Quantitative SPECT Imaging Research Articles

MO‐B‐M100J‐01: Determination of Dose to Individual Patients in Radionuclide Imaging Procedures Including Planar, SPECT, and PET

Patient absorbed dose estimation due to internal emitters requires two separate computations prior to using the D = S*à formula. Here, D is the desired vector of target organ doses, S is a rectangular matrix of dose per radiodecay and à is a vector of cumulated activity curves for the various source organs in the patient. While S may be accessed from tabulations such as the OLINDA program from Vanderbilt University, à may be computed only by integrating activity curves A(t) out to sufficiently long times. Several methods are available to determine the activity in a given source organ. One may have tissues or lesions near the surface so as to use inverse square computations. At depth, the observer can use gamma cameras and a geometric mean image (GM), CT assisted matrix inversion (CAMI) or quantitative SPECT imaging. In the latter two cases, hybrid imaging devices such as SPECT/CT make the computations easier since image registration is greatly facilitated. There is also a possibility of PET/CT hybrid images being implemented with the SUV value being used to find the activity at‐depth. Lack of suitable positron labels makes PET studies problematic in the case of a general radiopharmaceutical, however. Errors in activity quantitation are typically on the order of +/− 30%, although they can be much larger in geometrically complicated cases. Two types of S values are commonly used. In type I computations, S refers to a phantom of appropriate size; e.g., adult male or female. Such dose estimates are included in applications to regulatory agencies (e.g. FDA). Additionally, type I results may be used to compare similar radiopharmaceuticals with regard to absorbed dose levels. Both diagnostic and therapeutic radiopharmaceuticals may be of interest. Type II calculations usually refer to a specific patient undergoing internal emitter therapy. Generally, alpha or beta emitters are used in this context. One may use Monte Carlo (MC) methods to find the S or correct tabulated phantom S elements to those approximating the patient. Since therapy involves short‐range emitters, S becomes diagonal and the correction is done via; S(patient) = S(phantom)*organ mass (phantom)/organ mass (patient). Such corrections can be very large — on the order of factors of two‐ or three‐fold. Finally, the uncertainty in the dose values may be estimated by combining errors in both S and Ã.Educational Objectives:1. Understand the matrix equation D = S*à for estimating internal emitter radiation doses to target organs.4. Know the various methods to estimate source organ activity.5. Realize that there are two types of calculations for dose; standard phantom or patient‐specific.6. Know how to estimate uncertainties in the dose calculation.

｀９９ｍ´Ｔｃ‐ＥＣＤを用いた，脳循環予備能評価法（ＴＩＥ法）の自動定量解析ツールの開発と臨床例での検証

In nuclear medicine, cerebral vascular reserve(CVR) is evaluated using technetium-99m ethyl cysteinate dimer [99mTc-ECD] and acetazolamide(ACZ). We developed a protocol involving the intravenous injection of 99mTc-ECD in three divided doses(TIE method), and have found that the cerebrovascular response to ACZ depended on time after ACZ administration. However, it was difficult to obtain high-precision quantitative SPECT images by the conventional method because of complicated image processing and image degradation accompanying image subtraction. We recently developed software known as the Automatic Quantitative CVR Estimation Tool(hereinafter referred to as Triple AQCEL), which, after the input of simple parameters, enables us to carry out automatic reconstruction of quantitative SPECT images without image degradation due to subtraction. Triple AQCEL was determined to reduce image degradation caused by subtraction and to provide valid quantitative data. Because Triple AQCEL does not require manual determination of ROI or image selection for the reconstruction of quantitative SPECT images, reproducibility of regional cerebral blood flow by 3DSRT is ensured. Since all analyses in evaluation by the TIE method are automated and the operator plays no part in them, with the resulting increase of throughput, this software will contribute to improved reproducibility of regional cerebral blood flow data, and will be useful in clinical pathophysiological assessment both preoperatively and during postoperative follow-up.

Comparison of conventional, model-based quantitative planar, and quantitative SPECT image processing methods for organ activity estimation using In-111 agents

Accurate quantification of organ radionuclide uptake is important for patient-specific dosimetry. The quantitative accuracy from conventional conjugate view methods is limited by overlap of projections from different organs and background activity, and attenuation and scatter. In this work, we propose and validate a quantitative planar (QPlanar) processing method based on maximum likelihood (ML) estimation of organ activities using 3D organ VOIs and a projector that models the image degrading effects. Both a physical phantom experiment and Monte Carlo simulation (MCS) studies were used to evaluate the new method. In these studies, the accuracies and precisions of organ activity estimates for the QPlanar method were compared with those from conventional planar (CPlanar) processing methods with various corrections for scatter, attenuation and organ overlap, and a quantitative SPECT (QSPECT) processing method. Experimental planar and SPECT projections and registered CT data from an RSD Torso phantom were obtained using a GE Millenium VH/Hawkeye system. The MCS data were obtained from the 3D NCAT phantom with organ activity distributions that modelled the uptake of 111In ibritumomab tiuxetan. The simulations were performed using parameters appropriate for the same system used in the RSD torso phantom experiment. The organ activity estimates obtained from the CPlanar, QPlanar and QSPECT methods from both experiments were compared. From the results of the MCS experiment, even with ideal organ overlap correction and background subtraction, CPlanar methods provided limited quantitative accuracy. The QPlanar method with accurate modelling of the physical factors increased the quantitative accuracy at the cost of requiring estimates of the organ VOIs in 3D. The accuracy of QPlanar approached that of QSPECT, but required much less acquisition and computation time. Similar results were obtained from the physical phantom experiment. We conclude that the QPlanar method, based on 3D organ VOIs and accurate models of the projection process, provided a substantial increase in accuracy of organ activity estimates from planar images compared to CPlanar processing and had accuracy approaching that of QSPECT.

Model-based compensation for quantitative 123I brain SPECT imaging

Previously we have developed a model-based method that can accurately estimate downscatter contamination from high-energy photons in 123I imaging. In this work we combined the model-based method with iterative reconstruction-based compensations for other image-degrading factors such as attenuation, scatter, the collimator-detector response function (CDRF) and partial volume effects to form a comprehensive method for performing quantitative 123I SPECT image reconstruction. In the model-based downscatter estimation method, photon scatter inside the object was modelled using the effective source scatter estimation (ESSE) technique, including contributions from all the photon emissions. The CDRFs, including the penetration and scatter components due to the high-energy 123I photons, were estimated using Monte Carlo (MC) simulations of point sources in air at various distances from the face of the collimator. The downscatter contamination was then compensated for during the iterative reconstruction by adding the estimated results to the projection steps. The model-based downscatter compensation (MBDC) was evaluated using MC simulated and experimentally acquired projection data. From the MC simulation, we found about 39% of the total counts in the energy window of 123I were attributed to the downscatter contamination, which reduced image contrast and caused a 1.5% to 10% overestimation of activities in various brain structures. Model-based estimates of the downscatter contamination were in good agreement with the simulated data. Compensation using MBDC removed the contamination and improved the image contrast and quantitative accuracy to that of the images obtained from 159 keV photons. The errors in absolute quantitation were reduced to within ±3.5%. The striatal specific binding potential calculated based on the activity ratio to the background was also improved after MBDC. The errors were reduced from −4.5% to −10.93% without compensation to −0.55% to 4.87% after compensation. The model-based method provided accurate downscatter estimation and, when combined with iterative reconstruction-based compensations, accurate quantitation was obtained with minimal loss of precision.

2.慢性期脳主幹動脈閉塞症における定量的脳血流SPECT読影のピットフォール(LS-10 画像診断の進歩(血流,PET),ランチョンセミナー,第26回 日本脳神経外科コングレス総会)

2.慢性期脳主幹動脈閉塞症における定量的脳血流SPECT読影のピットフォール(LS-10 画像診断の進歩(血流,PET),ランチョンセミナー,第26回 日本脳神経外科コングレス総会)

A Monte Carlo and physical phantom evaluation of quantitative In-111 SPECT

Accurate estimation of the 3D in vivo activity distribution is important for dose estimation in targeted radionuclide therapy (TRT). Although SPECT can potentially provide such estimates, SPECT without compensation for image degrading factors is not quantitatively accurate. In this work, we evaluated quantitative SPECT (QSPECT) reconstruction methods that include compensation for various physical effects. Experimental projection data were obtained using a GE VH/Hawkeye system and an RSD torso phantom. Known activities of In-111 chloride were placed in the lungs, liver, heart, background and two spherical compartments with inner diameters of 22 mm and 34 mm. The 3D NCAT phantom with organ activities based on clinically derived In-111 ibritumomab tiuxetan data was used for the Monte Carlo (MC) simulation studies. Low-noise projection data were simulated using previously validated MC simulation methods. Fifty sets of noisy projections with realistic count levels were generated. Reconstructions were performed using the OS-EM algorithm with various combinations of attenuation (A), scatter (S), geometric response (G), collimator–detector response (D) and partial volume compensation (PVC). The QSPECT images from the various combinations of compensations were evaluated in terms of the accuracy and precision of the estimates of the total activity in each organ. For experimental data, the errors in organ activities for ADS and PVC compensation were less than 6.5% except the smaller sphere (−11.9%). For the noisy simulated data, the errors in organ activity for ADS compensation were less than 5.5% except the lungs (20.9%) and blood vessels (15.2%). Errors for other combinations of compensations were significantly (A, AS) or somewhat (AGS) larger. With added PVC, the error in the organ activities improved slightly except for the lungs (11.5%) and blood vessels (3.6%) where the improvement was more substantial. The standard deviation/mean ratios were all less than 1.5%. We conclude that QSPECT methods with appropriate compensations provided accurate In-111 organ activity estimates. For the collimator used, AGS was almost as good as ADS and may be preferable due to the reduced reconstruction time. PVC was important for small structures such as tumours or for organs in close proximity to regions with high activity. The improved quantitative accuracy from QSPECT methods has the potential for improving organ dose estimations in TRT.

Partial volume effect compensation for quantitative brain SPECT imaging

Partial volume (PV) effects degrade the quantitative accuracy of SPECT brain images. In this paper, we extended a PV compensation (PVC) method originally developed for brain PET, the geometric transfer matrix (GTM) method, to brain SPECT using iterative reconstruction-based compensations. In the GTM method a linear transform between the true regional activities and the measured results was assumed. Elements of the GTM were calculated by projecting and reconstructing maps with uniform regions representing different structures. However, with iterative reconstruction methods, especially when reconstruction-based compensation for detector response was applied, we found that it was important to treat the region maps as a perturbation to the reconstructed image in the estimation of the GTM. This modified method, termed perturbation-based GTM (pGTM) was evaluated using Monte Carlo (MC) simulated and experimentally acquired data. Results showed great improvement of the quantitative accuracy in brain SPECT imaging. For MC simulated data, PVC using pGTM reduced the underestimation of striatal activities from 30% to less than 1.2%. For experimental data, PVC using pGTM reduced the underestimation of striatal activities from 36% to less than 7.8%. The underestimation of the striatum to background activity ratio was also improved from 31% to 2.7%.

Attenuation correction using combination of a parallel hole collimator and an uncollimated non-uniform line array source.

Attenuation correction is very important for quantitative SPECT imaging. We designed an uncollimated non-uniform line array source (non-uniform LAS) for attenuation correction based on transmission computed tomography (TCT) using Tc-99m and compared its performance with an uncollimated uniform line array source (uniform LAS) in a thorax phantom study. This non-uniform LAS was attached to one camera head of a dual-head gamma camera, and transmission data were acquired with another camera head with a low-energy, general purpose, parallel-hole collimator at 50 cm-distance apart from the source. The modified TEW using a subtraction factor of 1.0 was employed to correct scattered Tc-99m photons for transmission data. In the phantom experiment, eight TCT data were acquired with the scanning time changed from 2 minutes to 20 minutes for each LAS. The Tc-99m attenuation coefficient (mu) maps with the non-uniform LAS and uniform LAS improved the statistical count variation in the mediastinum filled with water as the scanning time got longer. The Tc-99m mu-map with the non-uniform LAS and 6 minutes of scanning time had equal quality at the center of the thorax phantom to that with the uniform LAS and 16 minutes of scanning time. In conclusion, for the TCT imaging with combination of the parallel hole collimator and uncollimated Tc-99m external source the non-uniform LAS can reduce the Tc-99m radioactivity or the TCT scanning time compared with the uniform LAS.

Improved quantitative GA-65 spect imaging

Improved quantitative GA-65 spect imaging

脳血行再建術における血行力学的脳虚血の定量的重症度評価

Hemodynamic cerebral ischemia can be stratified into Stage I and Stage II (Misery perfusion). According to vasodilatory and metabolic compensation toward reduction of CPP, Stage I ischemia is defined as both preservation of resting CBF and reduction of vascular reserve. Stage II ischemia is defined as reduction of resting CBF, loss of vascular reserve and elevation of oxygen extraction fraction (OEF). The vasodilatory response to acetazolamide, a carbonic anhydrase inhibitor, provides an effective parameter of cerebrovascular reserve. Recently, quantitative measurement of CBF and cerebrovascular reserve (VR): (acetazolamide-activated CBF / resting CBF — 1)× 100% was introduced in clinical practice and hemodynamic cerebral ischemia can be quantitatively stratified into Stage I and Stage II. Both 123I-IMP-microsphere method and 123I-IMP-ARG method indicate acceptable accuracy, and can be commonly used as quantitative brain perfusion SPECT imaging. In 123I-IMP-ARG methods, Stage I ischemia is defined as follows: resting CBF more than 34 ml/100 g/min (this value corresponds to 80% of mean CBF of normal subjects) or VR from 10% to 30%, Stage II ischemia is defined as follows: rCBF less than 34 ml/100 g/min and VR less than 10%. Hemodynamically normal subjects are involved in VR more than 30% (Stage 0).Twenty-four patients with hemodynamic stroke were selected for a recent EC-IC bypass study. In this study, EC-IC Bypass surgery was performed in patients with Stage II and I (nearly II) ischemia using 123I-IMP-ARG methods. In the affected areas, the mean values of resting CBF and VR after surgery (35.0+/−7.2 ml/100 g/min, 32.9+/−15.2%) were significantly improved compared with the values before surgery (29.6+/−5.3 ml, −4.5+/−12.4%). In the unaffected areas, the mean values of resting CBF and VR after surgery (38.8+/−7.9 ml/100 g/min, 40.8+/−15.8%) were not significantly different than those values before surgery. The stage after surgery (Stage 0 in 16, Stage I in 8, Stage II in 0) was statistically improved in comparison with the stage before surgery (Stage 0 in 0, Stage I in 7, Stage II in 17). Stage II hemodynamic cerebral ischemia defined by quantitative brain perfusion SPECT imaging was successfully reversed to Stage I or 0 by EC-IC Bypass surgery. A Japanese EC-IC Bypass trial (JET Study) is being carried out to clarify the surgical benefits for Stage II ischemia, and quantitative measurement of CBF and VR has been recognized to be essential for the inclusion criteria for this trial.99mTc-HMPAO or 99mTc-ECD-Patlak plot method could be another option for quantitative brain perfusion SPECT imaging. However, these methods can indicate acceptable values of resting CBF but could not demonstrate accurate values of VR activated by acetazolamide challenge. First-pass extraction of these radiotracers is generally lower in the relative high-flow range. Therefore the quantitative CBF value tends to be underestimated in the area with normally vasodilatory response under acetazolamide-activated condition. Linearization corrections should be modified in these methods, especially using acetazolamide activation.Hemodynamic cerebral ischemia can be stratified into Stage I and Stage II (Misery perfusion) and the stratification may be important to determine future risk of stroke. The characteristics and kinetics of brain perfusion radiotracers should be considered in quantitative stratification of hemodynamic cerebral ischemia using brain perfusion SPECT.

1.18 Comparative accuracy of iterative reconstruction algorithms in quantitative thallium-201 SPECT imaging

1.18 Comparative accuracy of iterative reconstruction algorithms in quantitative thallium-201 SPECT imaging

Project title improved quantitative GA-65 spect imaging

Project title improved quantitative GA-65 spect imaging

Quantitative Tc-99m Tetrofosmin SPECT Imaging in the Assessment of Coronary Artery Disease

Quantitative Tc-99m Tetrofosmin SPECT Imaging in the Assessment of Coronary Artery Disease

Prognostic Value of Quantitative Stress Myocardial SPECT Imaging in Patients With Unstable Angina

Prognostic Value of Quantitative Stress Myocardial SPECT Imaging in Patients With Unstable Angina

Prognostic value of quantitative stress myocardial SPECT imaging in patients with unstable angina

Prognostic value of quantitative stress myocardial SPECT imaging in patients with unstable angina

2.定量的な臨床SPECT画像を得るための注意点(SPECT装置の進歩と技術的問題点)

2.定量的な臨床SPECT画像を得るための注意点(SPECT装置の進歩と技術的問題点)

Quantitative Tc-99m tetrofosmin SPECT imaging in the assessment of coronary artery disease

Quantitative Tc-99m tetrofosmin SPECT imaging in the assessment of coronary artery disease

Usefulness of quantitative rest BMIPP SPECT imaging for detection of myocardial ischemia by using polar maps and standard normal limits

Usefulness of quantitative rest BMIPP SPECT imaging for detection of myocardial ischemia by using polar maps and standard normal limits

The relative importance of energy resolution for quantitative /sup 99m/Tc SPECT imaging

The authors seek to determine the desired energy resolution for quantitative SPECT imaging. As the energy resolution of the system is improved, the relative error due to scatter decreases. Yet, at some point the improvement becomes inconsequential since the scatter error is small compared to the other physical perturbations in the radionuclide measurement. In order to estimate the energy resolution at which this condition becomes true, the authors used a Monte Carlo code to simulate the emission data from a myocardial perfusion phantom. The data were reconstructed using a maximum likelihood code, and the images were analyzed to determine the relative effects of attenuation correction, collimator response compensation, noise, and scatter rejection on image quantitation. The simulations showed that improving the system energy resolution beyond 5 keV offers little benefit for myocardial perfusion studies as judged by the noise in a 9-pixel ROI. The relevance of this result to other applications is also discussed.

Measured accuracy and precision in quantitative SPECT imaging with iodine-123

This study evaluated /sup 123/I SPECT volume and activity quantitation in terms of accuracy and precision using experimental phantom data. Two reconstruction methods were considered. The filtered backprojection (FB) method with 2D Metz pre-filtering and single iteration Chang attenuation compensation was compared with an iterative ML-EM method that used Gaussian post-filtering and incorporated the 3D divergent detector response and attenuation in the detection kernel. Both methods were examined over a range of resolution and noise characteristics. An ensemble of 21 SPECT data sets were acquired of a cylindrical phantom that contained spheres of size 21.4, 12.0, and 5.7 ml, filled with high purity /sup 123/I in a uniform background (5:1 uptake ratio). Each data set was reconstructed by both methods, and sphere volume and activity measurements were obtained from the reconstructions using a semi-automatic method that defines the region-of-interest based on the intensity gradient in the area of increased /sup 123/I concentration. The mean and standard deviation of the 21 measurements provided accuracy and precision indices, respectively. For the 12.0 ml sphere, the measured volume with either reconstruction method was accurate to within 5% of the true volume with a standard deviation of approximately 8% of the true volume. For the 12.0 ml sphere the measured volume with the iterative method exhibited substantially smaller standard deviation for equal accuracy compared with the FB method. Sphere activity was underestimated with both methods due to spatial resolution effects. The 5.7 ml sphere was generally below the size limit for volume and activity quantitation by these methods. >