Establishing a quality assurance program for photon counting detector (PCD) CT: Tips and caveats

Area of Science:

• Medical Imaging Physics
• Radiological Sciences
• Diagnostic Imaging Technology

Background:

• Photon-counting-detector CT (PCD-CT) offers unique capabilities beyond conventional CT systems.
• Evaluating PCD-CT performance requires specialized quality assurance (QA) protocols.
• The American College of Radiology (ACR) CT quality control (QC) manual provides a framework for CT system evaluation.

Purpose of the Study:

• To assess the adequacy of an ACR CT QC manual-based QA program for evaluating a clinical PCD-CT system.
• To determine if the existing QA program can fully assess the advanced features of PCD-CT technology.

Main Methods:

• Implemented a daily QA program assessing CT number accuracy and artifacts in standard and ultra-high-resolution (UHR) modes.
• Conducted a full system evaluation using the ACR CT Accreditation Phantom and routine protocols.
• Reconstructed images at various keV levels and evaluated spatial resolution via modulation transfer function (MTF) and iodine insert accuracy.

Main Results:

• The QA program successfully identified detector issues requiring recalibration or replacement.
• CT number accuracy varied by image type; 70 keV virtual monoenergetic images (VMIs) met ACR criteria, while others did not.
• Spatial resolution exceeded ACR phantom limits (~40 lp/cm vs. 12 lp/cm), and iodine quantification was accurate across VMIs.

Conclusions:

• Careful selection of protocols and parameters on PCD-CT systems is essential for meeting ACR accreditation standards.
• Utilizing the 70 keV VMI enabled the system to pass all ACR CT manual tests.
• Comprehensive PCD-CT evaluation necessitates supplementary tests like MTF measurements and multi-energy phantom scans.