Automated Individualized Protocols Optimize Coronary CT Angiography

Background

Vascular attenuation of coronary arteries in coronary CT angiography (CCTA) mainly depends on contrast media (CM) injection parameters, CT scan technique, and patient-related factors. However, patient characteristics such as patient weight are not considered in fixed CT protocols. Patient weight has been suggested to correlate with vascular attenuation, and therefore with diagnostic image quality.

Casper Mihl et al., Maastricht University Medical Center, Netherlands, analyzed vascular attenuation, image quality, and injection parameters across different body sizes. In their comparative study, one group received an individualized protocol calculated with an automated contrast injection software (P3Tᵀᴹ Bayer), the other group received a fixed CCTA protocol.

Conclusion

Individualized CCTA protocols can reduce contrast media volume without compromising diagnostic attenuation. In this study, automated body weight-adapted contrast media injection in CCTA showed diagnostically sufficient vascular attenuation across all body sizes. Contrast volume, flow rates, and peak pressure were lower than in fixed protocols in the majority of patients.

Value Proposition

The Medrad® Centargo CT injection system with the P3Tᵀᴹ software solution and Ultravist® 300 mg I/mL showed a benefit for individually tailored contrast media injection: Optimal diagnostic attenuation of coronary segments was achieved while using less contrast media volume in the majority of patients (Fig. 1).

Methods

Patient Characteristics

• 265 patients with suspected coronary artery disease (CAD)
• Group 1 (141 patients): individually adapted injection protocol
• Group 2 (124 patients): fixed injection protocol

Injection Parameters

• Contrast medium: prewarmed (37°C) iopromide 300 mg I/mL (Ultravist®)
• Injector: MEDRAD® Centargo CT injection system with P3Tᵀᴹ software
• Individual protocols: Flow rate according to tube voltage and body-weight adapted iodine delivery rate (IDR) and total iodine load calculated with the P3Tᵀᴹ software
• Fixed protocols: Flow rate of 7.2 mL/s
• Scan technique: Dual Source CT

Attenuation and Image Quality Evaluation

• Attenuation measurements by two blinded readers in consensus
• Attenuation values 325 HU or greater were considered diagnostic
• Subjective image quality evaluation by one radiologist and one cardiologist in consensus on a 4-point scale (4 = excellent, 1 = non-diagnostic)

Data Monitoring

• Injection pressure, flow rate, and total amount of CM monitoring with Certegra P3Tᵀᴹ (Bayer)

Results

Attenuation and Image Quality Evaluation

• No significant differences in subjective scan quality between groups (p = 0.311).

Group 1 (Individualized Protocol)

• Sufficient overall enhancement levels (>325 HU) were achieved in all weight groups.
• No significant differences in mean attenuation values between different body sizes (p > 0.173).

Group 2 (Fixed Protocol)

• Significantly lower attenuation levels in higher weight groups
• Markedly increased enhancement levels in lower weight group
• Proximal vs. distal mean attenuation values decreased significantly within higher weight classes.
• Mean attenuation of the distal left anterior descending artery (LAD) for patients weighing 95–109 kg did not reach diagnostic values (305 ± 35 HU).

Injection Parameters

• Group 1 had less CM volume, lower peak flow rates, and decreased peak pressures in patients weighing <95 kg compared to Group 2.
• Mean CM volumes for Group 1:
  • 55 ± 6 mL (39–59 kg)
  • 61 ± 7 mL (60–74 kg)
  • 71 ± 8 mL (75–94 kg)
  • 84 ± 9 mL (94–109 kg)
• Mean CM volume for Group 2:
  • 75 ± 0.1 mL
• Mean peak flow rates varied between 5.4 ± 0.1 and 7.7 ± 0.4 mL/s in Group 1 (Group 2: 7.5 mL/s)
• Mean peak pressures varied between 89 ± 4 and 128 ± 12 psi for different weight groups in Group 1 (Group 2: 122 ± 9 psi)