# Feasibility of ultra-low flow rate coronary CT angiography using photon-counting detector CT: a prospective randomized trial

## TL;DR

This study shows that using ultra-low contrast flow rates in photon-counting CT for coronary imaging can maintain image quality, making it a safer option for patients with difficult venous access.

## Contribution

First validation of ultra-low flow contrast rate coronary CT angiography using photon-counting detector CT.

## Key findings

- Ultra-low flow PCD-CT maintains objective image quality comparable to routine protocols.
- PCD-CT enables 50% contrast reduction without diagnostic compromise.
- Distal vessel clarity scores were modestly reduced in ultra-low PCD-CT compared to routine protocols.

## Abstract

This study evaluates the feasibility of photon-counting detector CT (PCD-CT)-based coronary CT angiography (CCTA) using ultra-low flow contrast rate while maintaining diagnostic image quality.

In this prospective trial, 292 patients underwent CCTA assigned to one of three protocols: ultra-low (1.5–1.8 mL/s) or routine (4.0–5.0 mL/s) contrast injection with PCD-CT, or routine injection with EID-CT. All scans utilized a high-pitch prospective electrocardiogram-triggering acquisition. PCD-CT images were reconstructed at 45 keV (ultra-low) or 60 keV (routine). Objective image quality was quantitatively assessed by measuring vessel attenuation, signal-to-noise ratio (SNR), and contrast-to-noise ratio (CNR). Subjective image quality parameters (vascular contrast, image noise, artifacts, and vessel clarity) were independently evaluated by two blinded readers using a 4-point Likert scale (1: non-diagnostic; 2: adequate; 3: good; 4: excellent).

Objective image quality demonstrated comparable attenuation, CNR, and SNR in proximal coronary segments across all groups (all p > 0.05). The ultra-low PCD-CT protocol significantly lowers attenuation in the distal LAD (373.20 ± 49.58 HU) compared to routine protocols (PCD-CT: 393.52 ± 49.38 HU; EID-CT: 396.72 ± 47.55 HU; p = 0.01). While distal vessel clarity scores were modestly reduced in distal vessel clarity (ultra-low PCD-CT: 2.91 ± 0.81 versus routine PCD-CT: 3.58 ± 0.50 versus routine EID-CT: 3.54 ± 0.50; p < 0.01).

For patients with difficulty establishing venous access routes, ultra-low contrast agent flow rates in PCD-CT maintain objective image quality comparable to that of standard protocols, with acceptable diagnostic performance despite slight reductions.

Photon-counting detector CT (PCD-CT) maintains objective coronary CT angiography image quality comparable to standard protocols even at ultra-low contrast flow rates (1.5–1.8 mL/s), offering a clinically acceptable and safer alternative for patients with challenging venous access.

First validation of ultra-low flow contrast rate CCTA using photon-counting CT (PCD-CT).Ultra-low flow rates maintain objective image quality (CNR/SNR) versus routine protocols.PCD-CT enables 50% contrast reduction without diagnostic compromise.

First validation of ultra-low flow contrast rate CCTA using photon-counting CT (PCD-CT).

Ultra-low flow rates maintain objective image quality (CNR/SNR) versus routine protocols.

PCD-CT enables 50% contrast reduction without diagnostic compromise.