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
11
Q
Scanning
A
- dual power pump with contrast and saline
- determine delay time (either timed bolus or bolus tracking method)
- inject 70-150 mL at 4-6mL/sec, 50mL saline
- MDCT thin slices, fast rotation, sync images to heart beat
- protocol depends of heart rate and site
11
Q
Post Scan
A
- no beta blocker = may leave right away
- beta blocker given = observe for 30 minutes
- reconstruct images as per site protocol
12
Q
Advantages of CT Guided Percutaneous Procedures
A
- precise, 3D localization of lesions
- permit planning of the access route (shows lesions and surrounding tissues)
- tip of needle can be visualize, small slices, can perform on small structures
- ability to accurately image high and low density material
- contrast may or may not be used (flexibility)
- easy access (can lower risk) to lesion as you change pt positions
13
Q
Sequential CT
A
- standard on CT scanners
- drawbacks are that it can make a case more lengthy as numerous single or helical images are obtained
- process: scan acquisition, place needle, scan, adjust, scan until correct location
- choppy intermittent visualization prohibits rapid adjustments
- dose reduction techniques: mAs should be set as low as possible (standard 250-175, down to as low as 30)
14
Q
CTF
A
- not standard on CT scanners and must be purchased separately (expensive)
- near real time visualizations, superior contrast resolution, 3D display
- dose reduction techniques: time and current as low as reasonably possible, use intermittent fluoroscopy
15
Q
Both Sequential and CTF
A
- can be done together depending on protocol
- personnel must use due diligence
- unacceptable to put hands in the CT beam
- use a lead drape to cover non-biopsy region can reduce scatter to pt and staff
16
Q
Indications for CT Guided Percutaneous Procedures
A
- variable; depends on site, rad, equipment
- abscesses
- pneumothoraxes
- biopsy of mass or lesion (abdominal or thoracic)
- percutaneous diseconomy of herniated disc, lumbar and pelvic interventions
- administration of chemo agents
- thermoablative treatments
- percutaneous vertebroplasty
17
Q
CT Guided Biopsies
A
- risk increases with the needle diameter
- risk increases with cutting needle
- overall complications are around 2%
- primary complication is bleeding (clotting is a factor). highly vascular lesions
- primary complication of lung biopsy is a pneumothorax during or after
18
Q
Biopsy Steps
A
- Explain procedure and obtain consent
- Examine lab values
- Plot scan
- Select area to preform biopsy, consider breathing
- Select best needle entry point, use metallic marker
- Prep skin, freeze
- Repeat scan to visualize the needle tip
- Confirm correct location and take tissue sample
- Post scan to confirm no complications
19
Q
CT Fluid Aspiration and Abscess Drainage
A
- similar to biopsy, same advantages
- shortest, straightest route is favoured along with unilocular, well defined, free flowing accessible site
- avoid major vessels, bowel loops and pleural space
- fluid collection can be done in one step or a catheter is left in place
- aspiration done to drain as completely as possible
- catheters are left to let gravity drain and are removed gradually once complete
