Week 9: Cardiac Ct Angiography Flashcards
1
Q
Cardiac CTA Introduction
A
- latest non invasive technology for diagnosing CAD and cardiac function
- MDCT technology has evolved improving temporal and spacial resolution
- volume scanning with ECG gating mode
2
Q
Indications for CTA
A
- low/intermediate likelihood of CAD
- patients with high likelihood will more often get traditional angiography because intervention is often needed
3
Q
CTA Assesses What?
A
- coronary artery abnormalities
- left ventricular function
- congenital cardia morphology
- great vessel and pulmonary vasculature
- stent and post CABG
4
Q
Manageable Contraindications
A
- high HR of more than 80bpm with arrhythmia
- severe previous idiosyncratic allergy to CM
- claustrophobia
5
Q
Absolute Contraindication
A
renal impairment
6
Q
Coronary Arteries
A
- small diameter (1-4mm)
- complex anatomy
- rapid motion
6
Q
Heart Rate and Beta Blockers
A
- to reduce motion artifacts the patients HR is temporarily lowered by administering beta blockers
- used to lower HR to less than 65-70 bpm and to make rhythm more regular
- nitroglycerin given sublingually to dilate vessels, improve visualization and prevent coronary spasm from mimicic stenosis
6
Q
Retrospective ECG Gating
A
- helical data acquired throughout cardiac cycle and images are then reconstructed in specified portions of the cardiac cycle
- general rule is that image reconstruction os performed at 60-65% of the cardiac cycle
- high radiation dose, mA modulation decreases tube current during systolic phase
- preferred method for pts with arrhythmias
6
Q
Why is high speed/temporal resolution needed for CTA?
A
- heart and coronary arteries are in continuous motion
- reduce effects of patients movements on image quality
- short both hold makes for a more comfortable scan
- less amount of IV CM needed
6
Q
Arrhythmic Patients
A
- real time adaptive scanning avoids up to 50% of unanticipated premature beat arrhythmias
- system adaptively avoids scanning during heart cycle post irregular beat
7
Q
ECG
A
- provides a profile of the hearts electrical activity with time
- each normal heart beat exhibits similar characteristic pattern consisting of 5 waves
- distance between two R waves represents one cardia cycle referred to as R-R interval
7
Q
ECG Triggering/Gating
A
- a technique for cardia Ct to reconstruct images acquired during specific period of cardiac cycle
- protocols use images acquired during the point of the cardiac cycle with the lowest cardiac motion (T wave)
8
Q
Prospective ECG Triggering
A
- also called sequential; or cine-mode scanning
- acquires images only in the portions of the cardiac cycle expected to have the least cardiac motion (t wave)
- uses a signal, usually derived form the R wave to trigger axial mode image acquisition
- minimizes radiation dose
- very sensitive to cardiac motion artifacts and image misregistration
- particularly problematic with patients with arrhythmias
9
Q
Common Cardiac CTA Protocol
A
- scouts PA and Lat, one could be enough
- low dose prospective ca-score scan (pre CM scan)
contrast timing ether bolus tracking or test bolus - contrast injection using mixed mode
- slice thickened of 0.625 mm
- center R peak delay (acquiring in diastolic phase)
- start: 1cm below carina
- end: just below heart apex
10
Q
Patient Preparation
A
- arrives 1 hour early
- no caffeine 12 hours prior
- obtain history, explain procedure, Strat IV
- connect ECG leads
- position patient, asses HR
- consult rad if HR over 65 or arrhythmia
