This paper presents a high-speed pulse fluoroscopic x-ray generation system with high-voltage semiconductor hybrid switching modules to obtain a short fall time on the tube-voltage. The high-voltage semiconductor hybrid switching module consists of a super-cascade MOSFET switching circuit with a subordinate driving mechanism that has a mis-operation prevention strategy and voltage-dividing elements. The most significant features of the high-voltage semiconductor switch-type high-speed fluoroscopic system are its long life, freedom from maintenance, and compact size compared with conventional vacuum-tube systems. In this paper, tube-voltage fall waveforms are also discussed and evaluated based on two x-ray load models, a constant-current load model and an equivalent-resistance load model. Finally, tube voltage and fluorescence intensity, surface, transit, and scattered dose rates are examined to demonstrate the feasibility of using high-voltage semiconductor switching modules in a fluoroscopic x-ray generation system.
Temporal subtraction images are obtained by the subtraction of a previous image from a current image. We investigated the detection of simulated lesions and also performed a recognition task in interstitial lung diseases using CR(computed radiography)images and temporal subtraction images. Five types of lung lesions, namely, ground-glass, reticular(#1 and #2), honeycomb, and micro-nodule patterns were simulated. Each simulated lesion was superimposed on one of the left lung, right lung, or mediastinum. Chest phantom images without and with simulated lesions were radiographed as previous and current images, respectively. Seventy-five CR and temporal subtraction images for each independent condition were used for evaluation. Five radiologists subjectively evaluated the detection and recognition of simulated lesions on CR images and temporal subtraction images. The results showed that the detection and recognition of simulated interstitial lung lesions on temporal subtraction images was significantly improved compared with CR images. Furthermore, the high detection rate was obtained with temporal subtraction images regardless of the subtlety and location of simulated lesions.
A complex subtraction method was developed to accurately measure modulation transfer functions(MTFs)in positive and negative frequencies of magnetic resonance images(MRI). The MTF was calculated from the line spread function, which was obtained with an original phantom by a process of subtraction of the complex images. The MTF in conventional spin-echo(SE)and Turbo SE, in which effective echo time was set at the first echo, were evaluated by changing the T_2 of the phantom in the frequency-and phase-encoding directions. MTFs indicated the characteristics of the k-space trajectory for each pulse sequence. Using this method, the influences of image nonuniformity and unnecessary artifacts could be eliminated. Analysis of the MTF with the complex subtraction method made it possible to obtain more detail regarding the resolution properties of MRI.
To investigate optimal iteration times and the number of subsets on OSEM(ordered subsets expectation maximization), we estimated the values of the target-to-background ratio(T/B), signal-to-noise ratio(S/N), and NMSE(normalized mean square error). We acquired SPECT data with four scan durations, 5, 10, 15, and 20 min, using a three-headed SPECT scanner(GCA-9300 A/UI, Toshiba Co., Ltd.), and reconstructed the OSEM algorithm varying iteration and subset numbers. We determined the optimal values of T/B, S/N, and NMSE for OSEM, and compared these by filtered back projection(FBP). We observed the same convergence propotity between OSEM and FBP. We evaluated this by comparing it with the FBP method to obtain the most appropriate parameter from 36 kinds of SPECT images. In the spherical hot spot phantom study, the values of 2 and 15 were optimum for iteration times and number of subsets, respectively.
In order to use the ordered subsets expectation maximization(OSEM)algorithm for reconstruction of myocardial gated SPECT using ^<99m>Tc myocardial agents, we evaluated the optimal reconstruction parameters in phantom and clinical studies. Since processing time increases in proportion to iteration number, as few iteration numbers as possible is desirable. From the results of left ventricular(LV)volume and normalized mean square error(NMSE)in the phantom study, we concluded that the optimal number of iterations and subsets were 2 and 15, respectively, and the most suitable cutoff frequency of the Butterworth filter was 0.438 cycles/cm. LV volume estimated using the OSEM algorithm was less than that using the filtered back projection(FBP)algorithm. In the clinical study, the correlation coefficients of end-diastolic volume(EDV), end-systolic volume(ESV), and ejection fraction(EF)estimated by the OSEM algorithm were 0.99(p<0.001), 0.97(P<0.001), and 0.96(p<0.001), respectively. A strong correlation was observed between the results of the two methods.
In the evaluation of osteopenia, Singh's index and other methods employing a plain roentgenogram have been utilized, all of which are readily accessible without expensive equipment. We developed a new method for quantifying radiographic osteopenia using hip plain roentgenography, and we have evaluated its utility by comparing it with dual-energy x-ray absorptiometry(DXA). The subjects were 231 women aged 40-91 years who had undergone plain hip joint roentgenography and hip DXA. X-ray films showing femoral neck fracture or deformity or external rotation of the hip joint were not included in this study. Osteopenia was quantified by counting the number of principal compressive trabeculae in the left femoral neck using a magnifying glass. Thickness and photographic density of the cortex in the femoral head were used as references when selecting the trabeculae, i.e., trabeculae thinner or fainter than the cortex were not counted. The results of trabecular counting were significantly correlated with bone mineral content and density by hip DXA. Among the parameters of hip DXA, femoral neck BMD showed the highest correlation with trabecular number, and the correlation was higher when counting in the larger region of the femoral neck. The results suggest the potential utility of our method for estimating hip BMD.
We developed a method of CT scanning with different gantry angles(tilted CT). Examining five patients with bronchogenic carcinoma, the tilted CT method seemed to be useful to show the relationship between nodules and vessel involvement, especially involved branched vessels. In addition, the tilted CT method more clearly showed the pleural indentation of interlobar fissures. The tilted CT method appears to be useful in evaluating pulmonary nodules as an additional technique to conventional CT scanning.