Customizing Contrast Medium Injection in Abdominal CT Saves Dose and Radiation

Background

Fixed contrast dosing is often used in abdominal CT, because it simplifies workflow. However, fixed dosing can lead to under- or overdosage of contrast media (CM) and variable enhancement in patients of different weights.

Total body weight has already been identified as the most effective factor for contrast customization (Bae 2008, Bae 2010, Heiken 1995).
To evaluate image qualities of customized versus standard abdominal CT injection protocols, Francesco Marci, University of Geneva, Switzerland, and US-American colleagues have used a weight-based, automatically customized injection protocol at low tube voltage (100kVp) and compared it to a standard CT at 120kVp with fixed contrast media volumes.

The injector software program used was personalized-patient-protocol technology (P3Tᵀᴹ) Certegra®, Bayer, Germany.

Conclusion

The automated customization of injection protocols with injector software programs decreases the total iodine load, while retaining good image quality at low kVp/KeV. The power injection software could also simplify and optimize workflow for busy CT practices.

Value Proposition

• Using P3Tᵀᴹ Certegra® for weight-based contrast customization in abdominal CT reduces injection rate and iodine dose: CM reduction was 10% on average compared to the standard dosing method.
• The customized protocol also led to lower flow rates, which is particularly interesting for oncology patients with poor vein integrity, note the authors.
• An optimized power injection software could also be an adjunct to technologists for easier customization thus reducing the risk of technologist-related errors and CM waste.
• If the software is adapted for low energy CT, CM volume could be reduced, which might decrease cost even further. Enabling low-energy protocols optimizes not only the total iodine dose, but also significantly lowers the radiation dose.

Methods

Retrospective Study

Patient Characteristics

• 174 patients in oncological follow-up with prior standard of care CT scan at 120 kVp within 15 months
• All patients later underwent low-energy abdomino-pelvic CT exams with customized injection protocols in the portal venous phase (PVP). Tube voltage was either 65keV or 100kVp.
• Patients were divided into three weight categories: ≤59.9kg; 60-89.9kg; ≥90kg

Contrast Media, Injector, Scanner

• Contrast medium: prewarmed (37°C) iopamidol 370 mg I/mL administered with 20-22 gauge cannula, followed by a 40mL saline chaser.
• Injector: MEDRAD® Stellant with P3Tᵀᴹ software
• Standard CM Dosing was: 
  ≤59.9kg: 80mL; 60-89.9kg: 90mL; ≥90kg: 120mL with an injection rate of 2-3mL/s for monophasic CT scans.
• P3Tᵀᴹ Certegra® customized injection (Fig 1)
• Fixed injection duration of 40s for monophasic scans in PVP; the software adapted the injection rate accordingly.

Scan technique

• Fixed injections with single energy CT (SECT) at 120kVp tube voltage for all prior exams
• Low-energy CT with either SECT with 100kVp or dual energy CT (DECT) reconstructed at a 65keV monochromatic level for follow-up exams.

Image Analysis

• Quantitative image analysis by one reader with 10 years experience and blinded for review. Attenuation (HU) and its standard deviation (SD) were recorded as the average of multiple regions of interest (ROI) within the liver and the pancreas.
• To assess image quality, signal-to-noise-ratio was calculated for various ROIs. They were compared between the low-dose and the standard-dose protocol, as well as between the weight categories between each type of protocol.
• Qualitative image analysis was independently performed by two experienced abdominal radiologists: They assessed organ contrast enhancement and overall image quality on a 5-point Likert scale.

Radiation 

• Radiation dose information was obtained from PACS.
• The volumetric CT does index and the dose length product for the PVP were recorded.

Results in Detail

Patient Characteristics

• 91/174 patients received customized injection with SECT at 100 kVp
• 83/174 patients received customized injection with DECT at 65 keV

Injection Parameters

• CM volume reduction with individualized injection varied by weight groups.
• With customized injection, CM volumes were markedly reduced (15–23%) for individuals
  • between 60 and 70 kg (70–75 mL vs. 90 mL) and
  • between 90 and 95 kg (93–100 mL vs. 120 mL).
• Customized injection resulted in a CM volume increase for individuals weighing between 83 and 89.9 kg: They received between 91–97 mL compared to the 90mL fixed injection.

Image Quality

• All CT scans were considered diagnostic.
• Attenuation was significantly higher for both SECT-100kVp and DECT-65keV protocols with customized injection compared to the standard protocol.
• Image noise was significantly lower for both SECT-100kVp and DECT-65keV protocols with customized injection compared to the standard protocol.
• SNR and CNR for liver and pancreas were significantly greater in images with customized injections.
• Between weight categories, no significant attenuation differences were found between 60-89.9kg and 90kg patients for liver and pancreas in SECT-100kVp and DECT-65keV. 
  For patients 59.9kg body weight, attenuation was significantly greater for liver and pancreas compared to the heavier patients in SECT-100kVp and DECT-65keV.

Radiation Dose

• Radiation doses were significantly lower in patients with SECT 100kVp compared to SECT 120kVp.
• No significant radiation dose differences were found between DECT 65keV and SECT 120kVp