Masahiro Ishine

A comparative study of attenuation correction algorithms in single photon emission computed tomography (SPECT)

A computer based simulation method was developed to assess the relative effectiveness and availability of various attenuation compensation algorithms in single photon emission computed tomography (SPECT). The effect of the nonuniformity of attenuation coefficient distribution in the body, the errors in determining a body contour and the statistical noise on reconstruction accuracy and the computation time in using the algorithms were studied. The algorithms were classified into three groups: precorrection, post correction and iterative correction methods. Furthermore, a hybrid method was devised by combining several methods. This study will be useful for understanding the characteristics, limitations and strengths of the algorithms and searching for a practical correction method for photon attenuation in SPECT.

Methods for measuring the renal uptake rate of 99mTc-dimercaptosuccinic acid (DMSA) : a comparative study

A comparative study of the renal uptake rate of99mTc-dimercaptosuccinic acid (DMSA) was performed using a phantom study and clinical data from 100 patients (200 kidneys) with a variety of renal diseases. The measurement methods for renal uptake rate studied here include a posterior-view method, a conjugate-view method, and a method using single photon emission computed tomography (SPECT). The renal uptake rates obtained by the posterior-view method significantly (P<0.001) depended on kidney depth correction. With the SPECT method, the cut-off level for delineating the kidney was changed according to the background count ratio using the results of the phantom study. The renal uptake rates obtained by the SPECT method correlated significantly (P<0.001) with those obtained by other methods, and there were no significant differences as compared with those obtained by the conjugate-view method. An analysis of error with the above methods indicated that the error relating to the sensitivity to body thickness was smallest for the SPECT method and greatest for the posterior-view method. In terms of measurement of renal uptake rate only, the conjugate-view method is considered the most useful because it needs no kidney depth correction and requires very little additional effort or examination time.

Electron beam intraoperative radiation therapy (EBIORT) for localized pancreatic carcinoma

Treatment results for 37 patients with localized pancreatic carcinoma treated using electron beam intraoperative radiation therapy (EBIORT) with curative intent from 1978 to 1990 in National Shikoku Cancer Center Hospital and the related hospitals were presented in comparison with those of a control group comprising 40 patients treated with no use of EBIORT. With additional treatment of EBIORT, 37 patients survived longer than the control 40 patients (p less than 0.05 during the 19th and 31st month). In the macroscopically total or partial resection, patients treated with EBIORT survived slightly longer than the controls. In the unresectable lesions, patients treated with EBIORT survived longer than the control patients (p less than 0.05 during the 7th month). In this group, there was one 5-year survivor who received EBIORT plus postoperative external radiation therapy (ERT) to the unresectable pancreatic head lesion but died 5 years later of massive bleeding from the duodenal ulcerations. Patients with unresectable carcinoma treated by EBIORT plus ERT survived longer than patients treated with EBIORT alone (p = 0.065). Pain relief was obtained in 95.0% of the unresectable patients with pain. Major adverse effects caused by irradiation were gastrointestinal troubles in five patients (leakage of choledochojejunostomy, gastric ulcerations, duodenal stenosis, gastric ulcerations and duodenal stenosis, duodenal perforation and ulcerations). EBIORT proved to be effective in the relief of serious pain and in the improvement of the survival of patients with localized pancreatic carcinoma.

Simulation and experimental study of respiratory motion effect on image quality of single photon emission computed tomography (SPECT)

The effect of respiratory motion on the image quality of single photon emission computed tomography (SPECT) was investigated by computer simulation and experimentation. In the computer simulation, the phantom was assumed to be cylindrical with a uniform background and a spherical cold or hot spot. To simulate respiratory motion, a cyclic linear motion parallel to the axis of rotation of a gamma camere was assumed. The contrast in the transaxial images was calculated for various respiratory amplitudes and its dependence on lesion size and object contrast was investigated. In the experiments, a moving phantom was used to simulate respiratory motion. The simulation and the experimenal results were in good agreement within the range of statistical error. The effect on the lesion detectability was investigated using receiver operating characteristics (ROC) analysis, and a method for correcting respiratory motion was devised.

Single photon emission computed tomography (SPELT) using N-isopropyl-p-(123I)iodoamphetamine (IMP) in the evaluation of patients with epileptic seizures

To evaluate the clinical usefulness of IMP SPECT in the diagnosis of epilepsy, 6 normals and 52 patients in the interictal phase were studied. Thirty min after an intravenous injection of 111 MBq IMP, SPECT was performed using a rotating gamma camera. Of 21 patients with simple partial seizures, a localized decrease of uptake was shown in 16, and an increase in 3. Topologically, these findings corresponded well to the ictal symptoms. Nine of 13 patients with localized epileptic EEG had a good correspondence between the findings on EEG and IMP SPELT. In 20 of 23 with complex partial seizures, the coronal images showed laterality of uptake in the temporal lobes, whereas the CT was normal in 14. However, these findings on IMP SPECT agreed with the EEG in the temporal leads in only 5 cases. Of 8 patients with primary generalized seizures, a diffuse cerebral decrease was shown in 3 of 4 patients with convulsive seizures (grand mal), and a normal uptake in 3 of 4 patients with non-convulsive seizures (petit mal). However, 2 patients showed a localized decrease, therefore, we determined that they suffered from partial seizures evolving to secondarily generalization. From these data, we concluded that IMP SPELT could be a useful method in the diagnosis of epilepsy.

A unified design algorithm of two-dimensional digital filters for radioisotope image processing

A unified design algorithm of two-dimensional digital filters for radioisotope image processing based on the Fourier-Bessel transform and the weighted least-squares method is described. The algorithm presented here can treat the various kinds of two-dimensional digital filters in a unified approach. Design examples are presented and several graphs are included to show the relationships between the design parameters as an aid in practical applications. The application of the method in radioisotope image processing is also presented. Several low-pass, Wiener and band-pass filters were designed using the method and applied to some clinical data in nuclear medicine including SPECT images. The digital filter design technique proposed here is considered to provide a powerful tool for extraction of additional qualitative information and improvement of the quality of nuclear medicine images both in research and in routine clinical work.

Early and Delayed I-123 Imp Spect in Epileptic Patients with Partial Seizures and Normal Ct

Forty-six epileptic patients with partial seizures and normal CT underwent 48 examinations of early and delayed SPECT using I-123 IMP in the interictal phase. One of them underwent a follow-up SPECT in a more stable state compared to the first SPECT. Another patient, with informed consent, underwent a follow-up SPECT in combination with pharmacologic activation with bemegride. Early SPECT was performed 30 minutes after an IMP Injection and delayed SPECT 4 to 4 1/2 hours later. Temporal changes in uptake pattern were visually classified into six types and compared with known patterns of SPECT uptake in relation to ischemic, hyperemic, and other changes. These were also correlated with the amount of epileptic activity seen on the EEG.

Individual renal function study using computed tomography.

Using computed tomography, the renal parenchymal volume and tissue-plasma ratio of contrast enhancement, with a bolus injection, were measured, and the latter measurement is believed to indicate regional renal function per unit of parenchymal volume. 67 studies were carried out on 50 patients, 17 of whom were examined pre- and postoperatively. Of these 50 patients, 27 had hydronephrosis, 6 had renovascular disease, 4 had pyelonephritis and the remaining 13 were control patients. The product of tissue-plasma ratio of contrast enhancement and the calculated renal parenchymal volume were found to be in good correlation with the individual renal function measured with 99mTc-dimercaptosuccinic acid and 131I-hippuran. Since this method is reproducible, the kidney being examined may be seen in more detail.

A method for computing the derivative of noisy time-activity curves and its application to radioisotope dynamic analysis

A method for computing the slope or the derivative of time-activity curves containing statistical fluctuations is described. The algorithm presented employs digital differentiation as a digital filter. In designing an effective differentiating filter the Chebyshev-type min-max method and Remez exchange algorithm are used to minimise the weighted Chebyshev error. The validity of this method has been investigated using computer-based Monte Carlo simulation. Renogram curve analysis is presented as an example of an application of this method to radioisotope dynamic analysis. The ratio of the bilateral slopes of the renograms second segments estimated using this method correlated well with the renal plasma flow ratio (r = 0.97, n = 16). The functional images of the slope of the renograms second segments have been constructed and ascertained to be clinically useful. This method is considered to provide a powerful tool for extraction of quantitative information both in research and in routine nuclear medicine clinical work, and may be useful in various other fields.

Monte Carlo estimates of absorbed dose rate in various tissues and organs

A computer program based on the Monte Carlo technique was developed for calculation of absorbed dose rate in various tissues and organs. The accuracy of the program was tested by reproducing Bergers values of the specific absorbed fractions for point isotropic sources in water, and a good agreement with those obtained by the moments method was found within an error of several percent. In comparing with experiment and other Monte Carlo results, good agreement was also obtained within the range of statistical error. The absorbed dose rate for an 123I, 124I, 125I, 126I and 99mTc point source and their specific dose constants in various tissues and organs were calculated using this program. This computer program has the mass energy absorption and attenuation coefficients for 69 tissues and organs as a database file, and can be extended to various radionuclides used in nuclear medicine by adding their nuclear data to the program.