• Calcium
• Stents

Coronary CTA Technique

• The patient should be in a supine position with both arms above their heads.
• ECG placement to monitor heart activity.
• Acquisition can be prospective ECG-gated or retrospective ECG-gated.
• Tube potential should be at 120kVp.
• The tube current should use automated current adjustment mode.
• Scout scan from pulmonary apices to below the heart.
• Scan direction should be craniocaudal.
• Contrast injection considerations.
• A contrast agent with high iodine concentration (350mg iodine/mL) is recommended.
• Contrast timing with a test bolus.
• The flow rate should be 5-6ml/s.

Scan Start and End Position

• Scan extent should be from the carina to below the heart.
• Note the overlap of the heart and diaphragm in the ending position of the scan.
• Observe the contour of the heart.
• Extend the scan approximately 2cm below the caudal extent of the heart.
• The position of the heart may change with inspiratory effort.

Scan Centering and Image Reconstruction

• Maximize spatial resolution for coronaries by centering the scan on the heart.
• CT resolution is greatest in the center of the scan field.
• Set the left-right position on the AP scout view.
• Move the table up-down to center on the aortic root and left ventricle.
• Reconstruction slice thickness should be 3mm for function and 0.5-0.8mm for coronary arteries.
• Use a sharper kernel for reconstruction if needed to visualize the coronary lumen with stents and calcified vessels.

Benefits and Risks of CT Scan

• CT examinations are fast and simple.
• CCTA is non-invasive, unlike cardiac catheterization with a coronary angiogram.
• CT is able to view bone, soft tissue, and blood vessels simultaneously.
• There are a few risks associated with CT scans.
• Skin damage or damage to blood vessels and nerves if contrast material leaks out from the vessel being injected.
• Renal failure is a risk factor.
• The radiation dose for this procedure varies.