In this report, we analyzed the field factors for the 10 MV X-ray irregular fields using a linear accelerator. We compared the field factors and TMRs at the same depth for two irregular fields of the same shape by means of (1) lead blocks and (2) installed multi-leaf collimator. There were no significant differences in either of the TMRs, and the TMRS were in good agreement with the TMR regarding their equivalent square field. On the other hand, there were significant differences in both the field factors, and the field factor for the lead block irregular fields were greater. From the results of this experiment, we are of the opinion that in routine dose calcultion, it is better to use field factors for the open fields in the case of the lead block irregular fields, and to use field factors for the equivalent square fields in the case of the irregular fields by means of multi-leaf collimator.
CSF dynamics were analysed in 17 children with subdural effusion or with hydrocephalus using radionuclide cisternography and X-CT with metrizamide in order to compare the results obtained using the two methods. Count rates and densities in ROIs set on the cisterna magna, basal cistern, parasagittal region and lateral ventricle were recorded at 3 hours, 6 hours, 24 hours and 48 hours after intrathecal administration of 0.5〜1mCi ^111In DTPA for radionuclide cisternography and 170 mgI/ml metrizamide for X-CT with metrizamide respectively. Serial images of radionuclide cisternography were found to be useful and satisfactory for detecting reflux. On the other hand, serial X-CT with metrizamide was beneficial for clarifying the pathophysiology of CSF circulation with accurate monophologic definition. We concluded that a combination of radionuclide cisternography and X-CT with metrizamide was necessary for accurate examination to evaluate CSF circulatory disturbance.
Orthopantomograph Model OP-3 (Siemens) has sliding transitions (a continuously moving X-ray beam rotation center) between the anterior and lateral X-ray beam rotation centers. In Orthopantomograph Model OP-3, about 60 percent of the image layer is reproduced during these sliding transitions. We have considered formulae for the position of the X-ray beam rotation center and for the ratio between the angular velocity of the film in relation to the beam and the angular velocity of the beam in relation to the object, during sliding transition, by analyzing the mechanism of the sliding transition. Consequently, the whole image layer included during sliding transition for Orthopantomograph Model OP-3 was able to be calculate utilizing our formulae.
Modulation transfer function (MTF) of the tomography was measured by the slit method and the both sides of the slit were shaved to an angle of 45 degrees. MTF was expressed by a three-dimensional display which has been described in our previous paper, as a function of the distance from the object plane. Moreover, the area of the MTF was calculated and was plotted as a function of the distance from the object plane. We analyzed the blurred images made with hypocyclodial, circular and zonographic motions by use of these methods. It is concluded that the three-dimensional display and the area curve were very useful for expressing the MTF of the tomography and for its analysis.
The evaluation of experimental results should be based on the experimental design along with due consideration given to experimental errors. We found the value of the errors and introduced into image evaluation the analysis of variance method, which is one of statistical methods effective for error evaluation. Our present experiment has been made on : (1) The effect of the medium speed intensifying screen and spatial frequency regarding the M.T.F. ; and (2) The effect of the developing temperature and density on the R.M.S. granularity. We discussed the results with the use of the statistical method in contrast with not using it.
Since October 1984, we have developed the"Chest-holder", a novel positioning device for the chest radiography, especially of great benefit for patients with difficulty in standing in an upright position. It consists of three parts holding-pads, supporting rods, and a simultaneous adjuster. This device enables the hospital technicians to easily attain the appropriate position of the patient, thereby reducing patient-assistance and X-ray exposure to the radiographic technicians. Furthermore, it was demonstrated that the "Chest-holder"was even useful regarding radiography for normal subjects as it provided great savings in the setup time.