Solid state detectors in nuclear medicine.

Since Nuclear Medicine diagnostic applications are growing fast, room temperature semiconductor detectors such CdTe and CdZnTe either in the form of single detectors or as segmented monolithic detectors have been investigated aiming to replace the NaI scintillator. These detectors have inherently better energy resolution that scintillators coupled to photodiodes or photomultiplier tubes leading to compact imaging systems with higher spatial resolution and enhanced contrast. Advantages and disadvantages of CdTe and CdZnTe detectors in imaging systems are discussed and efforts to develop semiconductor-based planar and tomographic cameras as well as nuclear probes are presented.     

Radiation dosimetry in nuclear medicine.

Radionuclides are used in nuclear medicine in a variety of diagnostic and therapeutic procedures. A knowledge of the radiation dose received by different organs in the body is essential to an evaluation of the risks and benefits of any procedure. In this paper, current methods for internal dosimetry are reviewed, as they are applied in nuclear medicine. Particularly, the Medical Internal Radiation Dose (MIRD) system for dosimetry is explained, and many of its published resources discussed. Available models representing individuals of different age and gender, including those representing the pregnant woman are described; current trends in establishing models for individual patients are also evaluated. The proper design of kinetic studies for establishing radiation doses for radiopharmaceuticals is discussed. An overview of how to use information obtained in a dosimetry study, including that of the effective dose equivalent (ICRP 30) and effective dose (ICRP 60), is given. Current trends and issues in internal dosimetry, including the calculation of patient-specific doses and in the use of small scale and microdosimetry techniques, are also reviewed.     

Radiation protection programs in nuclear medicine

The development of radiation protection programs in nuclear medicine has been stimulated by the greater degree of regulation that exists in this form of medical imaging. A program within an institution will depend on the amount and type of work to be undertaken, the resources available, and the commitment of the individuals involved. These factors may be part of a licensing program or exist within a broader framework. General policy may be set forth in a manual or guidelines distributed to all employees. The continuing review and development of policy is the function of the institutional committee on radiation. This review must consider patients and workers with the objective of reducing overall dose while obtaining the maximum amount of clinical information. The responsibility for radiation protection is shared by the institution, the licensee, and the individual employee.     

Radiation dose to the hands in nuclear medicine

Study of the distribution of radiation dose across both hands during the dispensing and administration of radiopharmaceuticals is useful in the assessment of the extremity doses received by nuclear medicine personnel. Some staff in the UK have already been designated as classified radiation workers due to the radiation doses that their hands may receive. With possible forthcoming reductions in the dose limits, it is important that as much data as possible is available on such dosimetry. By measuring the dose at nine different locations on each hand, an optimal site (the base of the second digit) to represent a more accurate 'mean hand dose' could be determined. The use of inserting different butterfly cannula into a vein, prior to radiopharmaceutical administration, was assessed in terms of the dose reduction effect to the member of staff performing the task. It was found that a long tubing cannula (300 mm) did not significantly reduce the radiation dose of the operator whereas shorter ones (95 mm) gave a very significant dose reduction.     

Radiation exposure and dosimetry in transplant patients due to nuclear medicine studies.

Organ transplantation is now an accepted method of therapy for treating patients with end stage failure of kidneys, liver, heart or lung. Nuclear Medicine may provide functional data and semi-quantitative parameters. However, one serious factor that hampers the use of nuclear medicine procedures in transplant patients is the general clinical concern about radiation exposure to the patient. This leads us to discuss the effective doses and radiation dosimetry associated with radionuclide procedures used in the management and follow-up of transplant patients. A simple way to place the risk associated with Nuclear Medicine studies in an appropriate context is to compare the dose with that received from a more familiar source of exposure such as from a diagnostic X-ray procedure. The radiation dose for the different radiopharmaceuticals used to study transplant organ function ranges between 0.1 and 5.3 mSv which is comparable to X-ray procedures with the exception of 201Tl and 111In-antimyosin. Thus Nuclear Medicine studies do not bear a higher radiation risk than the often used X-ray studies in transplant patients.     

Radiation management for infectious waste from nuclear medicine studies

An industrial waste management service has refused to collect medical waste from our hospital owing to radioactive contamination found in the waste in July 2000. An investigation revealed that the "three-way stopcock" and handling diapers used for radioisotope examination were the radioactive contaminants. We therefore reconsidered the system of medical waste maintenance especially for radioactive materials. Since February 2001, we have resumed radiation maintenance by following the manual for the handling diapers of patients administered radiopharmaceuticals issued by five organizations associated with JRS, JSRT, JSNM, JSNMT, and JARPM. A major change was to check the radioactive waste at the individual departments and at a centralized check system. This eliminated the problem of dumping radioactive material into medical waste as well as resolving the concerns of the industrial waste management service.     

Workflow in nuclear medicine.

This paper discusses a workflow management system for nuclear medicine. It augments the more conventional PACS with automatic transfer of studies along the chain of activities making up an examination in nuclear medicine. A prototype system has been designed, built, and installed in a department of nuclear medicine, active in a network of hospitals.     

Radiation protection for the parent and child in diagnostic nuclear medicine

Conclusions The assessment of the radiation risks involved in the administration of radiopharmaceuticals to parents and children must be based wherever possible on direct measurements and realistic estimations of the doses involved. The data presented in some of the publications on which this editorial is based can be used to estimate the doses to members of the public and to hospital staff from a range of nuclear medicine procedures and under circumstances other than those discussed above. However, in the current climate of raised risks associated with radiation and an increasing public awareness, further dosimetric data are required to rectify the existing deficiencies and to keep pace with future expansion and developments in the application of nuclear medicine to the investigation of parents and children.It is prudent to issue general recommendations based on worst case values of radiation doses, and these can be estimated more easily from separate observations of such factors as dose rate, distance and time, rather than from measurements of integral dose. Practitioners of nuclear medicine are in the best position to obtain the missing information highlighted above, particularly the biokinetic data. In some instances, acquisition of such information has revealed a lower risk than previously considered. It remains to be seen how the new annual limits and recommendations from the ICRP will be implemented by regulatory authorities. However, this information is essential to permit a realistic assessment of the impact of future changes in radiation protection legislation.     

Radiation dose rates from adult patients undergoing nuclear medicine investigations

Adult patients undergoing nuclear medicine investigations may subsequently come into close contact with members of the public and hospital staff. In order to expand the available dosimetry and derive appropriate recommendations, dose rates were measured at 0.1, 0.5 and 1.0 m from 80 adult patients just before they left the nuclear medicine department after undergoing one of eight 99Tcm studies, an 123I thyroid, an 111In leucocyte or a 201Tl cardiac scan. The maximum departure dose rates at these distances of 150, 30 and 7.3 microSv h-1 were greater than those found in similar published studies of adult and paediatric patients. To limit the dose to an infant to less than 1 mSv, an 111In leucocyte scan is the only investigation for which it may be necessary to restrict close contact between the infant and a radioactive parent, depending on the dose rate near the surface of the patient, the parent's habits and how fretful is the infant. It is unlikely that a ward nurse will receive a dose of 60 microSv in a working day if caring for just one radioactive adult patient, unless the patient is classified as totally helpless and has undergone a 99Tcm marrow, bone or brain scan. The data and revised calculations of effective exposure times based on a total close contact time of 9 h in every 24 h period should allow worst case estimates of radiation dose to be made and recommendations to be formulated for other circumstances, including any future legislative changes in dose limits or derived levels.     

Emergency nuclear medicine.

Despite the widespread clinical acceptance of new imaging modalities in the evaluation of acutely ill patients, there are still a number of applications for radionuclide scintigraphy. The unique ability of tracers to evaluate organ function or localized tissue dysfunction often can provide more useful information than strictly anatomic imaging modalities. Although the ventilation-perfusion study probably remains the dominant emergency procedure in most nuclear medicine laboratories, other procedures, such as those described herein, play an important role and should be available for acutely injured or ill patients.     

Pulmonary nuclear medicine.

This article reviews the contribution made by nuclear imaging to the assessment, diagnosis and monitoring of patients with respiratory disease. It focuses on several specific areas including the diagnosis of pulmonary embolism, the investigation of intrapulmonary infection and neoplasm and the role of positron emission tomography (PET) scanning.