Experimental determination of the weighting factor for the energy window subtraction-based downscatter correction for I-123 in brain SPECT studies

Nijs, Robin de; Holm, Sven; Thomsen, Gerda; Ziebell, Morten; Svarer, Claus

doi:10.4103/0971-6203.71765

Cited by 13 publications

(12 citation statements)

References 17 publications

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“…This point was addressed by investigating the relevance of extra-brain activity which is not accounted for in a phantom study. The high uptake and retention of [ 123 I]FP-CIT in lungs, liver, and intestines and sometimes in salivary glands and thyroid [ 9 ] is, in fact, expected to contribute to the brain image, particularly through septal penetration from the 123 I high-energy gamma emissions [ 10 , 11 ]. The magnitude of this contribution was indirectly estimated from a comparison of the phantom (brain activity only) and the human (brain and extra-brain activity) data for each camera.…”

Section: Methodsmentioning

confidence: 99%

[123I]FP-CIT ENC-DAT normal database: the impact of the reconstruction and quantification methods

et al. 2017

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Background[123I]FP-CIT is a well-established radiotracer for the diagnosis of dopaminergic degenerative disorders. The European Normal Control Database of DaTSCAN (ENC-DAT) of healthy controls has provided age and gender-specific reference values for the [123I]FP-CIT specific binding ratio (SBR) under optimised protocols for image acquisition and processing. Simpler reconstruction methods, however, are in use in many hospitals, often without implementation of attenuation and scatter corrections. This study investigates the impact on the reference values of simpler approaches using two quantifications methods, BRASS and Southampton, and explores the performance of the striatal phantom calibration in their harmonisation.ResultsBRASS and Southampton databases comprising 123 ENC-DAT subjects, from gamma cameras with parallel collimators, were reconstructed using filtered back projection (FBP) and iterative reconstruction OSEM without corrections (IRNC) and compared against the recommended OSEM with corrections for attenuation and scatter and septal penetration (ACSC), before and after applying phantom calibration. Differences between databases were quantified using the percentage difference of their SBR in the dopamine transporter-rich striatum, with their significance determined by the paired t test with Bonferroni correction.Attenuation and scatter losses, measured from the percentage difference between IRNC and ACSC databases, were of the order of 47% for both BRASS and Southampton quantifications. Phantom corrections were able to recover most of these losses, but the SBRs remained significantly lower than the “true” values (p < 0.001). Calibration provided, in fact, “first order” camera-dependent corrections, but could not include “second order” subject-dependent effects, such as septal penetration from extra-cranial activity. As for the ACSC databases, phantom calibration was instrumental in compensating for partial volume losses in BRASS (~67%, p < 0.001), while for the Southampton method, inherently free from them, it brought no significant changes and solely corrected for residual inter-camera variability (−0.2%, p = 0.44).ConclusionsThe ENC-DAT reference values are significantly dependent on the reconstruction and quantification methods and phantom calibration, while reducing the major part of their differences, is unable to fully harmonize them. Clinical use of any normal database, therefore, requires consistency with the processing methodology. Caution must be exercised when comparing data from different centres, recognising that the SBR may represent an “index” rather than a “true” value.

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Section: Methodsmentioning

confidence: 99%

[123I]FP-CIT ENC-DAT normal database: the impact of the reconstruction and quantification methods

et al. 2017

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“…In both detectors, the DEW method is limited by the inability to account for spatial distribution of scattered photons (see above). Moreover, it relies on calibration of the k factor which is then applied indiscriminately to the acquired dataset, and DEW cannot account for downscatter from the 529 keV iodine-123 peak (28,29); both adaptations would require a third energy window above the photopeak window. In CZT detectors, overestimation of scatter using the DEW method will result from the detector-speci c low-energy tail which is caused by contamination from photons that are unscattered but detected with lower energy (28,30).…”

Section: Discussionmentioning

confidence: 99%

Feasibility of iodine-123-mIBG SPECT/CT quantification in neuroblastoma using CZT and NaI detectors

Rogasch¹,

Bluemel²,

Großer³

et al. 2020

Preprint

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Background In [ 123 I]mIBG SPECT/CT for neuroblastoma, lesion uptake quantification could improve therapy monitoring. This study compared quantitative accuracy of a CZT (WEHR45) and NaI (LEHR) system (GE Discovery 670). Methods Volume sensitivity VS hom was estimated from a homogenous cylindrical phantom (811 ml) acquired with body contour or fixed 27 cm detector radius. Relative accuracy of VS hom to retrieve true background activity concentration (AC) in an IEC body phantom was calculated. Maximum/peak contrast recovery (CR) of the sphere inserts used VS IEC estimated from the IEC phantom. In 16 children with 37 [ 123 I]mIBG SPECT/CTs (range, 1-6 per patient; CZT, 12; NaI, 25), normal organ SUVmean (liver r/l, spleen, myocardium, blood pool, spine, muscles) were calculated using VS hom and VS IEC . Iterative reconstruction (Q.Metrix) used resolution recovery with/without scatter correction (SC) by dual energy window (DEW; 159 ± 10% and 130 ± 10% keV). In 20 exams, metabolic tumor volume (MTV)*SUVmax changes of primary tumors were correlated with changes of MRI tumor volume in serial scans (Pearson). Results VS hom (cts * MBq -1 * s -1 ) using SC was slightly lower for 27 cm radius vs. body contour with CZT (48 vs. 50, p<0.001) but comparable with NaI (59 vs. 61, p=0.18). Relative error in IEC phantom AC based on VS hom for CZT vs. NaI was -1.3% vs. +4.1% with SC (p=0.22). Acquisition time reduction by 50% (CZT) showed similar VS hom and relative error. CRmax/peak overestimated true AC in largest spheres (diameter, 22-37 mm) with SC and underestimated it without SC. Average SUVmean in liver and myocardium of CZT vs. NaI patients were similar. In the remaining organs (high estimated scatter proportions of >60% [CZT] or >40% [NaI]), average SUVmean differed between CZT and NaI, and coefficient of variation was significantly higher in SC vs. non-SC with CZT. MTV*SUVmax changes correlated with MRI volume changes with r=0.62 (non-SC) or r=0.59 (SC). Conclusions In principle, both CZT and NaI allow quantification in [ 123 I]mIBG SPECT/CT, but quantitative accuracy remains limited if using DEW for SC due to effects from source geometry (e.g. phantoms and organs) on scatter. Detector radius and acquisition time showed minor effects. MTV*SUVmax changes might be surrogate of response to therapy.

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“…The corrected image was calculated as follows 25:where the subscript ds is used to indicate the downscatter window.…”

Section: Methodsmentioning

confidence: 99%

Improving quantitative dosimetry in 177Lu-DOTATATE SPECT by energy window-based scatter corrections

Nijs

Lagerburg

Klausen

et al. 2014

Nuclear Medicine Communications

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PurposePatient-specific dosimetry of lutetium-177 (177Lu)-DOTATATE treatment in neuroendocrine tumours is important, because uptake differs across patients. Single photon emission computer tomography (SPECT)-based dosimetry requires a conversion factor between the obtained counts and the activity, which depends on the collimator type, the utilized energy windows and the applied scatter correction techniques. In this study, energy window subtraction-based scatter correction methods are compared experimentally and quantitatively.Materials and methods177Lu SPECT images of a phantom with known activity concentration ratio between the uniform background and filled hollow spheres were acquired for three different collimators: low-energy high resolution (LEHR), low-energy general purpose (LEGP) and medium-energy general purpose (MEGP). Counts were collected in several energy windows, and scatter correction was performed by applying different methods such as effective scatter source estimation (ESSE), triple-energy and dual-energy window, double-photopeak window and downscatter correction. The intensity ratio between the spheres and the background was measured and corrected for the partial volume effect and used to compare the performance of the methods.ResultsLow-energy collimators combined with 208 keV energy windows give rise to artefacts. For the 113 keV energy window, large differences were observed in the ratios for the spheres. For MEGP collimators with the ESSE correction technique, the measured ratio was close to the real ratio, and the differences between spheres were small.ConclusionFor quantitative 177Lu imaging MEGP collimators are advised. Both energy peaks can be utilized when the ESSE correction technique is applied. The difference between the calculated and the real ratio is less than 10% for both energy windows.

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Experimental determination of the weighting factor for the energy window subtraction-based downscatter correction for I-123 in brain SPECT studies

Cited by 13 publications

References 17 publications

[123I]FP-CIT ENC-DAT normal database: the impact of the reconstruction and quantification methods

[123I]FP-CIT ENC-DAT normal database: the impact of the reconstruction and quantification methods

Feasibility of iodine-123-mIBG SPECT/CT quantification in neuroblastoma using CZT and NaI detectors

Improving quantitative dosimetry in 177Lu-DOTATATE SPECT by energy window-based scatter corrections

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