Quality control

Quality Control (QC) tests are an important part of the nuclear medicine routine work. They should be performed at designated time intervals to maintain proper functionality of the gamma camera. QC is a constituent part of the nuclear medicine’s department quality management program. A list of tests involved in QC for gamma camera and CT follows. Guidelines on the procedures of QC should be available to all the technologists who perform these tests.

Constancy tests: those tests performed to determine variations to reference data, which describe the equipment, its individual components, and initial state. These are performed by the equipment’s operator.

Acceptance tests: assert that the equipment’s performance parameters satisfy technical, legal, and/or manufacturer specifications. These are performed by the equipment’s manufacturer.

Action levels: values used in constancy tests. If those values are exceeded, an investigation must be conducted according to the quality management framework.

Tolerance limits: if these are exceeded, the use of the equipment in the clinical routine is limited or possibly not allowed. Violations of tolerance limits, their causes and consequences must be documented and justified by the radiation protection officer.

Record keeping: documentation of QC procedures and results should be recorded, along with the date and the initials of the person performing the test.

Gamma Camera: Single Photon Emission Computed Tomography (SPECT and SPECT/CT)

D - Daily, W/M - Weekly/monthly, M – Monthly, Q - Quarterly

Daily tests

Visual and physical inspection of the SPECT gamma camera should detect external mechanical or electrical defects or damages. A touch pad test should be performed on a daily basis and after each collimator change. An additional operational check should be performed on emergency stop buttons, if available, which should light and shut-down all motor-driven system movements when pressed.

As shown in Figure 1, the window setting for the radionuclide to be used should be performed, for example ^99mTc, to ensure that the peak for the selected radiopharmaceutical coincides with the object under the camera. If this is not performed, degradation of the image quality and loss of spatial resolution may result.

Figure 1. Energy window setting for ^99mTc

Operational check of the background count rates with or without collimators and within one or more energy windows should be performed daily to detect radiation caused by possible radioactive contamination of the scintillation camera or surroundings, external radiation from a neighbouring unshielded source or an excess of electronic noise.

Extrinsic uniformity of the imaging equipment should be performed daily in order to access the system’s response to spatially uniform flux of ^99mTc, ⁵⁷Co or ¹⁵³Gd photons. Such a flood field uniformity may be tested qualitatively by visual inspection or quantitatively by calculation of the integral and differential image uniformity within camera’s central field of view (CFOV) and useful field of view (UFOV). Figure 2 demonstrates an example of extrinsic uniformity using ⁵⁷Co, which is an external flood source.