Scattered photons can be a problem in transmission computed tomography (TCT) when employing an un... more Scattered photons can be a problem in transmission computed tomography (TCT) when employing an uncollimated transmission source. As an uncollimated transmission source can generate many scatter events in the transmission data, accurate scatter correction is necessary during transmission imaging. The aim of this study was to evaluate two scatter correction techniques which can be used with an uncollimated flood source
Transmission sources used for image attenuation correction, allowing image quantification, are co... more Transmission sources used for image attenuation correction, allowing image quantification, are collimated to reduce scatter. We propose the same effect can be achieved for an uncollimated source by increasing source to patient distance. The aim was to compare planar image performance characteristics and absorbed doses of uncollimated and collimated radioactive printed paper transmission sources. The scatter contribution to the uncollimated (⁹⁹m)Tc source data was evaluated for different combinations of detector phantom distance, detector source distance and phantom source distance. Measurements were performed by increasing the Lucite phantom thickness in 1cm steps to 20 cm. Spatial resolution, detection efficiency and entrance absorbed dose rate were measured for the uncollimated and collimated transmission source images. Results derived from the energy spectra, obtained with the uncollimated transmission source indicate that scatter contribution increases with decreasing detector source distance. The scatter component in the uncollimated transmission images (detector source distances ≥ 60 cm; phantom source distances ≥ 40 cm) was comparable to that obtained with collimated transmission images. Attenuation coefficients obtained compared well (0.168 cm⁻¹ vs. 0.171 cm⁻¹). The full widths at half maxima differed by less than 0.9 mm. The detection efficiency of the uncollimated source was 2.5 times higher than obtained with the collimated source. The entrance absorbed dose obtained from an uncollimated source was 3.75 times larger than that obtained from the collimated source. An uncollimated transmission source (detector source distance ≥ 60 cm) results in acceptable image characteristics and presents a low cost, low dose, high efficiency option for transmission imaging.
Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB), Jan 10, 2016
Accurate activity quantification is applied in radiation dosimetry. Planar images are important f... more Accurate activity quantification is applied in radiation dosimetry. Planar images are important for quantification of whole-body images, enabling assessment of biodistribution from radionuclide administrations. We evaluated the effect of tumour geometry on quantification accuracy of (123)I planar phantom studies, including various tumour sizes, tumour-liver distances and two tumour-background ratios. An in-house manufactured abdominal phantom was equipped with a liver, different size cylindrical tumours, and a rod for tumour-liver distance variation. The geometric mean method with scatter and attenuation corrections was used for image processing. Scatter and attenuation corrections were made using the triple energy window scatter correction technique and a printed transmission sheet source, respectively. Region definitions for tumour activity distribution compensated for the partial volume effect (PVE). Activity measured in the dose calibrator served as reference for determining qua...
PURPOSE In this study, we used Gafchromic™ film XR-QA2 and RT-QA2 to characterize the film energy... more PURPOSE In this study, we used Gafchromic™ film XR-QA2 and RT-QA2 to characterize the film energy response against various radionuclides. We introduce a neutron depletion theoretical model that can describe film response as a function of cumulated activity. The film response was investigated with respect to different backscatter media such as polystyrene, perspex, lead and corrugated fibreboard carton (CFC). The sensitivity of the two types of film to different energies was also studied. Lastly, a film stack method was tested to allow the user to obtain sequential, cumulative doses at different time points. METHODS Pieces of Gafchromic™ film XR-QA2 and RT-QA2 were exposed to Am-241, Cs-137, Tc-99m, and I-131 to obtain various cumulative activities. After 24 h, each film piece was digitized by scanning it with an Epson Perfection V330 flatbed scanner to obtain 48-bit RGB TIFF images. Afterwards, each image was processed with the Image J software package. The film response was fitted to a theoretically derived function based on the neutron depletion model and the Beer-Lambert Law and compared with an existing fitting function. Layers of the film were also placed together and irradiated with the above-mentioned radionuclides to investigate the possibility of increasing the sensitivity of the film as a dosimeter. The energy response of the two types of film was investigated by irradiating pieces of film with different photon energies. RESULTS The theoretical response model fits OD vs cumulative activity accurately. XR-QA2 film shows good energy film response by using CFC as a backscatter material when using radionuclides. From the results, it is also evident that XR-QA2 is more sensitive to low energy gamma rays than RT-QA2. Its OD sensitivity can be increased by 2 ± 0.2 when using a double layer film and by 2.8 ± 0.3 when using a triple-layer film. By using a film stack, the experimental time can be decreased by using the second-order polynomial relationship obtained to relate the stacked film data to the single film data. CONCLUSIONS The neutron depletion theoretical model is accurate and contains less free parameters than higher-order polynomial fits. The Gafchromic™ XR-QA2 film is also better to use in nuclear medicine because of its higher sensitivity. The sensitivity of the film as a dosimeter can also be increased by using multiple layers of film. Experiment times can also be decreased by using the film stack method.
Background Different gamma camera calibration factor (CF) geometries have been proposed to conver... more Background Different gamma camera calibration factor (CF) geometries have been proposed to convert SPECT data into units of activity concentration. However, no consensus has been reached on a standardised geometry. The CF is dependent on the selected geometry and is further affected by partial volume effects. This study investigated the effect of two CF geometries and their corresponding recovery coefficients (RCs) on the quantification accuracy of 177Lu SPECT images using Monte Carlo simulations. Methods The CF geometries investigated were (i) a radioactive-sphere surrounded by non-radioactive water (sphere-CF) and (ii) a cylindrical phantom uniformly filled with radioactive water (cylinder-CF). Recovery coefficients were obtained using the sphere-CF and cylinder-CF, yielding the sphere-RC and cylinder-RC values, respectively, for partial volume correction (PVC). The quantification accuracy was evaluated using four different-sized spheres (15.6–65.4 ml) and a kidney model with know...
Purpose Monte Carlo (MC) modelling techniques can assess the quantitative accuracy of both planar... more Purpose Monte Carlo (MC) modelling techniques can assess the quantitative accuracy of both planar and SPECT Nuclear Medicine images. It is essential to validate the MC code's capabilities in modelling a specific clinical gamma camera, for radionuclides of interest, before its use as a clinical image simulator. This study aimed to determine if the SIMIND MC code accurately simulates emission images measured with a Siemens Symbia™ T16 SPECT/CT system for I-123 with a LEHR and a ME collimator and for I-131 with a HE collimator. Methods The static and WB planar validation tests included extrinsic system energy pulse-height distributions (EPHDs), system sensitivity and system spatial resolution in air as well as a scatter medium. The SPECT validation test comprised the sensitivity from a simple geometry of a sphere in a cylindrical water-filled phantom. Results The system EPHDs compared well, with differences between measured and simulated primary photopeak FWHM values not exceeding ...
Purpose The quantitative accuracy of Nuclear Medicine images, acquired for both planar and SPECT ... more Purpose The quantitative accuracy of Nuclear Medicine images, acquired for both planar and SPECT studies, is influenced by the isotope-collimator combination as well as image corrections incorporated in the iterative reconstruction process. These factors can be investigated and optimised using Monte Carlo simulations. This study aimed to evaluate SPECT quantification accuracy for 123 I with both the low-energy high resolution (LEHR) and medium-energy (ME) collimators and 131 I with the high-energy (HE) collimator. Methods Simulated SPECT projection images were reconstructed using the OS-EM iterative algorithm, which was optimised for the number of updates, with appropriate corrections for scatter, attenuation and collimator detector response (CDR), including septal scatter and penetration compensation. An appropriate calibration factor (CF) was determined from four different source geometries (activity-filled: water-filled cylindrical phantom, sphere in water-filled (cold) cylindric...
The possible association of increased left ventricular ejection fraction (LVEF) in patients with ... more The possible association of increased left ventricular ejection fraction (LVEF) in patients with increased serum Ca(2+) was observed in our clinic. Six patients with confirmed primary hyperparathyroidism and hypercalcaemia were studied prospectively. Tc-99m sestamibi gated SPECT was done pre- and postoperatively. The LVEF was abnormally high in all the patients pre-operatively, i.e. above the normal reference range (47-61%) as used in our clinic. It decreased in all of them postoperatively, yet in only three patients to values within the normal range. This was associated with normalisation of the serum Ca(2+) values. The median of the pre-operative LVEF was 74% and postoperative it was 61.5%. The median difference was 9% with a 95% CI for the median difference for paired data (6; 26). This was statistically significant. Increased LVEF was not previously described as part of the clinical picture of primary hyperparathyroidism. The in vivo effect of chronic hypercalcaemia on LV pump f...
The use of Monte Carlo (MC) simulations in nuclear medicine is on the rise due to its usefulness ... more The use of Monte Carlo (MC) simulations in nuclear medicine is on the rise due to its usefulness in modelling many physical phenomena which are difficult or impossible to measure. To use MC for gamma camera image simulations, it is important to validate the simulated data with the measured data to ensure that what is simulated is a true representation of the physical system being modelled. Therefore, in this study, the SIMIND MC code for modelling a Siemens Symbia T dual head SPECT/CT gamma camera fitted with high energy all-purpose collimators (HEAP) was validated. The validation was done by acquiring and simulating certain NEMA stipulated performance measurements for 131I. These measured and simulated performance data were processed and the results compared. The FWHM and FWTM for the gamma camera for measured and simulated system spatial resolution were 14.4, 29.7 mm versus 13.9, 25.9 mm. System sensitivity performance measurements and simulation produced results of 49 cps/MBq and...
Scattered photons can be a problem in transmission computed tomography (TCT) when employing an un... more Scattered photons can be a problem in transmission computed tomography (TCT) when employing an uncollimated transmission source. As an uncollimated transmission source can generate many scatter events in the transmission data, accurate scatter correction is necessary during transmission imaging. The aim of this study was to evaluate two scatter correction techniques which can be used with an uncollimated flood source
Transmission sources used for image attenuation correction, allowing image quantification, are co... more Transmission sources used for image attenuation correction, allowing image quantification, are collimated to reduce scatter. We propose the same effect can be achieved for an uncollimated source by increasing source to patient distance. The aim was to compare planar image performance characteristics and absorbed doses of uncollimated and collimated radioactive printed paper transmission sources. The scatter contribution to the uncollimated (⁹⁹m)Tc source data was evaluated for different combinations of detector phantom distance, detector source distance and phantom source distance. Measurements were performed by increasing the Lucite phantom thickness in 1cm steps to 20 cm. Spatial resolution, detection efficiency and entrance absorbed dose rate were measured for the uncollimated and collimated transmission source images. Results derived from the energy spectra, obtained with the uncollimated transmission source indicate that scatter contribution increases with decreasing detector source distance. The scatter component in the uncollimated transmission images (detector source distances ≥ 60 cm; phantom source distances ≥ 40 cm) was comparable to that obtained with collimated transmission images. Attenuation coefficients obtained compared well (0.168 cm⁻¹ vs. 0.171 cm⁻¹). The full widths at half maxima differed by less than 0.9 mm. The detection efficiency of the uncollimated source was 2.5 times higher than obtained with the collimated source. The entrance absorbed dose obtained from an uncollimated source was 3.75 times larger than that obtained from the collimated source. An uncollimated transmission source (detector source distance ≥ 60 cm) results in acceptable image characteristics and presents a low cost, low dose, high efficiency option for transmission imaging.
Physica medica : PM : an international journal devoted to the applications of physics to medicine and biology : official journal of the Italian Association of Biomedical Physics (AIFB), Jan 10, 2016
Accurate activity quantification is applied in radiation dosimetry. Planar images are important f... more Accurate activity quantification is applied in radiation dosimetry. Planar images are important for quantification of whole-body images, enabling assessment of biodistribution from radionuclide administrations. We evaluated the effect of tumour geometry on quantification accuracy of (123)I planar phantom studies, including various tumour sizes, tumour-liver distances and two tumour-background ratios. An in-house manufactured abdominal phantom was equipped with a liver, different size cylindrical tumours, and a rod for tumour-liver distance variation. The geometric mean method with scatter and attenuation corrections was used for image processing. Scatter and attenuation corrections were made using the triple energy window scatter correction technique and a printed transmission sheet source, respectively. Region definitions for tumour activity distribution compensated for the partial volume effect (PVE). Activity measured in the dose calibrator served as reference for determining qua...
PURPOSE In this study, we used Gafchromic™ film XR-QA2 and RT-QA2 to characterize the film energy... more PURPOSE In this study, we used Gafchromic™ film XR-QA2 and RT-QA2 to characterize the film energy response against various radionuclides. We introduce a neutron depletion theoretical model that can describe film response as a function of cumulated activity. The film response was investigated with respect to different backscatter media such as polystyrene, perspex, lead and corrugated fibreboard carton (CFC). The sensitivity of the two types of film to different energies was also studied. Lastly, a film stack method was tested to allow the user to obtain sequential, cumulative doses at different time points. METHODS Pieces of Gafchromic™ film XR-QA2 and RT-QA2 were exposed to Am-241, Cs-137, Tc-99m, and I-131 to obtain various cumulative activities. After 24 h, each film piece was digitized by scanning it with an Epson Perfection V330 flatbed scanner to obtain 48-bit RGB TIFF images. Afterwards, each image was processed with the Image J software package. The film response was fitted to a theoretically derived function based on the neutron depletion model and the Beer-Lambert Law and compared with an existing fitting function. Layers of the film were also placed together and irradiated with the above-mentioned radionuclides to investigate the possibility of increasing the sensitivity of the film as a dosimeter. The energy response of the two types of film was investigated by irradiating pieces of film with different photon energies. RESULTS The theoretical response model fits OD vs cumulative activity accurately. XR-QA2 film shows good energy film response by using CFC as a backscatter material when using radionuclides. From the results, it is also evident that XR-QA2 is more sensitive to low energy gamma rays than RT-QA2. Its OD sensitivity can be increased by 2 ± 0.2 when using a double layer film and by 2.8 ± 0.3 when using a triple-layer film. By using a film stack, the experimental time can be decreased by using the second-order polynomial relationship obtained to relate the stacked film data to the single film data. CONCLUSIONS The neutron depletion theoretical model is accurate and contains less free parameters than higher-order polynomial fits. The Gafchromic™ XR-QA2 film is also better to use in nuclear medicine because of its higher sensitivity. The sensitivity of the film as a dosimeter can also be increased by using multiple layers of film. Experiment times can also be decreased by using the film stack method.
Background Different gamma camera calibration factor (CF) geometries have been proposed to conver... more Background Different gamma camera calibration factor (CF) geometries have been proposed to convert SPECT data into units of activity concentration. However, no consensus has been reached on a standardised geometry. The CF is dependent on the selected geometry and is further affected by partial volume effects. This study investigated the effect of two CF geometries and their corresponding recovery coefficients (RCs) on the quantification accuracy of 177Lu SPECT images using Monte Carlo simulations. Methods The CF geometries investigated were (i) a radioactive-sphere surrounded by non-radioactive water (sphere-CF) and (ii) a cylindrical phantom uniformly filled with radioactive water (cylinder-CF). Recovery coefficients were obtained using the sphere-CF and cylinder-CF, yielding the sphere-RC and cylinder-RC values, respectively, for partial volume correction (PVC). The quantification accuracy was evaluated using four different-sized spheres (15.6–65.4 ml) and a kidney model with know...
Purpose Monte Carlo (MC) modelling techniques can assess the quantitative accuracy of both planar... more Purpose Monte Carlo (MC) modelling techniques can assess the quantitative accuracy of both planar and SPECT Nuclear Medicine images. It is essential to validate the MC code's capabilities in modelling a specific clinical gamma camera, for radionuclides of interest, before its use as a clinical image simulator. This study aimed to determine if the SIMIND MC code accurately simulates emission images measured with a Siemens Symbia™ T16 SPECT/CT system for I-123 with a LEHR and a ME collimator and for I-131 with a HE collimator. Methods The static and WB planar validation tests included extrinsic system energy pulse-height distributions (EPHDs), system sensitivity and system spatial resolution in air as well as a scatter medium. The SPECT validation test comprised the sensitivity from a simple geometry of a sphere in a cylindrical water-filled phantom. Results The system EPHDs compared well, with differences between measured and simulated primary photopeak FWHM values not exceeding ...
Purpose The quantitative accuracy of Nuclear Medicine images, acquired for both planar and SPECT ... more Purpose The quantitative accuracy of Nuclear Medicine images, acquired for both planar and SPECT studies, is influenced by the isotope-collimator combination as well as image corrections incorporated in the iterative reconstruction process. These factors can be investigated and optimised using Monte Carlo simulations. This study aimed to evaluate SPECT quantification accuracy for 123 I with both the low-energy high resolution (LEHR) and medium-energy (ME) collimators and 131 I with the high-energy (HE) collimator. Methods Simulated SPECT projection images were reconstructed using the OS-EM iterative algorithm, which was optimised for the number of updates, with appropriate corrections for scatter, attenuation and collimator detector response (CDR), including septal scatter and penetration compensation. An appropriate calibration factor (CF) was determined from four different source geometries (activity-filled: water-filled cylindrical phantom, sphere in water-filled (cold) cylindric...
The possible association of increased left ventricular ejection fraction (LVEF) in patients with ... more The possible association of increased left ventricular ejection fraction (LVEF) in patients with increased serum Ca(2+) was observed in our clinic. Six patients with confirmed primary hyperparathyroidism and hypercalcaemia were studied prospectively. Tc-99m sestamibi gated SPECT was done pre- and postoperatively. The LVEF was abnormally high in all the patients pre-operatively, i.e. above the normal reference range (47-61%) as used in our clinic. It decreased in all of them postoperatively, yet in only three patients to values within the normal range. This was associated with normalisation of the serum Ca(2+) values. The median of the pre-operative LVEF was 74% and postoperative it was 61.5%. The median difference was 9% with a 95% CI for the median difference for paired data (6; 26). This was statistically significant. Increased LVEF was not previously described as part of the clinical picture of primary hyperparathyroidism. The in vivo effect of chronic hypercalcaemia on LV pump f...
The use of Monte Carlo (MC) simulations in nuclear medicine is on the rise due to its usefulness ... more The use of Monte Carlo (MC) simulations in nuclear medicine is on the rise due to its usefulness in modelling many physical phenomena which are difficult or impossible to measure. To use MC for gamma camera image simulations, it is important to validate the simulated data with the measured data to ensure that what is simulated is a true representation of the physical system being modelled. Therefore, in this study, the SIMIND MC code for modelling a Siemens Symbia T dual head SPECT/CT gamma camera fitted with high energy all-purpose collimators (HEAP) was validated. The validation was done by acquiring and simulating certain NEMA stipulated performance measurements for 131I. These measured and simulated performance data were processed and the results compared. The FWHM and FWTM for the gamma camera for measured and simulated system spatial resolution were 14.4, 29.7 mm versus 13.9, 25.9 mm. System sensitivity performance measurements and simulation produced results of 49 cps/MBq and...
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