The Correlative Study On Image Quality, Concentration Of Iodinated Contrast Material And Radiation Dose

PurposeTo investigate the relationship among the x-ray image quality, and radiation dose and concentration of iodinated contrast materials in order to look for the optimized radiographic parameters of X-rays exposure to the patients, and to conclude a math formula to describe the relationship between body-thickness and X-ray tube voltage(kVp), which enable to prevent the patients from deterministic effects and the stochastic effects due to over-exposured dose, and the damage to the human body caused by higher iodine concentration under the direction of such formula.Material and methodsThe x-ray digital subtraction angiography (DSA) was simulated using a phantom made of acrylic acids, which consists of 10 to 25 acrylic blocks. The effect of the X-ray exposure doses and iodine concentration of contrast materials on the image quality acquired, and effect of the kVp on doses absorbed by the patients and iodine concentration were observed through changing the radiographic parameters( i.e., kVp and mAs) to find the optimized parameters for minimizing the iodine concentration and lowing the dosage absorbed by the patients under such circumstances.25 parts of 30cm×30cm× 1.0cm were made using poly acrylic acid blocks which can freely be assembled to simulate the corresponding to the studied part of the human body according to the different thickness of various parts ofthe body. 25 groups (each contains two cylindrical vessels) of cylinder vessel (referred to as vessels) were drilled parallelly and horizontally on one of the blocks, which will be inserted into the phantom. The vessel is 1.2 mm in diameter and 40 mm in length drilled along its mid-plane at intervals of 11 mm apart. The vessels were filled with iodinated contrast which is geometric proportional distribution to resemble to the blood vessel filled with different concentration of contrast medium. Then four different thicknesses of phantom were combined (i.e., 10 cm, 15 cm, 20 cm, and 25 cm in thickness), and surface dose of X-ray image intensifier(XII) was set at 1.0 uGy/frame, 1.5 uGy/frame. 2.0 uGy/frame, 2.5uGy/frame, 3.0 uGy/frame, and 4.0 uGy/frame respectively to each phantom. X-ray images were obtained with different exposure combination of the kVp and mAs under each surface dose of Ⅻ. At the same time, relative exposure parameters were recorded, and the actual radiation doses of both Ⅻ and phantom were measured. The images obtained were evaluated with ROC method and the data acquired were processed, and presentation about the relationship between the thickness of phantom and optimized kVp was established eventually. Results1. When the thickness of phantom is 10 cm, 15cm and 20cm respectively, the dose input to the surface of Ⅻ is 1.0μGy/frame. When the thickness of phantom is 25 cm and the dose is 1.5μGy/frame with acceptable image quality for the diagnosis. After 1.5 uGy/frame, the numbers of vessel were increased no longer with the input dose increased.2. Fifty percent of vessels visualized (namely, vessel group 13) was taken as the threshold for detecting iodine concentration with 14.12 mg I/ml. If minimum energy imparted to the patients was assigned as the criterion of corresponding to kVp, the presentation of relationship between body thickness and optimized kVp was kVP = 64 + 0.89 *D (D is the thickness of the body).