Contamination, a Major Problem in Nuclear Medicine Imaging: How to Investigate, Handle, and Avoid It

DISCUSSION

Contamination can be categorized as either directly patient-related, such as contamination of the clothing or hair, or indirectly patient-related, such as contamination of the patient’s surroundings (camera detectors, floors, sink, dustbins). Patient contamination can be identified easily during image acquisition, but because surrounding contamination cannot be so easily identified, daily wipe tests are mandatory (2).

Interpretation of a nuclear scan can be affected by many kinds of technical errors during its acquisition, as well as by injection artifacts, prosthetic implants, patient motion, and extracorporeal contamination such as that of the patient’s clothes, the table, or the collimator (1). The possibility of false-positive results due to technical errors or contamination should always be kept in mind, especially if the lesions are prominent in a single projection (3).

Contamination of the detector or collimator usually involves a limited area and appears as a line throughout whole-body images (3). Detector contamination differs from direct patient contamination; in the latter, the location of the radiotracer changes with movement of the patient, whereas in the former, the location remains static. In our case, the observed contamination of the collimators was suspected to be due to urinary spillage during the direct radionuclide cystogram that had been performed just before the bone scan.

Patient motion is also a common source of artifacts in images but usually can easily be detected by cine displays, sinograms, and summed planar images. To avoid any discomfort-induced motion artifacts, the technologist should ensure that the patient is comfortably positioned during the image acquisition. If needed, an arm support, holding straps, and sandbags may also be used to reduce patient movement during the acquisition (4).

Care should be taken to avoid contamination and other artifacts, as they interrupt the workflow of nuclear medicine technologists and physicians (because of the time needed for cleaning and decontamination) and expose patients to additional radiation (because of the need to repeat the imaging study).