The Radiation Dose Measurement And Research Of CT And DSA

ObjectiveAccording to compare the differences between predictive value of radiation dose and actual measured value displayed by Spiral CT and DSA equipment during exposuring,we evaluate the accuracy of predictive value of radiation dose showed by various diagnostic radiology units respectively and find the reason and law causing differences between the actual measured value and predictive value. By changing the scanning parameters, to verify and analyze the impact on radiation dose showed by spiral CT and DSA equipment. Materials and Methods1. Three spiral CT were GE Prospeed II,GE Lightspeed 16 and GE Lightspeed VCT 64. Instruments used for measuring the radiation dose were solidose400 type dosimeter, pen-type ionization chamber(length 100mm),a cylindrical head mold made by PMMA material(diameter 16cm) and a phantom(diameter 32cm). When measuring spiral CT dose index, ionization chambers were placed in the center hole and four surrounding holes of head mold and the phantom respectively, mold center axis overlaps with the central axis of the gantry, head mold is placed on the head position of scanner table, phantom is placed on the scanner table, accompany with 360 degree rotation, they make scanning measurement under different scanning parameters respectively, recording indicates dose showed by the scanner.2. Three DSA devices were Philips FD20, GE LCE+ and Siemens Artis FA1250 m A. Instruments used for measuring were Solidose400 type dosimeter, Doseguard 100 kerma area product meter and a cylindrical phantom made of PMMA material(thickness 20cm).According to the GB9706.23-2005/IEC60601 to determine interventional reference point(IRP): Medical examination bed( height 90cm), SID=100cm. Probe is placed under the phantom 15 cm away from the isocenter.To record reference dose and actual measured dose respectively at different scanning parameters and analysis them. Results1. when other parameters were determined, the change of slice thickness has no effect on CT scanning dose index; Tube voltage is in direct proportion to CT dose; A linear positive correlation between tube current and CT dose; The diameter is inversely proportional to the CT dose; CT dose decreases as the increase of mold body’s radial depth; Pitch varies inversely as radiation doses, at the same time increased pitch adds to the additional doses of ultra-imaging range; Collimation varies directly as dose; Radiation field and algorithm have no effect on CT dose; Using tube current modulation techniques can reduce the CT dose in the premise of ensuring image quality. The difference between indicates dose showed by CT machine and actual measured value is relevant to pitch: when the pitch is greater than 1, the difference is negative; when the pitch is less than 1, the difference is a positive number, and the smaller the pitch, the greater the difference.2. There exist great differences between predictive value of DSA system radiation dose and measurements,regardless of spot film or perspective. Conclusion1. There are many ways to reduce the doses received by subjects, such as by reducing the tube voltage, reducing the tube current, increasing the pitch, increasing the width of the collimator, reducing scanning conditions of body thin subjects, using tube current modulation techniques, and so on.2. When make dosimetry evaluation of CT and DSA, calculating an effective dose of a subject can not rely on equipment predictive value absolutely.