Technical note: an evaluation of a Diamentor based system for estimation of spot film dose-area product values

Balancing patient dose and image quality

The formation of images in diagnostic radiology involves a complex interdependence of many factors. The ideal balance is to obtain an image which is adequate for the clinical purpose with the minimum radiation dose. Factors which affect radiation dose and image quality can be grouped under three headings; radiation quality, photon fluence and removal of scattered radiation. If optimal performance is to be achieved, it is necessary to understand how these factors influence image formation and affect radiation dose, and apply methodology for image quality and dose analysis at each stage in the development and use of X-ray equipment.

Automatic system for measuring dose-area product (DAP) in ROI fluoroscopy

A computerized system for monitoring dose-area product (DAP) has been developed for region of interest (ROI) fluoroscopy in which patient exposure is reduced using an x-ray attenuating filter with an aperture. The system includes an IBM compatible computer which is connected through an IEEE-488 interface to an electrometer which measures the charge from a DAP ionization chamber. A digital input/output board connects the computer to the filter placement device to determine whether the filter is in or out of the beam, and to the x-ray generator to determine when the exposure is due to spot filming. The computer logs the DAP from conventional fluoroscopy, ROI fluoroscopy and spot filming separately, applying the appropriate calibration factor for each. Measured DAPs, fluoroscopic DAP rates and exposure times are displayed in real-time. The system has been installed in a GI fluoroscopic room so that the dose-reduction potential of ROI imaging can be evaluated.

Patient dose measurements from femoral angiography

Investigation of patient dose from femoral angiography requires detailed logging of dose-area product (DAP) measurements, which is time-consuming and only possible on small numbers of patients. A simple model for the femoral angiogram study consists of two regions; lower limbs and torso. The experimental phantom was the abdominal and pelvic sections of a Rando phantom, and two 10 cm diameter water filled cylinders to represent a lower limb. DAP rate during screening, and the DAP per spot film exposure were obtained in two rooms. Total DAP values were measured on 100 patients in each room. The median screening time and number of spot film exposures were divided between the two regions. The DAP from screening and spot films for each region was estimated by combining the phantom and patient data. The total DAP predicted by the model agreed to within 7% of the median DAP from the patient studies Conversion to effective dose gave 9.0 mSv for the newer room compared with 2.8 mSv for the older room. In the newer room it was estimated that digital spot film exposure contributed 88% of the total effective dose. In the same room, exposure of the torso contributed 98% of the total effective dose. The model will enable interpretation of total DAP measurements made from femoral angiogram studies without the need for detailed DAP measurements on every patient. Attempts to reduce patient dose from femoral angiography must concentrate on reduction of the number and dose per exposure from abdominal and pelvic digital spot films.