cardiac CT Flashcards
(45 cards)
why might cardiac ct be better than cathlab (theatre+xray)
- minimal invasive
- quick
- cheap
- visualise other tissue
- low d0se
see non flow limiting plaque
what is calcium scoring
uses special x-ray equipment to produce pictures of the coronary arteries to determine if they are blocked or narrowed by the buildup of plaque
- low dose
whats the levels of calcium score
0
5-7.5 = boaderline
7.5-20 = intermediate
20+ = high
why types of plaque have increase risk of rupturing in the heart and what does it look like on ct
- non calcified plaque (esp if it is flow limiting)
- dark region in artery (not bright as it isnt calcified)
main consideration for cardiac CT= flow rate, IV technique
why might you be referred for cardiac CT
- family history heart disease
- atypical chest pain
- previous stents/grafts
what contraindications are there for cardiac ct (why they would get one)
- arrhythmia
- cradycardia
- contrast issues
- astham
why can patient with asthma not have betablockers in cardiac ct
- beta blockers are used and beta 2 affects respiratory system
how is the heart rate measured with an ECG according to QRST value
heart rate = time b/w each R peak
where is the idea area for cannula insertions, what size cannula and which are and why
- antecubital fossa ( triangular dip on inner elbow)
- green cannula or bigger (18G)
- right arm, as theres larger vessels with decrease impact of pressure in flow
what flow rate for cardiac ct
7-8ml/sec
note: placement of contrast line is important as it can cause ECG artefact
how does rotational speed/shutter speed of the CT affect signal/image quality and dose
- increase speed (rotation time)/ decrease time taken for rotation = noisier images as less protons recieved by detector
- ’s’ in mAs is less so less dose
how do you decrease noise due to increase rotational speed (for fast imaging)
by increasing mA
- because increasing rotational speed decreases the ‘s’ in mAs, you have to increase mA to make up for the dosage.
therefore by making up the dose, noise gets reduced ( increase dose = decrease noise)
if 2 tubes and detectors are used, it will only need to do 1/4 rotation for whole slice to be scanned, thus time is greatly reduced. How does this affect temporal resolution
temporal resolution is resolution according to time, if time is greatly reduced, temporal resolution will increase
why would the cardiac ct be scanned at end diastole (region before R in QRST) (at 75% of cardiac cycle)
as the heart is filling (in diastole) its the slowest part of the cycle
what is a step artefact and why might this be seen in cardiac CT
reconstructions are from different cardiac phases. This is associated with heart rate variability and irregular heart rates.
- as multiple bits of data taken across heartbeat to form image, it can overlap/recontruct wrong
- looks like staggered/jaggered anatomy
- found with helical CT
how can you prevent the step artefact, what con is with this
- use axial protective gating
- image whole heart with wider detector
- cannot predict heart rate (as it isnt continuous) so may take image at wrong part of cycle
because not all people have 60bpm heart rate, what can you do for patients with faster heart rate
give betablocker (slow heart rate)
to scan faster what 3 things can you do
- faster rotation time
- 2 tubes
- faster table movement in helical acquisition
what can help cardiac imaging for patients with atrial fibrillation
scanner predicts next beat from last
(SAM) smart arrhythmia management (to record their heart rhythm themselves, portable ECG device)
xwhat can help cardiac imaging for patients with ectopic heart beat
ectopic rejection software
what iodine contrast is used in cardiac CT, what cannula
omnipaque 350 60ml/s
- green cannula
- 50mls NaCl
where is smart prep/ bolus timing starting from
ascending aorta
