Cardiac CT (prospective high-pitch acquisition)

The prospective ECG-gated high-pitch dual-source CT cardiac angiogram is a high pitch helical acquisition of the heart that is able to capture a single phase of the cardiac cycle, a dual-source scanner is required to perform it. Although this is the CT cardiac angiogram with the lowest dose it also has strict patient requirements for a successful exam. 

Indications

Please refer to our coronary CT angiography article for general indications.

Purpose

The purpose of the prospective ECG-gated high-pitch dual-source is opacification of the coronary arteries without motion artefacts. This is achieved best by prospectively scanning at the mid to end-diastolic phase (around 70% of the R-R interval) ¹. 

The exam is fast (250-300 milliseconds) ^2-4 but requires cooperative patients, a stable sinus rhythm and a heart rate of fewer than 60 bpm (this might vary between institutions) and a maximum patient weight of 100kgs.

For patients that do not meet these criteria see:

• heart rate ≥60 bpm sinus rhythm
  • prospective ECG gated (step and shoot) protocol
• atrial fibrillation/arrhythmia
  • retrospective ECG gated helical protocol

Practical points

• this scan is only performed on dual-source scanners
• body habitus plays a big role in scan quality, often larger patients are not suitable candidates for this scan
• this exam is the fastest, lowest dose CT cardiac exam but it is susceptible to artefacts and given it is prospective acquired it is difficult to fix. Ensure to check reformats and ECG data to ensure the acquisition was performed correctly
• for higher heart rates (>80bpm) consider end-systole acquisition (30-35% of R-R interval ²
• each artery will suffer from motion artefact at different phases, the following intervals are the best ‘windows’ to prevent movement for different arteries ¹
  • right coronary artery 
    • 40% of R-R interval
  • left anterior descending
    • 60-70% of R-R interval
  • left circumflex artery
    • 50-60% of R-R interval
• ​​some institutions will use higher iodine concentrations to increase attenuation