CCTA

• Cardiac CT


  Studies of the heart and coronary arteries require dedicated CT acquisition technique in order to produce images free of motion artifact
• Cardiac CT


  • CM administration must be carefully monitored to ensure optimal enhancement
  • Challenges: coronary arteries are of relatively small caliber, tortuous in shape and rapid motion
• MDCT technology


  1. Heart rate management by the administration of beta-blockers

  2. Cardiac gating
• Pharmacologic heart rate control

  • Many institutions use β-blockers as part of their protocols
  • β-blockers are used to lower the heart rate to less than 60-65 bpm and to make the rhythm more regular
  • The negative chronotropic and dromotropic effect of the β-blockers lengthen the diastolic phase in the cardiac cycle
• To avoid complications, guideline should be followed when β-blockers are considered
• Protocols for β-blockers


  • Oral
  • IV
  • Combination
• β-blockers


  • Metoprolol tartarate
  • acebutolol
  • atenolol
  • betaxolol
  • bisoprolol
  • esmolol
• Effects of oral dose

  Seen within 1 hour of administration
• Effects of IV dose

  1. 10 mins after administration
• Contraindications for β-blockers


  • Sinus bradycardia
  • Systolic blood pressure <100 mmHg
  • Allergy to the medications
  • Decompensated cardiac failure
  • Asthma treated with β-agonist inhaler
  • Active bronchospasm
  • 2nd or 3rd degree of AV block
• The decision to give β-blockers and the dosage to be given should be made by a physician and is beyond the scope of the CT technologist
• Some institutions also give GTN sublingually at 0.3-0.4 mg immediately prior to CCTA to dilate vessels to improve visualization
• GTN administration helps to prevent coronary spasm that can mimic stenosis on the CT image
• ECG-gating


  To minimize cardiac motion artifact
• Most CCTA protocols use images acquired during the point of cardiac cycle with the lowest cardiac motion
• Prospective ECG-gating


  Also known as step-and-shoot/sequential scanning. This method seeks to identify the area of lowest cardiac motion and acquire images only in those portions of the cardiac cycle
• Retrospective ECG-gating


  Acquires images throughout the cardiac cycle while the patient's ECG is recorded. Images are later reconstructed to create image sets at any desired phase of the cardiac cycle
• To understand the method of ECG gating, a basic understanding of the ECG tracing is necessary
• Prospective ECG-gating CCTA


  1. Use a signal, usually derived from the R-wave of the patient's ECG, to trigger image acquisition

  2. A delay between the R-wave and scan initiation can be selected by the technologist

  3. Using this trigger, and the preprogrammed delay, a scan is acquired during a finite portion of R-R interval

  4. The table is then move to the next position, and the procedure is repeated until the entire area of interest is covered
• Prospective ECG-gating CCTA


  • Dramatic reduction of radiation dose
  • Type of gating is very sensitive to cardiac motion artifacts and image misregistration especially in patient with irregular HR
• Retrospective ECG-gating CCTA


  1. Acquires helical mode data acquisition throughout the cardiac cycle

  2. Using the ECG-tracings that are required with the scan acquisition, images are reconstructed in specified portions of the cardiac cycle

  3. In general, the reconstruction phase is performed at 60% to 75% of the cardiac cycle
• Axial image reconstructions


  Often referred to as the 'source images' because these images are used to create 3D and other image model
• Retrospective ECG-gating CCTA


  • High radiation dose to patient
• Methods to reduce radiation dose in Retrospective ECG-gating CCTA


  1. Reduce kVp setting

  2. Tube current modulation (ECG)
• Contrast administration


  • Standard screening for CM contraindications
  • IV line is placed using a large-lumen (20 G or larger) flexible cannula in a vein of sufficient diameter to accommodate high injection rate
  • A LOCM or IOCM, non-ionic agent with [iodine] of 300-400 mg/ml with an injection rate of 3-6 ml/s
  • Volume 70-150 depending on the scan protocol, scanner type and the patient's weight
• Target enhancement


  Typically in the range of 200-300 HU depending on specific indications
• Accurate timing for CM administration

  Essential. Attempts to set at 20 s for all patients have been unsuccessful. The delay time use must be patient specific
• Optimal time for CM administration


  Can be calculated for each patient using either timing bolus or bolus tracking
• ROI monitoring


  • Ascending aorta for coronary arteries (120 HU)
  • Left atrium for pulmonary veins
• CM is immediately followed by a saline solution bolus


  • Make use of the wasted CM present in the IV tubing and arm vein
  • Allows more homogeneous opacification throughout the examination where more uniform HU from the top of the aorta to the base of the heart
  • Reduces streak artifact over the SVC
• Breath-hold


  • It is very important that the patient suspend respiration during scan acquisition
  • Breathing during the scan will result in motion artifacts
  • Careful breath-hold instruction should be given to the patient before the scan begins; moderate inspiration is most frequently used
• CT coronary calcium screening

  • Calcification is a marker of CAD
  • Patient with CAD may exhibit with no symptoms of the disease
  • In many patients, myocardial infarction is the first sign of CAD
  • The goal of calcium scoring is to determine the location and extent of calcified plaque in the coronary arteries
• CT can predict the likelihood of subsequent cardiovascular events in people with no symptoms
• CT coronary calcium screening is frequently performed as a screening study for patients with risk factor for CAD but no clinical symptoms
• Calcium score


  The amount of calcification on cardiac CT is expressed as a calcium score
• Negative examination


  Shows no calcification within the coronary arteries and suggests that atherosclerotic plaque is minimal and that the chance of CAD developing during the next 2-5 years is low
• Positive test


  Means that CAD is present, regardless of whether or not the patient is experiencing any symptoms
• Methods of scoring


  • Agatston Score
  • Calcium volume score
  • Absolute calcium mass measurement
• A 4-detector row CT with a 0.5-second GRT is the minimal equipment requirement for a coronary calcium score measurement
• Imaging of coronary calcifications


  1. Performed using a low-dose technique without contrast enhancement

  2. The scan time is short as possible to avoid artifacts from cardiac motion and breathing

  3. Either step-and-shoot or helical acquisition mode can be used

  4. The patient is supine and the scan extends from the mid-level of the left pulmonary artery down to the diaphragm