Energy window optimization for Y-90 Bremsstrahlung SPECT imaging: A Monte Carlo simulation study

Introduction: Detection of scattered photons in photo-peak window degrades image contrast and quantitative accuracy of single-photon emission computed tomography (SPECT) imaging. Increases image contrast lead to significant improvement of image quality. The triple energy window (TEW) method, which has developed to eliminate the counts of scatter photons in measured counts, was applied to I-111 SPECT study and its effect was examined in a simulation study. Materials and method: The Siemens SYMBIA gamma camera equipped with a medium energy (ME) collimator was simulated by the Simulating Medical Imaging Nuclear Detectors (SIMIND) program. We used the SIMIND Monte Carlo program to generate the I-111 SPECT projection data of the Jaszczak phantom. The phantom consists of six spheres with different diameters (9.5, 12.7, 19.1, 15.9, 25.4, and 31.8 mm) which are used to evaluate the image contrast. Geometric, scatter and penetration fraction and also, point-spread functions (PSFs) and contrast curves were drawn and compared. Results: Results showed that 171keV photo-peak compared to 245keV gave the best results with a ME collimator when the TEW scatter correction method was applied. This can be explained by the large amount of collimator scatter and penetration from the photo-peak and by the collimator for 245 photo-peak window. Conclusion: With TEW scatter correction method, it is better to use a 171keV photo-peak window because of the better spatial resolution and image contrast.

123I Produced by 124Te(p, 2n)123I reaction is contaminated with 124I (less than 5%) and 126I (less than 0.3%). High energy photons from these mixed radioiodine compromise seriously image quality due to scattered photons and to septal penetration in the collimator. Four collimators of LEAP (for low energy all purpose), LEHR (for low energy high resolution), MESI (for medium energy made by Siemens) and MENU (for medium energy made by nuclear technology) mounted on a rotating gamma camera (Siemens, ZLC-7500), were examined in order to select a suitable collimator for 123I SPECT (single photon emission computed tomography) imaging. Sensitivities were measured with a plane source (5 X 5 X 0.5 cm) at the collimator face and distances from 2 to 30 cm in air. And, spatial resolutions in FWHM (full width at half maximum) and FWTM (full width at tenth maximum) were determined from line spread functions with planar and SPECT imaging. From the comparison of collimator performances with 99mTc and 123I, both collimators for low energy were not useful for 123I imaging. In other two collimators for medium energy, however, apparently the effect of septal penetration by the higher energy photons were also recognized, MENU with high geometrical resolution was more suitable for 123I SPECT imaging compared with MESI. And, it is important to perform the SPECT imaging with radius as short as possible.

Introduction: Treatment efficacy of radiation therapy using Yttrium-90 radionuclide is evaluated by the bremsstrahlung SPECT imaging following radiation therapy. The radioisotopic images have the ability to provide reliable activity map of 90Y distribution. But these images have a low quantitative accuracy in the 90Y bremsstrahlung SPECT imaging, therefore the optimization of some imaging important indicators i.e. the energy window width and collimator geometry, which heavily affect acquisition images quality, is necessary. The aim of this paper is to estimate the effects of the energy window width and the hole diameter of a ME collimator on the image contrast of the 90Y bremsstrahlung SPECT images obtained using SIMIND Monte Carlo simulation program and improve image quality which could be used to estimate activity distribution after radiation therapy. Materials and Methods: In this paper we simulated the SPECT system and a Jaszczak phantom consist of six hot spheres in different diameters by use of the SIMIND Monte Carlo simulation program to study 90Y SPECT images by assessment of the holes diameter of a ME collimator including 2.35, 2.59, 2.82, 2.94, 3.06 and 3.3 mm with fixed values of the collimator and septa thicknesses (3.2 cm and 1.14mm, respectively) in the two energy windows including 60- 160 keV and 60-400 keV. SPECT imaging protocol is selected according to the clinical study. An activity of 1.5GBq 90Y was considered for the hot spheres without background activity. We used OS-EM algorithm to reconstruct projections and evaluated the contrast of the reconstructed images of six hot spheres of Jaszczak phantom with selection of proper ROIs. Results: The comparison of the images contrast of Jaszczak phantom spheres indicated that generally with increasing the hole diameter of collimator, the images contrast of the spheres were decreased. In order to, in comparison to the 1st energy window (60–160 keV), the 2nd energy window (60-400 keV) was increased the image contrast. The results showed that for a fixed collimator and septa thickness values (3.2 cm and 1.14mm, respectively), the optimal value of the hole diameter was found 2.35 mm. Also from the stand point of the image contrast, the optimal energy window was found ranging from 60 to 400 keV. Conclusion: By use of the evaluation of the images contrast of Jaszczak phantom by SIMIND Monte Carlo simulation study, the best contrast is obtained when by use of the wide energy window ranging from 60 to 400 keV, which increased the imaging system sensitivity and decreased variance of the activity estimation. Moreover, a ME collimator with fixed values of 3.2 cm and 1.14 mm for the collimator and septa thicknesses, respectively and a hole diameter of 2.35 mm can improve the 90Y activity estimation and provide a suitable image quality for the 90Y bremsstrahlung SPECT imaging.

This study compared the SPECT (single-photon emission computed tomography) images before and after applying an attenuation correction by using the CT (computed tomography) image in a SPECT/CT scan and examined depending of the change in image quality on the CT dose. A flangeless Esser PET (positron emission tomography) Phantom was used to evaluate the image quality for the Precedence 16 SPECT/CT system manufactured by Philips. The experimental method was to obtain a SPECT image and a CT image of a flangeless Esser PET Phantom to acquire an attenuation-corrected SPECT image. A ROI (region of interest) was then set up at a hot spot of the acquired image to measure the SNR (signal to noise ratio) and the FWHM (full width at half maximum) and to compare the image quality with that of an unattenuation-corrected SPECT image. To evaluate the quality of a SPECT image, we set the ROI as a cylinder diameter (25, 16, 12, and 8 mm) and the BKG (background) radioactivity of the phantom images was obtained when each CT condition was changed. Subsequently, the counts were compared to measure the SNR. The FWHM of the smallest cylinder (8 mm) was measured to compare the image quality. A comparison of the SPECT images with and without attenuation correction revealed 5.01-fold, 4.77 fold, 4.43-fold, 4.38-fold, and 5.13-fold differences in SNR for the 25-mm cylinder, 16-mm cylinder, 12-mm cylinder, 8-mm cylinder, and BKG, respectively. In the phantom image obtained when the CT dose was changed, the FWHM of the 8-mm cylinder showed almost no difference under each condition regardless of the changes in kVp and mAs.

Introduction: Acquiring a high quality image has assigned an important concern for obtaining accurate diagnosis in nuclear medicine. Detector and collimator are critical component of Single Photon Emission Computed Tomography (SPECT) imaging system for giving accurate information from exact pattern of radionuclide distribution in the target organ. The images are strongly affected by the attenuation, scattering, and response of the detector and collimator. Method and material: The Planar and SPECT scans of a Y90 point source and also an extended Cardiac- Torso(XCAT) computerized phantom with the experiment and simulated systems were prepared. The SIMIND Monte Carlo program was used for simulating Siemen’s dual head variable angle SPECT imaging system with 4 detectors and 10 collimators. After verification and validation of the simulated system, the similar scans of the phantoms were compared from the point of view of image quality for 4 scintillator crystals including: NaI(Tl), BGO, LuAG: Ce, LaBr3 and also 10 collimators: Pb, Pb-Sb, Pb-Sb3, Pb-bi-Sn19, Pb-bi Sn375, Pb-bi-Sn50, Pb-bi-Sn-cd10, Pb-bi-Sn-cd125, Pt and Pt-Co. The parameters of energy and spatial resolution, and sensitivity of the systems were compared. Images were analyzed qualitatively by two nuclear medicine specialists. RESULTS: FWHM of the mentioned crystals and collimators obtained where: NaI (Pb, 0.3853) and BGO (Pb-Sb, 0.406), (Pb-Bi-Sn375, 0.405), (Pb-Bi-Sn-cd125, 0.375), and LuAG: Ce crystal (Pb-Sb, 0.425), (Pb- Bi-Sn19, 0.407), (Pb-Bi-Sn375, 0.417) and also LaBr3 (Pb-Bi-Sn375, 0.407), (Pb-Bi-Sn50, 0.430), (Pt-Co, 0.355). Medical diagnosis of the SPECT images of the phantom showed that the system with NaI(Tl)and LaBr3 by Pb-Sn3 collimator potentially provides a better detectability for hot lesions in the liver of XCAT phantom. CONCLUSIONS: The results showed that crystal NaI(Tl)and LaBr3 by Pb-Sn3 collimator has a high sensitivity and resolution, and also provides a better lesion detectability from the point of view of image quality on XCAT phantom.

Purpose:In yttrium-90 (Y-90) single-photon emission computed tomography (SPECT) imaging, the choice of the acquisition energy window is not trivial, due to the continuous and broad energy distribution of the bremsstrahlung photons. In this work, we investigate the effects of the energy windows on the image contrast to noise ratio (CNR), in order to select the optimal energy window for Y-90 imaging.Materials and Methods:We used the Monte Carlo SIMIND code to simulate the Jaszczak phantom which consists of the six hot spheres filled with Y-90 and ranging from 9.5 to 31.8 mm in diameter. Siemens Symbia gamma camera fitted with a high-energy collimator was simulated. To evaluate the effect of the energy windows on the image contrast, five narrow and large energy windows were assessed.Results:The optimal energy window obtained for Y-90 bremsstrahlung SPECT imaging was 120–150 keV. Furthermore, the results obtained for CNR indicate that the high detection is only for the three large spheres.Conclusion:The optimization of energy window in Y-90 bremsstrahlung has the potential to improve the image quality.

Introduction:In lutetium-177 (Lu-177) single-photon emission computed tomography (SPECT) imaging, the accuracy of activity quantification is degraded by penetrated and scattered photons. We assessed the scattered photon fractions in order to determine the optimal situation and development of correction method. This study proposes to compare the image quality that can be achieved by three collimators.Materials and Methods:Siemens Medical System Symbia fitted with high-energy (HE), medium-energy (ME), and low-energy high-resolution collimators was simulated using the SIMIND Monte Carlo code simulation code. Counts were collected in three different main-energy window widths (20%, 15%, and 10%) for Lu-177 point source. Primary and scattered point spread functions and also geometric, penetration, scattering were drawn and analyzed.Results:In Lu-177 imaging, a 20% of main-energy window and ME collimator were found to be optimal. HE collimator can be used when the resolution is not required.Conclusion:These results provide the optimal energy window and collimator in Lu-177 SPECT imaging and will help the quantification of Lu-177.

Strontium-89 chloride ((89)Sr) bremsstrahlung single photon emission computed tomography (SPECT) imaging was evaluated for detecting more detailed whole body (89)Sr distribution. (89)Sr bremsstrahlung whole body planar and merged SPECT images were acquired using two-detector SPECT system. Energy window A (100 keV ± 50 %) for planar imaging and energy window A plus adjacent energy window B (300 keV ± 50 %) for SPECT imaging were set on the continuous spectrum. Thirteen patients with multiple bone metastases were evaluated. Bone metastases can be detected with (99m)Tc-HMDP whole body planar and merged SPECT images and compared with (89)Sr bremsstrahlung whole body planar and merged SPECT images. Based on the location of metastatic lesions seen as hot spots on (99m)Tc-HMDP images as a reference, the hot spots on (89)Sr bremsstrahlung images were divided into the same bone parts as (99m)Tc-HMDP images (a total of 35 parts in the whole body), and the number of hot spots were counted. We also evaluated the incidence of extra-osseous uptakes in the intestine on (89)Sr bremsstrahlung whole body planar images. A total of 195 bone metastatic lesions were detected in both (99m)Tc-HMDP whole body planar and merged SPECT images. Detection of hot spot lesions in (89)Sr merged SPECT images (127 of 195; 66 %) was more frequent than in (89)Sr whole body planar images (108 of 195; 56 %), based on metastatic bone lesions in (99m)Tc-HMDP whole body planar and merged SPECT images. A large intestinal (89)Sr accumulation was detected in 5 of the 13 patients (38 %). (89)Sr bremsstrahlung-merged SPECT imaging could be more useful for detailed detection of whole body (89)Sr distribution than planar imaging. Intestinal (89)Sr accumulation due to (89)Sr physiologic excretion was detected in feces for 4 days after tracer injection.

In yttrium-90 ((90)Y) microsphere brachytherapy (radioembolization) of unresectable liver cancer, posttherapy (90)Y bremsstrahlung single photon emission computed tomography (SPECT) has been used to document the distribution of microspheres in the patient and to help predict potential side effects. The energy window used during projection acquisition can have a significant effect on image quality. Thus, using an optimal energy window is desirable. However, there has been great variability in the choice of energy window due to the continuous and broad energy distribution of (90)Y bremsstrahlung photons. The area under the receiver operating characteristic curve (AUC) for the ideal observer (IO) is a widely used figure of merit (FOM) for optimizing the imaging system for detection tasks. The IO implicitly assumes a perfect model of the image formation process. However, for (90)Y bremsstrahlung SPECT there can be substantial model-mismatch (i.e., difference between the actual image formation process and the model of it assumed in reconstruction), and the amount of the model-mismatch depends on the energy window. It is thus important to account for the degradation of the observer performance due to model-mismatch in the optimization of the energy window. The purpose of this paper is to optimize the energy window for (90)Y bremsstrahlung SPECT for a detection task while taking into account the effects of the model-mismatch. An observer, termed the ideal observer with model-mismatch (IO-MM), has been proposed previously to account for the effects of the model-mismatch on IO performance. In this work, the AUC for the IO-MM was used as the FOM for the optimization. To provide a clinically realistic object model and imaging simulation, the authors used a background-known-statistically and signal-known-statistically task. The background was modeled as multiple compartments in the liver with activity parameters independently following a Gaussian distribution; the signal was modeled as a tumor with a Gaussian-distributed activity parameter located randomly with equal probability at one of three positions. The IO test statistics (i.e., likelihood ratios) were estimated using Markov-chain Monte Carlo methods. The authors realistically modeled human anatomy using a digital phantom code, and realistically simulated (90)Y bremsstrahlung SPECT imaging with a clinical SPECT system and typical imaging parameters using a previously validated Monte Carlo bremsstrahlung simulation method. Model-mismatch was included by modeling image formation process in the calculation of IO test statistics using an analytic modeling method previously developed for quantitative (90)Y bremsstrahlung SPECT. To demonstrate the effects of the model-mismatch on the detection task, the authors optimized the energy window both with and without model-mismatch included in the IO. For all the energy windows, the AUC values for the IO-MM were smaller than that for the IO. The optimal windows for the IO-MM and the IO were 80-180 and 60-400 keV, respectively. The authors have demonstrated the degradation of the ideal performance due to model-mismatch and optimized the energy window for (90)Y bremsstrahlung SPECT for detection tasks by accounting for the effects of the model-mismatch. The obtained optimal window was much narrower when taking into account the model-mismatch and similar to that obtained previously for estimation tasks.

(Introduction) Major problems of single photon emission computed tomography (SPECT) which degrade images both qualitatively and quantitatively include attenuation, camera uniformity geometric collimator response, and scattered photons. Compton scattered photons degrade spatial resolution and reduce the accuracy and precison of quantiation in SPECT images. The majority of correction methods introduced to reduce influence of compton scatter component consider the scatter distribution function to be a symmetrical, monoexponential function of distance from source position. Here a more realistic approach has been taken to derive scatter distribution functions for usiform and nonuniform scattering geometries. (Method) Monte Carlo simulations of Tc-99m point and line sources were used to obtain detailed information on the spatial and energy distribution of scattered and non-scattered events in SPECT images. EGS4 simulation code was adapted for use with planar and SPECT imaging geometries and detection devices. Simulations were carried out in two steps : 1) photons were followed in attenuation media until they were completely absorbed or emerged. Photon energy, input and output coordinates, direction and scatter order were recorded for photons that emerged within the detector field of view. 2) The detection process was simulated in a second step which gave greater flexibility in changing detection parameters (collimator geometry, intrinsic spatial resolution, energy resolution, energy window settings etc.). Scatter in the collimator and septal penetration were not included. Energy resolution of the system was simulated by sampling from an energydependent Gaussian function. The data shown were obtained from a simulation of SPECT system with a LEHR collimator, radius of rotation of 13cm, an energy resolution of 13%, intrinsic spatial resolution of 3.6mm, an energy window of 20% centered at 140KeV and a pixel size of 1mm. Seperate images were obtained for nonscattered events and events of scatter order n=1-3, a single image was obtained for n>4. (Results) The scatter distribution function in non-uniform density media indicates that scatter correction techniqes based on single exponential scatter distribution function do not provide a valid correction for non-uniform scattering geometries. Further investigations of SDF in more complex non-uniform geometries are needed to develop accurate correction method for Compton scatter reduction in SPECT images. My results suggest that 3-D scatter correction function and reconstruction methods need to be applied.

Quantitative Yttrium-90 (90Y) bremsstrahlung single photon emission computed tomography (SPECT) imaging has shown great potential to provide reliable estimates of 90Y activity distribution for targeted radionuclide therapy dosimetry applications. One factor that potentially affects the reliability of the activity estimates is the choice of the acquisition energy window. In contrast to imaging conventional gamma photon emitters where the acquisition energy windows are usually placed around photopeaks, there has been great variation in the choice of the acquisition energy window for 90Y imaging due to the continuous and broad energy distribution of the bremsstrahlung photons. In quantitative imaging of conventional gamma photon emitters, previous methods for optimizing the acquisition energy window assumed unbiased estimators and used the variance in the estimates as a figure of merit (FOM). However, for situations, such as 90Y imaging, where there are errors in the modeling of the image formation process used in the reconstruction there will be bias in the activity estimates. In 90Y bremsstrahlung imaging this will be especially important due to the high levels of scatter, multiple scatter, and collimator septal penetration and scatter. Thus variance will not be a complete measure of reliability of the estimates and thus is not a complete FOM. To address this, we first aimed to develop a new method to optimize the energy window that accounts for both the bias due to model-mismatch and the variance of the activity estimates. We applied this method to optimize the acquisition energy window for quantitative 90Y bremsstrahlung SPECT imaging in microsphere brachytherapy. Since absorbed dose is defined as the absorbed energy from the radiation per unit mass of tissues in this new method we proposed a mass-weighted root mean squared error of the volume of interest (VOI) activity estimates as the FOM. To calculate this FOM, two analytical expressions were derived for calculating the bias due to model-mismatch and the variance of the VOI activity estimates, respectively. To obtain the optimal acquisition energy window for general situations of interest in clinical 90Y microsphere imaging, we generated phantoms with multiple tumors of various sizes and various tumor-to-normal activity concentration ratios using a digital phantom that realistically simulates human anatomy, simulated 90Y microsphere imaging with a clinical SPECT system and typical imaging parameters using a previously validated Monte Carlo simulation code, and used a previously proposed method for modeling the image degrading effects in quantitative SPECT reconstruction. The obtained optimal acquisition energy window was 100–160 keV. The values of the proposed FOM were much larger than the FOM taking into account only the variance of the activity estimates, thus demonstrating in our experiment that the bias of the activity estimates due to model-mismatch was a more important factor than the variance in terms of limiting the reliability of activity estimates.

Back to table of contents Previous article Next article Communications and UpdatesFull AccessBrain SPECT Imaging in Clinical PracticeDaniel Amen, M.D.Daniel AmenNewport Beach, Calif.Search for more papers by this author, M.D.Published Online:1 Sep 2010https://doi.org/10.1176/appi.ajp.2010.10060814AboutSectionsPDF/EPUB ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InEmail To the Editor: I agree with the statement by Bryon Adinoff, M.D., and Michael Devous, Ph.D. (1), in their Letter to the Editor published in the May 2010 issue of the Journal, that “it is likely that, within the next decade, Dr. Amen's claims [and fervent hope] will be realized in that psychiatrists will enjoy the ability to diagnose and prescribe treatments based, in part, upon neuroimaging findings” (1, p. 598). Imaging is now being used by psychiatrists here in the United States, in Canada, and abroad to aid patients. I cannot imagine anything more damaging to the imaging field, however, than encouraging medical board investigations for those who are early adopters. The California Medical Board investigated my use of single photon emission computed tomography (SPECT) 13 years ago, found no violation, and encouraged me to publish our findings, which I have done.One would think that a more enlightened attitude toward a field, as plagued by uncertainties as psychiatry still is, would welcome the practical application of neuroimaging. In 2001, Camargo wrote “Brain SPECT is rapidly becoming a clinical tool in many places, particularly in dementias, head injury, [obsessive compulsive disorder] OCD, Tourette's, schizophrenia, depression, panic disorder, and drug abuse” (2). Additionally, Brockman demonstrated SPECT's usefulness in choosing between treatments for depression (3).Our work is based on hundreds of texts and scientific articles, including 26 articles and the chapter on functional imaging in the Comprehensive Textbook of Psychiatry that I co-authored (4). Respected hospitals, such as Sierra Tucson, have added SPECT to their armamentarium. Thoughtful clinicians would never use SPECT in isolation, and contrary to what was written about me, I have never recommended such use.Clinical practice and careful observations have provided researchers with important hypotheses to test, and I have successfully invited researchers to use our database of rigorously diagnosed patients, including SPECT when indicated, to advance neuroimaging, and I extend the same invitation here.The Society of Nuclear Medicine has never formally approached me to perform a study. Plus, I would never engage in a charade where I was expected to give a diagnosis from a scan. That is not how imaging is or should be practiced. The notion of Adinoff and Devous that SPECT is dangerous is disingenuous. Devous recently wrote, “SPECT and PET have no more risk than MRI-based procedures” (5).The hope that SPECT and other imaging modalities will be as routine and useful to psychiatry as imaging the heart is to cardiology has animated my practice for nearly 20 years. It, indeed, is starting to happen. My hope is that our journal will help translate imaging research into clinical practice rather than threaten practitioners who have been trying to make it happen.Newport Beach, Calif.accepted for publication in June 2010.Dr. Amen is the CEO and owner of Amen Clinics, Inc.Reference1. Adinoff B , Devous MD: Scientifically unfounded claims in diagnosing and treating patients. Am J Psychiatry 2010; 167:598–598Link, Google Scholar2. Camargo EE: Brain SPECT in neurology and psychiatry. J Nucl Med 2001; 42:611–623Medline, Google Scholar3. Brockmann H , Zobel A , Joe A , Biermann K , Scheef L , Schuhmacher A , von Widdern O , Metten M , Biersack HJ , Maier W , Boecker H: The value of HMPAO SPECT in predicting treatment response to citalopram in patients with major depression. Psychiatry Res 2009; 173:107–112Crossref, Medline, Google Scholar4. http://www.amenclinics.com/meet-dr-amen/credentials/Google Scholar5. Devous MD: SPECT functional brain imaging, in Functional Cerebral SPECT and PET Imaging. Edited by Van Heertum RLTikofsky RSIchise M. Philadelphia, Lippincott, Williams and Wilkins, 2009Google Scholar FiguresReferencesCited byDetailsCited ByThe Potential for Medicolegal Abuse: Diffusion Tensor Imaging in Traumatic Brain Injury18 March 2014 | AJOB Neuroscience, Vol. 5, No. 2Triangulating perspectives on functional neuroimaging for disorders of mental health8 August 2013 | BMC Psychiatry, Vol. 13, No. 1AJOB Neuroscience, Vol. 3, No. 4Journal of Neurotrauma, Vol. 29, No. 14 Volume 167Issue 9 September 2010Pages 1125-1125 Metrics PDF download History Accepted 1 June 2010 Published online 1 September 2010 Published in print 1 September 2010

Dual-isotope (DI) studies offer a number of advantages in pre-clinical imaging. These include: reducing study times when compared with sequential scans, reducing the number of animals required for any given study, and most importantly, producing images perfectly registered in space and time that provide simultaneous information about two distinct body functions. The ability of single photon emission computed tomography (SPECT) to measure and differentiate energies of the emitted photons makes it well suited for DI imaging. However, since scattered photons originating from one radioisotope may be detected in the energy window of the other and thus degrade image quality and quantitative accuracy, scatter and crosstalk corrections must be applied.The decay characteristics of 111In and 67Ga, which are suitable for quantitative DI imaging for up to 2 weeks post-injection, led us to investigate the performance of simultaneous 111In/67Ga SPECT imaging using a small-animal pre-clinical scanner. A series of phantom experiments were performed to investigate image quality and accuracy of activity quantification in 111In/67Ga images acquired with three different collimators and reconstructed from different photopeak combinations. The triple energy window (TEW) method was used to correct for scatter and crosstalk. Based on these phantom studies, the optimal selection of collimator and energy window settings was determined. When using these optimal settings, submillimeter-size structures were distinguishable in the reconstructed images and quantification errors below 20% were achieved for both isotopes. The optimal parameters were subsequently applied to an in vivo animal study. The determination of the distinct pharmacokinetic profiles of two polymer radiopharmaceuticals injected simultaneously, but by different administration routes (intravenously and intraperitoneally) into a single animal demonstrated the feasibility of simultaneous 111In/67Ga SPECT.

To investigate the impact of x-ray beam energy, exposure intensity, and flat-bed scanner uniformity and spatial resolution on the precision of computed tomography (CT) beam width measurements using Gafchromic XR-QA2 film and an off-the-shelf document scanner. Small strips of Gafchromic film were placed at isocenter in a CT scanner and exposed at various x-ray beam energies (80-140 kVp), exposure levels (50-400 mA s), and nominal beam widths (1.25, 5, and 10 mm). The films were scanned in reflection mode on a Ricoh MP3501 flat-bed document scanner using several spatial resolution settings (100 to 400 dpi) and at different locations on the scanner bed. Reflection measurements were captured in digital image files and radiation dose profiles generated by converting the image pixel values to air kerma through film calibration. Beam widths were characterized by full width at half maximum (FWHM) and full width at tenth maximum (FWTM) of dose profiles. Dependences of these parameters on the above factors were quantified in percentage change from the baselines. The uncertainties in both FWHM and FWTM caused by varying beam energy, exposure level, and scanner uniformity were all within 4.5% and 7.6%, respectively. Increasing scanner spatial resolution significantly increased the uncertainty in both FWHM and FWTM, with FWTM affected by almost 8 times more than FWHM (48.7% vs 6.5%). When uncalibrated dose profiles were used, FWHM and FWTM were over-estimated by 11.6% and 7.6%, respectively. Narrower beam width appeared more sensitive to the film calibration than the wider ones (R(2) = 0.68 and 0.85 for FWHM and FWTM, respectively). The global and maximum local background variations of the document scanner were 1.2%. The intrinsic film nonuniformity for an unexposed film was 0.3%. Measurement of CT beam widths using Gafchromic XR-QA2 films is robust against x-ray energy, exposure level, and scanner uniformity. With proper film calibration and scanner resolution setting, it can provide adequate precision for meeting ACR and manufacturer's tolerances for the measurement of CT dose profiles.

To develop a practical background compensation (BC) technique to improve quantitative (90)Y-bremsstrahlung single-photon emission computed tomography (SPECT)/computed tomography (CT) using a commercially available imaging system. All images were acquired using medium-energy collimation in six energy windows (EWs), ranging from 70 to 410 keV. The EWs were determined based on the signal-to-background ratio in planar images of an acrylic phantom of different thicknesses (2-16 cm) positioned below a (90)Y source and set at different distances (15-35 cm) from a gamma camera. The authors adapted the widely used EW-based scatter-correction technique by modeling the BC as scaled images. The BC EW was determined empirically in SPECT/CT studies using an IEC phantom based on the sphere activity recovery and residual activity in the cold lung insert. The scaling factor was calculated from 20 clinical planar (90)Y images. Reconstruction parameters were optimized in the same SPECT images for improved image quantification and contrast. A count-to-activity calibration factor was calculated from 30 clinical (90)Y images. The authors found that the most appropriate imaging EW range was 90-125 keV. BC was modeled as 0.53× images in the EW of 310-410 keV. The background-compensated clinical images had higher image contrast than uncompensated images. The maximum deviation of their SPECT calibration in clinical studies was lowest (<10%) for SPECT with attenuation correction (AC) and SPECT with AC + BC. Using the proposed SPECT-with-AC + BC reconstruction protocol, the authors found that the recovery coefficient of a 37-mm sphere (in a 10-mm volume of interest) increased from 39% to 90% and that the residual activity in the lung insert decreased from 44% to 14% over that of SPECT images with AC alone. The proposed EW-based BC model was developed for (90)Y bremsstrahlung imaging. SPECT with AC + BC gave improved lesion detectability and activity quantification compared to SPECT with AC only. The proposed methodology can readily be used to tailor (90)Y SPECT/CT acquisition and reconstruction protocols with different SPECT/CT systems for quantification and improved image quality in clinical settings.