Scans whole heart in one flash helical scan (red box in trace above)
Advantages
Doses are lowest
Mimimal movement artefact due to quick scan time
Disadvantages
Only works on consistent and low HR
One shot wonder. You only have what is captured in the one helical scan. No data manipulation afterwards
More prone to beam hardening and metallic artefacts
Scans blocks of the heart across multiple axial scans (red boxes in trace above). Not constantly scanning (on/off/on/off)
Will then stitch blocks together to create one image
The X-ray can be turned on for longer periods of the heart rate (increase size of red box) to increase amount of data obtained.
Advantages
Less prone to beam hardening under sampling and gives better dose modulation
Better for faster and irregular heart rates
Better for obese patients
Provides data from multiple different points in the cardiac cycle. Most of our scans will capture at least 5 different % time points available for reconstruction (eg 45%-70%)
Disadvantages
Higher dose than Flash
Susceptible to movement artefact between blocks
Mostly depends on the patient's heart rate. However other important factors can determine the protocol chosen:
Patient movement (better with Flash to minimize artefact)
Beam hardening artefacts: High patient BMI, metal implants, arms down (sometimes not enough dose produced on flash scans so step and shoot scan be better for this artefact reduction)
Anatomy: If a whole chest scan is needed as well then the gated CTA protocols may be better
Will trigger off end diastole when the heart is most still
Will trigger off end systole when the heart is the most still
Always sequential scan
Has longer periods of X-rays on (wider pink boxes on trace above) to allow for potential difference in beats
Link to RCH Coronary Protocol on Teams: Force CT-CP-714 CTA Coronary Gated FD Draft.docx