Heart Flashcards
What are the ways bolus timing can be achieved in Contrast enhanced cardiac scan
- Empirical delay of contrast 25 s - poor quality
- Bolus tracking - selected ROI, usually ascending aorta scanned intermittently following contrast injection, the full scan is auto triggered after a short delay once ROI enhanced to preset value
- Test bolus - a small initial injection of contrast )eg. 20 to 30 ml with 40 ml saline chase bolus is given. The ROI is scanned and time to peak enhancement derived. Full scan then performed using this delay. Usually add 3 seconds for max coronary enhancement. most reliable and accurate method - confirms patent IV - prepares patient for final scan
What are the imaging views for coronary arteriography
What is the scanning protocol for CT coronary angiography ?
- Scans are ECG-gated to allow prospective ECG triggering of the scan whenever possible with exposure only during specific points of cardiac cycle (mid to late diastole - for coronary artery images). Prospective non contrast scan 65-80% of RR interval over 3-4 cardiac cycles.
-used to detect and quantify calc - Calcium score - age and sex matched - detect and quantify coronary artery calcification - screening tool for subliminal cardiac disease - associated with low risk of event even though doesn’t exclude atheroma absolutely
In non contrast prospective
- if triggering not possible - modulate tube current by decreasing exposure during parts of cycle where image quality is not crucial (systole and early diastole) to reduce dose or to allow retrospective reconstruction times to specific points of the cycle
Plain scan the used to plan range of subsequent contrast enhanced
- Cardiac/ECG gating - triggers scan during specific point of cardiac cycle. Obtains high quality scans void of pulsation artifact
Compare prospective, retrospective and single beat acquisition cardiac scans
Retrospective:
Helical acquisition through cardiac cycle.
Retrospective reconstruction from data acquired during diastole (75% of RR)
High dose - 13 mSv- higher heart rates and less stable rhythms for graft assessment and where date from entire cycle required (functional)
Modulation of tube current in systole and early diastole used to decrease radiation by up to 50%. Image quality decreased in those parts but functional data preserved
Single beat acquisition: acquires data from whole heart in one cycle using wide-area detector covering the whole volume of the heart or dual source high pitch helical acquisition. - requires cooperation, low heart rate, very stable rhythm and gives low dose around 1 mSv and reduced contrast media volume
Prospective - image
What dose of beta blocker if needed should you give before CT coronary angiogram
Metoprolol 5-30 mg IV in portions of 5 mg nitrates against the HR
Or 100 mg oral 1 hr prior scan
IV can be given to top up po
What should be given a few minutes before CT coronary angiogram to dilate coronary arteries
SL glyceryl trinitrate (GTN) - 400 to 800 micrograms (1-2 tablets) or 1-2 sprays
Give99-120 seconds prior to scan to combat transient physiological elevation of heart rate
C/I - hypotension, severe AV stenosis , HOCM, recent MI, severe anemia, recent Viagra type meds
What sequences are used for cardiac MRI ?
Localizer images - fGRE or SSFP (long axis and short axis steady state free precession)
Thoracic overview, cardiac morphology - HASTE black blood imaging
Myocardial perfusion - Dobutamine stress imaging, early vs late GAD enhancement
MRA - 3D T1SSFP - coronaries - navigator respiratory gating
Or 2D breath hold - SSFP
Contrast - volumetric 3DT1fGRE
Technique for radionuclide ventriculography
- Supine
- ECG trigger signal connected
- m 99 Tc pertechnetate
- 1 minute post injection scan started
What radiopharmaceutical and amount is used for radionuclide myocardial perfusion imaging?
m 99 Tc MIBI or sestamibi 800 MBq
