By John Garrett
It is common knowledge that medical imaging by X-ray is moving to 100 percent digital detectors. There are a large number of hospitals converting CR, and a few film, to DR due to reimbursement being lowered for institutions that do not have digital detectors. The idea behind the change is to provide all patients with the latest technology and the best images possible. The best images being part of the best care possible. What about nuclear medicine?
There have been digital nuclear medicine detectors in service since 1997. They have been used in a number of specialty applications including cardiac cameras and women’s health. Yet the digital detectors are still a niche item. But to understand why all nuclear medicine cameras are not yet digital detectors, there are a number of factors to consider.
The most common studies performed by nuclear medicine cameras are functional heart tests that measure how the heart works while looking for damaged tissue. Typically by circling the patient with two detectors, a three dimensional reconstruction is created and measured. This is called Single Photon Emission Computed Tomography (SPECT). Radioactive isotopes that have been injected into the patient send gamma photons into the sodium iodide crystal face on the camera detector causing it to glow. This faint quick glow is amplified by vacuum tubes called Photo Multiplier Tubes (PMT) and that electronic signal is deciphered into an image via computer. The image is created by a computer and easily made into a DICOM compliant format.
The technology of nuclear medicine is well understood. There have been improvements in the various parts that make up the nuclear medicine camera, but the technology is basically the same as it has always been. The exceptions are the digital detectors that were previously mentioned.
The question is, why are nuclear medicine cameras still using vacuum tubes instead of being digital? The technology of the flat detectors works well enough, the current problem lies in physics. The digital detectors themselves generate a great deal of heat and require robust cooling solutions. This has limited the practical size of the detector to date. To create larger detectors, the heat increase is geometric in nature. The ability to cool larger detectors is not practical with the current technology. The original detectors were designed for satellites to monitor radiation on the Earth. In space, cooling is not a challenge.
Will nuclear medicine cameras move to all digital? With technology developments moving at the current rate the answer is “maybe.” It is entirely possible that the same move to digital will happen in the nuclear medicine world. If a cooling solution, or a lower heat detector is created, it is likely. However, it is also possible that new imaging technology will make nuclear medicine as a field obsolete.
John Garrett has 20 years experience in imaging service including general radiation, mammography, CT and nuclear medicine. He has worked for third-party service companies, manufacturers, sales companies and in-house imaging teams. Currently, he is manager of clinical engineering at Catholic Health Initiatives.