The 2017 CT QC Manual (Revised 9-24-2024)

Revision History

CT sites applying for accreditation for the first time or renewing will receive an electronic copy of the manual by email and can be located on the Medical Physics Resources webpage. 

The purpose of the ACR CT QC manual is to help guide facilities in establishing and maintaining an effective CT quality control program and to provide a reasonably uniform approach to testing. The manual provides a minimum set of tests required to ensure that a scanner performs in a consistent manner and yields acceptable images. There is a great diversity in scanner technology, phantoms, testing procedures and tolerances. The vendor’s specific quality control program should be followed and can be a substantial part of a QC program. When these tests and phantoms are available, they can be used to fulfill the ACR CT Accreditation Program QC requirements. In some cases, using the manufacturer’s recommended QC protocols, procedures, and frequencies may be a condition of maintaining warranties as well as purchase or service agreements. The ACR CT QC manual is certainly not intended to override or replace any such conditions. Indeed, there may be instances where the ACR CT QC manual’s described tests may not be appropriate for a specific test on a specific scanner. Use of the manufacturer’s phantom, testing procedure and specifications, especially in these situations, is appropriate and encouraged. Some known special cases are addressed in our article on special considerations in CT Accreditation Phantom Testing . 

While the required tests in the manual’s 2017 version are the same as the 2012 version, many of the test procedures, data interpretation and corrective action descriptions have been updated to improve clarity. In addition, expectations and responsibilities have been further defined, including:

Radiologist Section:

• Defined responsibilities of a CT protocol review and management team

• Clarified qualified medical physicist responsibilities

 Radiologic Technologist Section:

• Clarified expectation of action limits

• Updated water CT number and standard deviation (noise) testing procedure and data interpretation and corrective action sequences

• Updated artifact evaluation test procedure section

• Combined daily technologist quality control data form and weekly checklist into one form

• Removed standard-artifact free image section

 Qualified Medical Physicist Section (QMP):

• Revised review of clinical protocol section

• Updated the following sections:

• Radiation beam width recommended performance criteria and corrective action

• Low contrast performance data interpretation and analysis

• CT number accuracy recommended performance criteria and corrective action

• Artifact evaluation test procedure

• CT uniformity data interpretation and analysis, timeframe and corrective action

• CT scanner display calibration data interpretation and analysis and corrective action

• Removed the image thickness test: The vast majority of clinical CT scanners now use multidetector technology. With such scanners, image thickness is largely independent of data collection, except for the minimum image thickness available. Since image thickness is a computed quantity, it is no longer a failure mode for modern scanners. As such, it was decided that it is no longer necessary to include it as a required test within the ACR CT QC Manual. For the few single slice scanners still in use, it may be valuable for the QMP to verify both radiation beam width and image thickness, as the two are tied to each other and deficiencies may occur.

If a scanner does not pass a specification recommended by the ACR in their QC manual or a specification that the medical physicist designed, the test should first be repeated to confirm the result. Next, consult the vendor’s Technical Manual. If the same type of test is provided in the vendor’s technical manual, run the test as specified by the vendor and apply the vendor’s specification. If the vendor’s specification is passing and the clinical images do not have a clinically significant image quality issue, corrective action is likely not needed. If the vendor-provided test result is outside the vendor's specification, or there is believed to be a clinically significant degradation of image quality for the images used for diagnosis, service should be contacted.  

If the vendor does not provide specifications for a particular test, then the ACR or medical physicist’s test result should be benchmarked and monitored over time. Please note additional testing outside of the vendor specifications may not be supported by the manufacturer.

Communication is key in these instances. The QMP should not just perform a test and inform the site that a service call is required. The QMP has a responsibility to provide clear communication regarding the specific issue under discussion, what specific tests have been performed, what results have been observed and what specifications (e.g. manufacturer’s specifications) are being used to determine whether the system is in calibration.  

In some cases, a machine may pass all vendor specifications, but when the clinical protocol is applied to the ACR phantom, a failing result is obtained. Some elements of a clinical protocol, such as the reconstruction algorithm, may make assumptions that apply to human anatomy but may cause distortion in phantom images. For example, beam hardening or scatter corrections may perform differently in phantoms than in patient and distort CT numbers or lead to phantom artifacts. The hardness of the x-ray beam can also vary among scanner models, shifting CT numbers relative to non-vendor specifications. In addition, specifications that involve adaptive aspects of clinical protocols, such as iterative reconstruction or size-specific calibration files, can depend on precise interaction of phantom, test object, and protocol. Therefore, the use of absolute limits may not be as important as recording the consistency (constancy) of values over time.

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