caesium-iodide scintillators coupled to flat-panel detectors drives digital imaging

Biomedical imaging has come a long way since 1895. A 100 years plus have passed since x-rays have been discovered and used to help diagnose problems of the body. During this range in time, man has grown to use x-rays with better data collecting media. Gone are the days of film plates and darkrooms.

The transmission and detection of X-rays still lies at the heart of radiography, angiography, fluoroscopy and conventional mammography examinations. However, traditional film-based scanners are gradually being replaced by digital systems that are based primarily on caesium-iodide scintillators coupled to flat-panel detectors. Some systems rely on charged-coupled devices (CCD) rather than flat panels but the end result is the same: the data can be viewed, moved and stored without a single piece of film ever being exposed.

The humble X-ray also forms the heart of modern computed tomography (CT) systems, which can obtain a series of 2D “slices” through the body. A whole host of other physics-based techniques or “modalities” are also routinely used to look inside the body without the need for a scalpel. Single photon emission CT (SPECT) and positron emission tomography (PET) rely on the properties of radioactive isotopes, while magnetic resonance imaging (MRI) exploits the well known principles of nuclear magnetic resonance (NMR), and is the starting point for functional MRI (fMRI). Last but by no means least, ultrasound uses high-frequency sound waves in a similar manner to submarine sonar to produce images of tissue and blood vessels.

Common sense tells us that the more data we collect the more information we would have to make an intelligent conclusion for the problem at hand. This isn’t necessarily true. Sometimes there is too much data. This is a problem with multislice CT technology.

The problem of data overload is only going to get worse according to Sébastien Ourselin, project leader for medical imaging and a member of the e-Health team at CSIRO Telecommunications and Industrial Physics in Epping, Australia. “The issue will not be with the quality of data,” says Ourselin. “Rather, the question will be ‘How can I extract the information that is relevant to me from these hundreds of megabytes of data in just one or two minutes so that I can make a clinical diagnosis?’. Can you expect a radiologist to wait two hours to get a good segmentation of a heart?”

Andrew Todd-Pokropek, head of the medical-physics department at University College London, believes that time would be saved if medical physicists could ensure that all the data leaving the scanner were usable. “There should be ways of controlling data acquisition during the scan to optimize the quality of the data produced,” he says. Todd-Pokropek would like to see “intelligent acquisition” systems that allow for the effects of patient motion. Indeed, even if patients remain absolutely still while being scanned, a beating heart or the movements associated with breathing can sometimes distort the final images.

The multislice CT technology is an awesome tool for imaging cancer tumors, heart function, lung function, and anuerisms to name a few. The multislice scanner captures many images of the target from different angles. Usually the patient is lying still, for roughly 20 minutes, while the camera is positioned over the target area. Then the camera takes its pictures and rotates around the patients body to get pictures of the target from another angle. Rotation movements are from 5 to 10 degrees covering a 120 to 180 degree arc. (Based on my own experiences with the procedure.) The captured images are collected and analyzed by a computer. The result is a very detailed graphical report that only the technician and doctor can read.

Some anomaly readings do get in the collection, due to the patient moving (sneezing, coughing, scratching that itch, etc.), and the result can be effected by them. This is where there is a need for processes to increase the quality of the data. Engineers are looking at combining the strengths of multislice CT and PET technologies.

There are three options for generating a combined PET/CT scan according to Todd-Pokropek. The first is to collect the PET and CT images independently and then morph them together with powerful image-registration software. This is relatively straightforward for brain scans, but more difficult for whole-body scans. The second option involves fixing the patient to a bed and then wheeling them into the scanners in quick succession. However, it is quite a challenge to design a bed that will restrict the motion of patients to within a millimetre. The third option is to literally bolt the two scanners together in a single system. This last option has found favour with the major medical-imaging manufacturers, all of whom now market such systems.

“Multimodality image fusion is the future of nuclear medicine,” says Todd-Pokropek. “It is absolutely critical that imaging data from nuclear medicine is combined with that from other modalities to extract the most information.” Indeed, Todd-Pokropek predicts that PET/CT scanners will eventually replace single PET systems. This would be part of a general move towards blending physiological information with the anatomical information provided by traditional, diagnostic images.

Other combinations are being looked at as well, for example, fMRI and electroencephalogram (EEG), for studying brain activity. The difficulties in making these hybrid technologies work is in the software programming. According to the article, great minded people are needed to build the hardware and software that will work with it. If any of you are looking for a career change, I can assure you that this will not be boring.

Source: PhysicsWeb.org