Absolute quantitative total-body small-animal SPECT with focusing pinholes

Wu, Chao; Have, Frans van der; Vastenhouw, Brendan; Dierckx, Rudi; Paans, Anne M. J.; Beekman, Freek J.

doi:10.1007/s00259-010-1519-9

Cited by 44 publications

(55 citation statements)

References 32 publications

(29 reference statements)

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“…Uptake of tracer in each compartment was determined by drawing a cylinder around the compartments with a diameter of 10 mm, larger than the cylinders themselves, to avoid partial-volume effects. SPECT and PET images were scaled to the same relative intensities using calibration factors for 99m Tc and 18 F that were determined by scanning a small source filled with a known quantity of 99m Tc or 18 F and then applying attenuation correction (27).…”

Section: Evaluation Of System Characteristicsmentioning

confidence: 99%

VECTor: A Preclinical Imaging System for Simultaneous Submillimeter SPECT and PET

et al. 2012

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Today, PET and SPECT tracers cannot be imaged simultaneously at high resolutions but require 2 separate imaging systems. This paper introduces a Versatile Emission Computed Tomography system (VECTor) for radionuclides that enables simultaneous submillimeter imaging of single-photon and positron-emitting radiolabeled molecules. Methods: g-photons produced both by electron-positron annihilation and by single-photon emitters are projected onto the same detectors by means of a novel cylindric high-energy collimator containing 162 narrow pinholes that are grouped in clusters. This collimator is placed in an existing SPECT system (U-SPECT-II) with 3 large-field-of-view g-detectors. From the acquired projections, PET and SPECT images are obtained using statistical image reconstruction that corrects for energy-dependent system blurring. Results: For PET tracers, the tomographic resolution obtained with a Jaszczak hot rod phantom was less than 0.8 mm, and 0.5-mm resolution images of SPECT tracers were acquired simultaneously. SPECT images were barely degraded by the simultaneous presence of a PET tracer, even when the activity concentration of the PET tracer exceeded that of the SPECT tracer by up to a factor of 2.5. Furthermore, we simultaneously acquired fully registered 3-and 4-dimensional multiple functional images from living mice that, in the past, could be obtained only sequentially. Conclusion: High-resolution complementary information about tissue function contained in SPECT and PET tracer distributions can now be obtained simultaneously using a fully integrated imaging device. These combined unique capabilities pave the way for new perspectives in imaging the biologic systems of rodents.

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Section: Evaluation Of System Characteristicsmentioning

confidence: 99%

VECTor: A Preclinical Imaging System for Simultaneous Submillimeter SPECT and PET

et al. 2012

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“…Absolute quantification in SPECT imaging is challenging and requires correction for effects such as collimator efficiency, attenuation, and scatter [32], [33]. In order to isolate the effects of the uniform and prior-image initial guesses on the reconstruction, we considered metrics that depend on the relative reconstructed activity rather than the absolute activity.…”

Section: Methodsmentioning

confidence: 99%

The Performance of MLEM for Dynamic Imaging From Simulated Few-View, Multi-Pinhole SPECT

Wolf

Clough

et al. 2013

IEEE Trans. Nucl. Sci.

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Stationary small-animal SPECT systems are being developed for rapid dynamic imaging from limited angular views. This paper quantified, through simulations, the performance of Maximum Likelihood Expectation Maximization (MLEM) for reconstructing a time-activity curve (TAC) with uptake duration of a few seconds from a stationary, three-camera multi-pinhole SPECT system. The study also quantified the benefits of a heuristic method of initializing the reconstruction with a prior image reconstructed from a conventional number of views, for example from data acquired during the late-study portion of the dynamic TAC. We refer to MLEM reconstruction initialized by a prior-image initial guess (IG) as MLEMig. The effect of the prior-image initial guess on the depiction of contrast between two regions of a static phantom was quantified over a range of angular sampling schemes. A TAC was modeled from the experimentally measured uptake of 99mTc-hexamethylpropyleneamine oxime (HMPAO) in the rat lung. The resulting time series of simulated images was quantitatively analyzed with respect to the accuracy of the estimated exponential washin and washout parameters. In both static and dynamic phantom studies, the prior-image initial guess improved the spatial depiction of the phantom, for example improved definition of the cylinder boundaries and more accurate quantification of relative contrast between cylinders. For example in the dynamic study, there was ~50% error in relative contrast for MLEM reconstructions compared to ~25-30% error for MLEMig. In the static phantom study, the benefits of the initial guess decreased as the number of views increased. The prior-image initial guess introduced an additive offset in the reconstructed dynamic images, likely due to biases introduced by the prior image. MLEM initialized with a uniform initial guess yielded images that faithfully reproduced the time dependence of the simulated TAC; there were no statistically significant differences in the mean exponential washin/washout parameters estimated from MLEM reconstructions compared to the true values. Washout parameters estimated from MLEMig reconstructions did not differ significantly from the true values, however the estimated washin parameter differed significantly from the true value in some cases. Overall, MLEM reconstruction from few views and a uniform initial guess accurately quantified the time dependance of the TAC while introducing errors in the spatial depiction of the object. Initializing the reconstruction with a late-study initial guess improved spatial accuracy while decreasing temporal accuracy in some cases.

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“…The contrast-to-noise ratio was defined as C d /N d . The quantification calibration procedure and determination of the calibration factors are described in the supplemental data and based on the method given in Wu et al (19).…”

Section: Phantom Experimentsmentioning

confidence: 99%

Utilizing High-Energy γ-Photons for High-Resolution ²¹³Bi SPECT in Mice

et al. 2015

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The combined α-, γ-, and x-ray emitter 213 Bi (half-life, 46 min) is promising for radionuclide therapy. SPECT imaging of 213 Bi is challenging, because most emitted photons have a much higher energy (440 keV) than common in SPECT. We assessed 213 Bi imaging capabilities of the Versatile Emission Computed Tomograph (VECTor) dedicated to (simultaneous) preclinical imaging of both SPECT and PET isotopes over a wide photon energy range of 25-600 keV. Methods: VECTor was equipped with a dedicated clustered pinhole collimator. Both the 79 keV x-rays and the 440 keV γ-rays emitted by 213 Bi could be imaged. Phantom experiments were performed to determine the maximum resolution, contrast-to-noise ratio, and activity recovery coefficient for different energy window settings. Additionally, imaging of [ 213 Bi-DOTA,Tyr 3 ]octreotate and 213 Bi-diethylene triamine pentaacetic acid (DTPA) in mouse models was performed. Results: Using 440 keV γ-rays instead of 79 keV x-rays in image reconstruction strongly improved the resolution (0.75 mm) and contrast-to-noise characteristics. Results obtained with a single 440 keV energy window setting were close to those with a combined 79 keV/440 keV window. We found a reliable activity recovery coefficient down to 0.240 MBq/mL with 30-min imaging time. In a tumor-bearing mouse injected with 3 MBq of [ 213 Bi-DOTA,Tyr 3 ]octreotate, tumor uptake could be visualized with a 1-h postmortem scan. Imaging a nontumor mouse at 5-min frames after injection of 7.4 MBq of 213 Bi-DTPA showed renal uptake and urinary clearance, visualizing the renal excretion pathway from cortex to ureter. Quantification of the uptake data allowed kinetic modeling and estimation of the absorbed dose to the kidneys. Conclusion: It is feasible to image 213 Bi down to a 0.75-mm resolution using a SPECT system equipped with a dedicated collimator. Newoppor tunities for high linear energy transfer radionuclide therapy with the a-particle emitters 225 Ac and 213 Bi are increasingly being investigated (1-3). The research for peptide receptor radionuclide therapy with a-particles is mostly focused on labeling peptides with 213 Bi. Not only is the short half-life of 46 min for 213 Bi in good accordance with the rapid targeting to receptor-positive tumors and the rapid clearance of peptides, it also raises less concern for detrimental effects because of the absence of nonspecific uptake by daughters detached from its peptide or linker due to a-decay recoil (4). 213 Bi offers the best imaging opportunities through its 440 keV g-ray and is therefore important for biodistribution and dosimetry studies (5). All other g-rays and x-rays emitted by 213 Bi and its daughters are too low either in abundance or in energy to be suitable for imaging, possibly with the exception of the x-rays from 213 Bi at 77 and 79 keV if appropriate correction methods for down-scatter of the 440 keV g-rays are applied (Supplemental Table 1; supplemental materials are available at http://jnm.snmjournals.org (6)). Patient imaging of the uptake patte...

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Absolute quantitative total-body small-animal SPECT with focusing pinholes

Cited by 44 publications

References 32 publications

VECTor: A Preclinical Imaging System for Simultaneous Submillimeter SPECT and PET

VECTor: A Preclinical Imaging System for Simultaneous Submillimeter SPECT and PET

The Performance of MLEM for Dynamic Imaging From Simulated Few-View, Multi-Pinhole SPECT

Utilizing High-Energy γ-Photons for High-Resolution ²¹³Bi SPECT in Mice

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Absolute quantitative total-body small-animal SPECT with focusing pinholes

Cited by 44 publications

References 32 publications

VECTor: A Preclinical Imaging System for Simultaneous Submillimeter SPECT and PET

VECTor: A Preclinical Imaging System for Simultaneous Submillimeter SPECT and PET

The Performance of MLEM for Dynamic Imaging From Simulated Few-View, Multi-Pinhole SPECT

Utilizing High-Energy γ-Photons for High-Resolution 213Bi SPECT in Mice

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Utilizing High-Energy γ-Photons for High-Resolution ²¹³Bi SPECT in Mice