R Perez Franco*, M Hoerner, Yale New Haven Health System, Yale School of Medicine, New Haven, CT

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  R Perez Franco

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(Saturday, 3/26/2022)   [Central Time (GMT-5)]

Purpose: Evaluation of dose and image quality based on input heart rate (HR) in cardiac imaging utilizing adaptive tube-current modulation (aTCM).

Methods: An adult electron density phantom with iodine inserts was scanned using aTCM on dual-source CT scanner using single segment helical reconstruction techniques. A cardiac wave generator was used to set the HR. Scans were acquired as a function of HR. The data was reconstructed to optimize the image quality based on EKG waveform. All parameters were extracted from the image header and then evaluated to measure the contrast to noise ratio of each insert in the phantom. A 0.6cc thimble chamber was used to sample the pulse width for each acquisition. In addition, 19 consecutive patient scans were collected over a six-month time period.

Results: The measured pulse width was 150 ms regardless of HR which is a little more than half rotation time (0.25s). The relationship between HR and dose is described by the fraction of R-R interval that the beam is on, where dose is expressed as weighted CTDI, not the standard CTDIvol. This is because the table speed must be adjusted based on the HR to avoid any gaps in acquisition between scans. This relationship begins to breakdown with increasing variability of the HR. The protocol uses an algorithm to maintain CNR at various kVp stations. Therefore, dose is increased at higher kVp and for patients with larger diameter. To correct for this, the CTDIw was corrected using a kVp and mA correction factor (for only patient scans). The kVp tended to be higher for smaller HR’s (55-70 bpm).

Conclusion: Dose and image quality are a function of both heart rate and size which determine proper techniques. When evaluating Cardiac CT protocols for dose, one needs to consider the scan mode, HR, and patient size.

ePosters

• 174-60704-16021654-182529-546295063.pdf (R Perez Franco)

Keywords

Dose, Gating, CT

Taxonomy

IM- CT: Perfusion imaging, CTA, coronary artery calcium scoring

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