New approach for attenuation correction in SPECT images, using linear optimization

Photon attenuation as an inevitable physical phenomenon influences on the diagnostic information of SPECT images and results to errors in accuracy of quantitative measurements. This can be corrected via different physical or mathematical approaches. As the correction equation in mathematical approaches is nonlinear, in this study a new method of linearization called 'Piece Wise Linearization' [PWL] is introduced and to substantiate its validity for SPECT image reconstructions, a phantom study is performed. A SPECT scan of a homemade heart phantom filled with 2 mCi 99mTc was acquired by dual head Siemens E.Cam gamma camera equipped with LEHR collimator. Row data of the scan were transferred in DICOM format to a pc computer for reconstruction of the images using MLEM iterative algorithm in Matlab software. Attenuation map of the phantom micro [chi] were derived using PWL with linear optimization approach. Based on that, the attenuation corrected SPECT image of the phantom were reconstructed and compared with non-corrected image, using MLEM iterative algorithm. Comparison of the corrected and non-corrected images confirmed with CT attenuation correction method. Attenuation correction in SPECT image can be achieved successfully, using emission data and piecewise linearization with linear optimization approach. The corrected image of f[chi] and attenuation map micro[chi] of the heart phantom using this approach promise acceptable image quality for diagnostic clinical use

survey of annual effective and genetically significant dose from conventional X-ray examinations in 10 counties Khorasan province-Iran

A study has been conducted to assess two useful radiation protection indices, the annual per-capita effective dose equivalent [AED] andthe genetically significant dose [GSD], from conventional diagnostic radiography in 10 counties with more than 1,886,000 inhabitants in Khorasan province in Iran. The health centre authorities of Khorasan province were asked to record data of their patients [sex, age, weight and height] who had undergone radiography during one month starting October 2002, with the radiography specifications [kVp, mAs, FSD, field size] and conditions of the X-ray machines [filtration, model and performance]. Based on the gonad absorbed dose level, the radiography data were first divided into 5 groups. Then, the average gonad and effective dose of the radiography groups were estimated using ODS-60 software, and finally, GSD and AED of each county were calculated. Average number of radiography per thousand inhabitant was 34.5 in this study, which varied from 9.4 [Kashmar] to 109.4 [Ferdos]. Number of X-ray units per 1000 population was 0.008. The GSD and AED of inhabitants in 10 counties in Khorasan province is 0.012 and 0.014 mGy/y/person respectively. The GSD and AED of 10 counties in Khorasan province were much lower than those in most of other countries, which would have been due to lower number of X-ray units and examinations per 1000 inhabitants. Although this would reduce the risk of radiation absorbed dose from medical diagnostic, but it also showed need to improve and expand the health care facility and services in those cities

Estimation of radiation absorbed dose of aircrew in domestic flights

Cosmic radiations from outer space are continuously exposing the earth. Ambient dose rate at the atmosphere, apart from unusually and transient solar activities, is mostly a function of latitude and altitude. At aircraft altitude and temperate latitudes, it increases by a factor of 20-25. Therefore, aircrew and frequent flyers are exposed to high levels of cosmic radiation. This paper considers general radiation protection aspects of cosmic radiation exposure to aircrew in domestic flights in Iran. Ambient dose rate in several domestic flights was measured using survey meter model RDS-110. Based on the measured data and duration of the flight, the effective doses of the aircrew were calculated and compared with that derived from radiation transport codes of CARI-6 introduced by Civil Aerospace Medical Institute, Oklahoma City, USA. Due to good agreement between measured and calculated values, the CARI-6 program was used to determine the dose rates in different altitude throughout the country to provide a simple algorithm for calculating route dose in domestic flights. Equivalent dose rate in domestic flight's altitude can be calculated from, a[h]b where h is the altitude in thousand feet; a and b are constants depending to geographic location. Based on the equivalent dose rate and the flight profile; simple algorithm provided to estimate the route dose in any domestic flights. The annual dose limit of general population allows the aircrew to spend 290 hour in 27-33 thousand feet altitude in domestic flights; therefore, only female aircrew should be made aware of the need to control doses during pregnancy

[Study of wedge factor dependence with depth, field size and SSD in [60] Co units]

In radiotherapy, wedge filters are used to modify iso-dose curves and hence optimize tumor dose distribution in patient. To deliver prescribed dose, timer or monitor unit should be involved the dose with no wedged field and wedge factor. Therefore, any variation of wedge factor due to treatment parameters will affect the deliver dose to patients. Effects of field size, SSD and depth of treatment on wedge factor were studied, using universal wedge filters with nominal angles of 30°, 45° and 60°, a hand made water phantom 21x21x10 Cm and a 0.6 cc Farmer ionizing chamber, at different SSD and depth from the water surface. Wedge factors were calculated as the ratio of charge [nC] of the wedge to open beam, measured by and an electrometer model NE2571, while the dosimeter was irradiated for 60s with Picker ATC9 [60]Co unit. Except for 60° wedge filter, with 95% certainty, there is no meaningful relation between wfs with field size and depth. For 60° wedge filter, variation of wf for situation used in this study is about 0.55% per Cm'Cm variation in field size and 0.28% per Cm variation in depth. An inverse linear relation between wf and SSD approved with 95% certainty. Variations of wf for 30°, 45° and 60° wedge filters, for situation used in this study are 0.11%, 0.18% and 0.33% per Cm variation in SSD respectively. Dependence of wfs to FS, depth and SSD for 60o wedge filter were formulated and shows that the field size and depth of treatment has a negligible effect on wedge factor. Correction of wf for SSD, which has a large domain of variation, is appreciable in clinical usage [more than 5%] and for 60o wedge filter can be calculated as: wfc=wf [1- 0.0033[SSD-80]] 65