Diagnostic applications of Medical Physics

Diagnostic imaging procedures are based on well-known principles of physics. The role of the Department of Medical Physics is to ensure that all the components of equipment function according to their specifications. It ensures that the patient receives the best cost-effective service and that the procedures used are safe for both patients and personnel. New techniques and computer assisted procedures are also introduced and evaluated.

1. Nuclear Medicine

In the Department of Nuclear Medicine radio nuclides (radio-isotopes) are used to diagnose disease. In most cases the distribution of the isotope through the body after application is observed by means of a scintillation camera. This allows the clinical evaluation of physiological function or anatomy of organ systems for diagnosis of disease. We also work in close co-operation with, especially, the Cardiology and Hematology Departments. Non-imaging procedures are also performed to evaluate organ function of for example the thyroid and kidneys.

1.1. Rendering of service

An extremely important aspect of the contribution of medical physicists in the Department of Nuclear Medicine is to perform quality control of equipment. The procedures used are based on internationally recognised methods. The equipment includes scintillation cameras, radiation detectors, gamma and beta radiation counters, automatic film processors and radiation dosimeters. The sensitivity of the quality control programme is such that it is possible to detect and rectify a problem in respect of the equipment before it affects the clinical images. This serves to ensure that examinations are carried out optimally in all respects, and that patient reports leaving the department are of the highest quality. Quality control is mainly of a preventative nature, but is also important after a breakdown or replacement of old spare parts to ensure that the equipment has been repaired to comply with set standards.

The department also prepares specifications for the purchase and manufacturing of new equipment. Since the cost of this kind of equipment is very high, thorough planning for efficient functioning of the equipment are essential if cost-effectiveness is to be ensured. This service is also offered to private companies.

In the Department of Nuclear Medicine a variety of pharmaceutical compounds labelled with radionuclides are used to diagnose disease. This includes the diagnosis of diseases of organs such as the heart, lungs, liver, kidneys, brain and spleen. Quality control of radio-pharmaceutical preparations administered to patients is closely associated with quality control in respect of equipment. The binding of the radionuclide to a specific compound using a labelling kit, as well as the purity of certain preparations is checked on a daily basis, serving, on the one hand, to guarantee the quality of examinations and, on the other hand, to rule out the possibility of subjecting the patient to unnecessary radiation risks.

In certain cases the physicist is personally responsible for performing a diagnostic radionuclide investigation, in which case he reports on the specific study together with the physician. His special knowledge of the physical aspects of the investigation, that is the limitations as well as the positive features of the equipment, is of extreme importance to ensure that patients receive the best possible care.

We as medical physicists are principally responsible for the development and extension of new and existing computer programs. Scintillation cameras are linked to computers for acquisition and processing of clinical images. Successful program development ensures that the time for investigations are minimised. This avoids patient discomfort and it improves patient throughput and productivity. The medical physicists in the Medical Physics Department have a thorough knowledge of the functioning of a specific computer system and are capable of grasping problems quickly under pressure and offering a workable solution.

Radiation monitoring of patients and personnel constitutes a further aspect of the duties of the Medical Physics Department. Routine monitoring of personnel classified as radiation workers is mainly carried out by means of thermo luminescent dosimetry. The amount of radiation to which a person has been exposed over a specific period of time can be determined and, if necessary, recommendations can be made to restrict such exposure to a minimum. Radiation exposure to patients during clinical investigations is determined by extensive measurements and calculation.

The Medical Physics Department is involved in projects during which other departments use radio nuclide techniques, for instance to determine the influence of medication on certain physiological conditions. These projects are often in collaboration with the Anesthesiology and Pharmacology Departments.

1.2. Research

We briefly refer to the most important research projects currently undertaken by this department.

1.2.1. Improvement of imaging techniques involving radio nuclides

Following the injection of organ-specific radio-active compounds, images are obtained by means of a scintillation camera. These images are used by physicians to diagnose abnormal organ function. The quality of images can be improved by means of computer assisted image processing techniques. The main aim of this research is to correct for scattered radiation, distance dependent resolution and attenuation of radiation with computer assisted techniques.

Radio nuclide images are not only employed for the purpose of visualisation, but also to determine the distribution of radio nuclide compounds and the volume of organs accurately. Quantification renders it possible to determine the function of organs such as the heart and kidneys more accurately. The information is used to develop mathematical programs that predict the distribution of the tracer within the body. The models are not only important for the purpose of physiological assessment of function, but also for the correct calculation of the radiation dose administered to patients.

1.2.2. Collection and processing of data by means of a personal computer

We have already referred to the important role played by the use of computers in nuclear medicine. Because of the high cost involved in the purchase and maintenance of proprietary computer software and systems, a search was launched for a cost-effective alternative that would meet the specifications of existing systems. Since personal computers are so readily available, it was decided to make this the point of departure of the research. A project is therefore underway to develop software to interface scintillation cameras to personal computers for the acquisition of image data. This project has already progressed to the point where certain studies can be acquired by means of the personal computer. The acquisition program however requires further refining for the ultimate purpose to be used for all clinical Nuclear Medicine investigations.

1.2.3. Development of radiopharmaceutical preparations

Radio pharmaceutical preparations are generally freely available and often locally produced. In a few cases the cost of imported labelling components is high. In order to effect savings for patients some of these preparations are manufactured in house. Active research with a view to extending and, where possible, improving the range is under way.

1. 2.4. Development of new agents for palliative treatment

Primary mammary and prostate carcinoma often spread to skeletal bone. Bone metastases are an extremely painful condition. Existing treatment methods for relieving pain of metastases include external beam radiation, but the side-effects of such treatment are often unsatisfactory. Radio-nuclides labelled with bone- seeking compounds can also be used for palliative treatment of metastasis. In co-operation with the Departments of Nuclear Medicine, Oncotherapy and Chemistry, rhenium labelled compounds are being developed. These compounds have both therapeutic and imaging characteristics. Once successful labeling is possible, the preparation will be tested and eventually used to treat this group of cancer patients to relieve pain.

1.2.5. Research support and consultation

The Department of Medical Physics is operating an imaging system in the animal facility of the Faculty of Medicine for use in its own research, as well as for use by other departments. Imaging of the distribution of radio nuclide compounds and calculation of the associated radiation dose is made possible by the use of this system. The facility is, for instance, employed to develop new clinical investigation procedures and to evaluate new medication. In co-operation with the Department of Haematology, the effectiveness of new anti-clotting medication is being evaluated by studying their effect on blood platelets labelled with radio nuclides.

2. Diagnostic Radiology

2.1. Rendering of services

In diagnostic radiology X-ray studies are performed for diagnostic purposes. There is some risk associated with the use of X-rays for patients as well as personnel; therefore the medical physicists of the Department of Medical Physics are responsible for the radiation safety where radiation is used. This responsibility involves the checking of X-ray equipment in order to ensure that safety requirements are met, as well as regular quality control of the equipment concerned. This quality control ensures that the radiation to which a patient is exposed during diagnostic X-ray examinations is restricted to a minimum. Moreover this quality control of X-ray equipment also results in cost-saving.

Specialised X-ray equipment is used for the early diagnosis of breast cancer in women. For the early diagnosis of cancer extremely fine detail is recorded on X-ray film. It is the function of the medical physicist to assist in optimising image quality and radiation exposure to patients. The procedures used for the chemical development of the X-ray film during the examination is also critical. Consequently, quality control of the X-ray equipment as well as the film processing are done on a regular basis and according to a fixed prescribed protocol.

In contrast to the conventional two-dimensional planar X-ray film examinations, computed tomography (CT) and magnetic resonance imaging (MRI) are used for diagnostic investigations to produce three dimensional image information. Magnetic resonance enables the radiologist to obtain clinical information concerning the patient in a non-invasive manner by using radio frequency electromagnetic waves and a strong magnetic field. An MRI scanner is extremely expensive and sophisticated.

Since medical physicists have a thorough knowledge of computers and the physical principles on which the equipment is based, they play a valuable supporting role regarding the use of computer assisted equipment such as with X-ray computed tomography and magnetic resonance imaging. In these, powerful computers and sophisticated mathematical methods are used for the reconstruction of clinical images. Regular quality control guarantees the optimal functioning of the equipment and ensures that correct diagnoses can be made.

2.2. Research

The use of computer-assisted procedures for planar imaging and tomography has improved the efficiency of diagnostic procedures performed in Radiology.. The Department of Medical Physics is involved in a research programme aimed at the development of an affordable computer-assisted procedure for the acquisition and transmission of diagnostic images. Existing images can be acquired by means of a scanner or video camera linked to a personal computer and stored on the disk of the computer. The computer software that has been developed, enables the user to display and manipulate the images. A further facility is the possibility of transmitting images by telephone to other users who are then able to display them by means of a personal computer. The one problem which researchers need to bridge is that of the time involved in the transmission of the images. It has already been mastered to a large extent through image compression using mathematical algorithms. The compressed data can then be transmitted using a telephone line and decompressed once received. The essential requirement is that the algorithms must be such that image information is not lost. We are investigating image quality after images have been decompressed.

The above-mentioned project offers significant applications in health care. Using this system, physicians in outlying areas can, for instance, transmit images to other centres for a second opinion or expert advice. In addition, the system can also to a certain extent contribute towards improved image display, because it offers the facility of changing the contrast of the image to suit user preference.

Diagnostic radiology is an established and vital part of health care and we will play an increasingly important role to provide health care of a high quality and to be part of a team to research new procedures and equipment.