Why CT Scan Power Index (CTSPI) Is Better Than Heat Capacity as an Indicator of CT Tube Performance

A relatively unknown CT scanner specification, the CT Scan Power Index (CTSPI), is a better alternative for characterizing modern CT scanners' x-ray tube performance compared to the widely used (though outdated) specification, tube anode heat capacity. CTSPI allows hospitals to make apples-to-apples comparisons of different systems' tube performance—something that is no longer possible by comparing anode heat capacity values due to changes in tube technology and materials.

The CTSPI specification is not new. It came into effect in 2010 in the International Electrotechnical Commission (IEC) standard 60613, Electrical and Loading Characteristics of X-ray Tube Assemblies for Medical Diagnosis, third edition (which remains the most current version). Although CTSPI has been available for more than a decade, it has not been adopted by many users or manufacturers. Nevertheless, it is a more clinically relevant measure than heat capacity, having been developed with more recent tube designs, scan types and durations, and throughput needs in mind, and ECRI encourages hospitals to start using this specification instead of tube anode heat capacity.

This article reviews how CTSPI is defined and why heat capacity is no longer an appropriate indication of CT scanner performance.