cardiac imaging

Subdecks (10)

Cards (251)

  • Cardiac Angiogram
    Imaging technique to visualize the coronary arteries
  • Cardiac Intervention
    Procedure to treat blockages in the coronary arteries
  • Indications for Coronary Angiography

    • Coagulopathy
    • Decompensated congestive heart failure
    • Uncontrolled hypertension
    • CVA
    • Refractory arrhythmia
    • GI hemorrhage
    • Pregnancy
    • Active infection
    • Renal failure
    • Uncooperative patient
    • CM allergy
  • type of catheter in of Coronary Angiography

    • Catheter
    • Diagnostic catheter
    • Guiding catheter
  • Cardiac CT

    Studies of the heart and coronary arteries require dedicated CT acquisition technique in order to produce images free of motion artifact
  • Catheter size
    4F-14F for diagnostic, 6F-16F for interventional
  • 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
  • Catheter type

    Radial artery route: optitorque
    Femoral route: Judkins Lt/Rt, tiger
    Ventriculogram: pigtail
  • MDCT technology

    1. Heart rate management by the administration of beta-blockers
    2. Cardiac gating
  • Angiographic views of Left Coronary Artery

    • AP
    LAO cranial
    LAO caudal
    RAO caudal
    RAO cranial
    Lateral
  • 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
  • Angiographic views of Right Coronary Artery

    • LAO
    RAO
    RAO cranial
    LAO cranial
    Lateral
  • To avoid complications, guideline should be followed when β-blockers are considered
  • Grading stenosis
    Comparing the area of narrowing to an adjacent normal segment, and calculating the percentage reduction
  • Protocols for β-blockers

    • Oral
    • IV
    • Combination
  • Ejection Fraction

    Measure of how much blood the heart pumps out with each contraction
  • β-blockers
    • Metoprolol tartarate
    • acebutolol
    • atenolol
    • betaxolol
    • bisoprolol
    • esmolol
  • Causes of decreased Ejection Fraction
    • Weakness of heart muscle
    Heart attack damage
    Problems with heart valves
    Long-standing/uncontrolled high blood pressure
  • Effects of oral dose

    Seen within 1 hour of administration
  • Causes of poor angiograms

    • Patient factors: size, movement
    Hardware/devices: pacemaker, multiple surgery clips
  • 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