Graphic noise properties are usually evaluated using the Wiener spectrum. However, this approach is not appropriate for periodic noise for two reasons. One is that it takes infinite values at the spatial frequencies of periodic noise. The other is that when adopting a numerical integration, it allows unstable values at each spatial frequency, depending on the integral region. Introducing three types of spectra (W₁, W₂, and W₃) in connection with the Wiener spectrum, we propose a practical approach to evaluation of periodic noise. Graphic images sometimes contain noise that is not totally random and not perfectly periodic. Therefore, using the Wiener spectrum and the W1 spectrum, we also propose two factors for evaluation of the degree of randomperiodicity of noise containing periodic signals.

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The Japan Society of Medical Physics (JSMP) has published a new dosimetry protocol “JSMP-01” for the calibration of radiotherapy beams. This protocol provides a new definition of the calibration point (depth) in order to obtain the absorbed dose at a reference point (D_r) by the calculation in high energy electron beams. This study evaluated the difference in the absorbed dose at the depth dose maximum (D_dmax) and D_r calculated from the absorbed dose at the calibration point. Further, the difference in the absorbed dose (D_dmax) at “measured maximum depth (d_max)” was evaluated using “temporary maximum depth (d_max). ” In the experiment at a depth interval of 0.1 g cm2, no difference was observed between (D_dmax) and (D_r). However, in the experiment at a depth interval of 0.3 g cm-2 the differences between (D_dmax) and (D_r) increased to 6.4%and 5.2% at 4 MeV and 6 MeV, respectively. Subsequently, at all energy levels the difference between (D_dmax) and (D_r) of all energy was more than 3% at a depth interval of 0.4 g cm^-2. The differences between (D_dmax) and (D_dmax). were 2.68% and 4.50% at 6MeV and 9 MeV, respectively, for this depth interval.

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Purpose: This work was aimed at quantification of lactate concentration using proton MR spectroscopy (MRS). We carried out a basic study to clarify the characteristics of signal change and T2 relaxation time of lactate that occur by J coupling in point resolved spectroscopy (PRESS) sequence.
Materials and Methods: Proton MRS was done for a water phantom containing 10mmol/L creatine and lactate on a clinical 1.5 T MR system by using an asymmetric PRESS sequence. The coupling constant J was 7.35 Hz. In acquisitions, TE was varied from 68 ms up to 544 ms, with an increment of 68 ms (1/2J) and TR was fixed to 10000 ms.
Resul ts: The shape and signal intensity of the lactate signal vary depending on its phase. The lactate signal intensity at TE 272 ms was higher than at TE 136 ms despite the longer TE. T2 relaxation times of lactate in the negative in-phase (TE 136ms, TE 408 ms) and positive in-phase (TE 272 ms, TE 544 ms) were 1033 ms and 1042 ms, respectively (no significant differences), so that when the same phase was used, regardless of the phase condition, T2 relaxation behavior was not different. We considered that our results included over expression and loss of lactate signal depending on the phase.
Conclusions: For evaluation of the lactate peak, we recommend the use of the positive in-phase signal because it is larger than the negative in-phase signal. The influence of the asymmetric PRESS sequence, which may cause loss and over expression of lactate signal, should be considered in the calculation of the quantification. The T2 relaxation time should be also considered in the calculation of the lactate value since it affects the value considerably.

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A Japanese code of practice for clinical dosimetry, titled “Standard Dosimetry of Absorbed Dose in External Beam Radiotherapy” was published by the Japan Society of Medical Physics (JSMP) in 2002. It mostly followed IAEA Technical Reports Series No.398, which was based on N_D,W,i.e., the calibration factor in terms of absorbed dose to water for a dosimeter. The Japanese primary standard dosimetry laboratory, however, has not supplied N_D,W but N_X, as the calibration factor in terms of exposure. The unique feature of the Japanese code was provision of a data table of calculated conversion factors, N_D,W / N_X values, for many types of ionization chambers, excluding new plane-parallel ionization chambers. This paper describes the experimental evaluation of the conversion factors for the new plane-parallel ionization chambers, such as the Roos-type and Advanced Markus chambers. The obtained N_D,W / N_X values for PTW 34001, Wellhöfier PPC 40 and PTW 34045 were 37.96 ± 0.19,37.85 ± 0.36 and 37.90 ± 0.26 (Gy/C kg^-1), respectively. They agreed with estimations based on Monte Carlo calculations.

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