Nuclear medicine physicians use so-called gamma cameras for myocardial perfusion scintigraphy. The devices record radioactive substances that are injected into the patient and show changes in the heart muscle (myocardium). Now a new gamma camera is able to record images faster and by using much less radiation.
Currently, only eleven of these types of devices are being used in hospitals and physician offices in Germany. We spoke with Prof Wolfgang Burchert from the Heart and Diabetes Center (HDZ) NRW in Bad Oeynhausen about the advantages this technology offers both patients and physicians.
Prof Burchert, recently the HDZ NRW offered physicians the use of a new generation gamma camera. What makes this device so special?
Wolfgang Burchert: The Discovery NM 530 c gamma camera by GE Healthcare features new detectors and a novel imaging geometry to create tomographic images. This results in a four to five-fold increase in sensitivity, thus cutting the recording time and the amount of injected radioactive perfusion markers in half.
This means the radiation exposure is only half that of a conventional gamma camera. Since image recording generally only takes five minutes, fewer involuntary patient movements are recorded, which prevents image blurring. Everyone is familiar with this effect from using a regular photo camera – when you overexpose film to too much light – and objects and people blur with fast motion.
For which types of exams is this device being used at the HDZ?
Burchert: This camera is specifically optimized for myocardial perfusion scintigraphy, which illustrates the blood flow to the heart muscle after physical or pharmacological stress. The camera records the patient’s heart three-dimensionally. The computer reconstructs and illustrates the data in cross-sectional images. This process shows the poorly perfused areas of the heart muscle under stress. These poorly perfused – ischemic – parts of the heart muscle should subsequently be supplied with stents or bypasses as part of an effective treatment of the patient’s coronary heart disease.
What other concrete advantages does this new technology offer patients?
Burchert: The device is not an enclosed ring of detectors; instead, the camera detectors are positioned in a recording head that is approximately 25cm in size and roughly covers a 90-degree segment. The camera is pulled up near the patient’s heart. The device does not move during image recording. Conventional gamma cameras rotate around the patient to subsequently reconstruct the different views tomographically. Since the new camera is set up to where it continuously captures three-dimensional images, it does not need to be moved. This process improves patient acceptance far more than enclosed systems, which make many patients feel confined.
How does the gamma camera impact or make the nuclear medicine physician’s job easier?
Burchert: The technology saves the physician time and subsequently provides economic advantages. You can also generate all relevant data simultaneously by using a one-time setup. The main advantage is the brief examination time. The high level of patient acceptance also makes our job as physicians somewhat easier.
What technology is behind the faster images with a lower radiation dose?
Burchert: The new gamma camera includes so-called CZT (cadmium-zinc-telluride) detectors. These are semiconductor detectors in the form of square crystals, which are subdivided into pixel detectors. This creates multiple measuring channels that facilitate great signal detection over a wider area. These detectors work similarly to the chips in a modern digital camera. Here the light is directly converted into an electrical impulse, which in turn creates the individual pixels that compose the image. The gamma camera practically features an analog mode of operation, yet the electromagnetic radiation in the new gamma camera exhibits significantly higher energy. The use of the semiconductor detectors eliminates the typical need for photomultiplier tubes. This allows for a considerably more compact construction of the camera head.
The second advantage is the so-called multi-pinhole technology, which makes it possible to record the entire detector area at the same time. You could have the gamma camera continuously acquire data for ten minutes for example and then reconstruct a volume between minute two and seven from the collected data. The recording time can, therefore, be shortened or extended. In addition, an ECG signal is being recorded. This way, we can measure the individual cardiac activity phases and derive cardiac functional parameters that are of special prognostic significance for the patient. As a result, the technology is overall very comprehensive and trendsetting.
I take from this that you are very satisfied with this device.
Burchert: It definitely represents significant progress. Yet with all things, there are also a few minor quirks. The camera – since it features a specific imaging geometry – depends on the heart being exactly positioned in the center of the exposure field. Software is used for positioning control in this instance. In individual cases, this alignment process proves more difficult. This is currently the only critical issue, I can see. Apart from that, this technology predominantly offers advantages.