# 360° CZT-SPECT/CT cameras: 99mTc- and 177Lu-phantom-based evaluation under clinical conditions

Christopher Hoog, Pierre-Malick Koulibaly, Nicolas Sas, Laetitia Imbert, Gilles Le Rouzic, Romain Popoff, Jean-Noël Badel, Ludovic Ferrer

► To cite this version:

Christopher Hoog, Pierre-Malick Koulibaly, Nicolas Sas, Laetitia Imbert, Gilles Le Rouzic, et al., 360° CZT-SPECT/CT cameras: 99mTc- and 177Lu-phantom-based evaluation under clinical conditions. EJNMMI Physics, 2024, 11 (1), pp.89. 10.1186/s40658-024-00684-6. hal-04887854

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# 360° CZT-SPECT/CT cameras: ⁹⁹mTc- and ¹⁷⁷Lu-phantom-based evaluation under clinical conditions

Christopher Hoog<fnref n="1" />* ID, Pierre-Malick Koulibaly<fnref n="2" />, Nicolas Sas<fnref n="3" />, Laetitia Imbert<fnref n="4" />, Gilles Le Rouzic<fnref n="5" />,
Romain Popoff<fnref n="6" />,<fnref n="7" />, Jean-Noël Badel<fnref n="8" /> and Ludovic Ferrer<fnref n="9" />,<fnref n="10" />

## Abstract

**Purpose:** For the first time, three currently available 360° CZT-SPECT/CT cameras were compared under clinical conditions using phantom-based measurements.

**Methods:** A ⁹⁹mTc- and a ¹⁷⁷Lu-customized NEMA IEC body phantom were imaged with three different cameras, StarGuide (GE Healthcare), VERITON-CT versions 200 (V200) and 400 (V400) (Spectrum Dynamics Medical) under the same clinical conditions. Energy resolution and volumetric sensitivity were evaluated from energy spectra. Vendors provided the best reconstruction parameters dedicated to visualization and/or quantification, based on their respective software developments. For both ⁹⁹mTc- and ¹⁷⁷Lu-phantoms, noise level, quantification accuracy, and recovery coefficient (RC) were performed with 3DSlicer. Image quality metrics from an approach called “task-based” were computed with iQMetrix-CT on ⁹⁹mTc visual reconstructions to assess, through spatial frequencies, noise texture in the background (NPS) and contrast restituation of a hot insert (TTF). Spatial resolution indices were calculated from frequencies corresponding to TTF₁₀% and TTF₅₀%.

**Results:** Despite the higher sensitivity of VERITON cameras and the enhanced energy resolution of the V400 (3.2% at 140 keV, 5.2% at 113 keV, and 3.6% at 208 keV), Star-Guide presents comparable image quality. This highlights the need to differentiate sensitivity from count quality, which is influenced by hardware design (collimator, detector block) and conditions image quality as well as the reconstruction process (algorithms, scatter correction, noise regulation). For ⁹⁹mTc imaging, the quantitative image optimization approach based on RCmean for StarGuide versus RCmax for V200 and V400 systems (RCmean/RCmax: 0.9/1.8; 0.5/0.9; 0.5/0.9 respectively—Ø37 mm). SRTB10/50 showed nearly equivalent spatial resolution performances across the different reconstructed images. For ¹⁷⁷Lu imaging, the 113 keV imaging of the V200 and V400 systems demonstrated strong performances in both image quality and quantification, while StarGuide and V400 systems offer even better potential due to their ability to exploit signals from both the 113 and 208 keV peaks. ¹⁷⁷Lu quantification was optimized according to RCmax for all cameras and reconstructions (1.07 ± 0.09—Ø37 mm).

**Conclusions:** The three cameras have equivalent potential for ⁹⁹mTc imaging, while StarGuide and V400 have demonstrated higher potential for ¹⁷⁷Lu. Dedicated visual

<figure><img src="image_3.png" /></figure>

<footnote>*Correspondence:
christopher.hoog@reims.
unicancer.fr</footnote>

<footnote n="1">¹ Medical Physics Department,
Institut Godinot Comprehensive
Cancer Center, Reims, France</footnote>

<footnote n="2">² Department of Diagnostic
Radiology and Nuclear
Medicine, Antoine Lacassagne
Comprehensive Cancer Center,
Université Nice-Côte d'Azur,
33 Avenue de Valombrose,
06189 Nice, France</footnote>

<footnote n="3">³ Department of Medical
Physics, Jean Perrin
Comprehensive Cancer Center,
63000 Clermont-Ferrand, France</footnote>

<footnote n="4">⁴ Department of Nuclear
Medicine and Nancyyclotep
Imaging Platform, CHRU-Nancy,
Université de Lorraine,
54000 Nancy, France</footnote>

<footnote n="5">⁵ Nuclear Medicine Department,
CHU Orleans, 14 Avenue de
l'Hôpital, 45100 Orleans, France</footnote>

<footnote n="6">⁶ Department of Medical Physics,
Georges-François Leclerc Cancer
Center, 1 Rue du Professeur
Marion, 21000 Dijon, France</footnote>

<footnote n="7">⁷ ICMUB, UMR 6302, CNRS, Dijon,
France</footnote>

<footnote n="8">⁸ Centre de Lutte Contre le
Cancer Léon-Bérard, CREATIS
CNRS UMR 5220 INSERM U 1044,
Université de Lyon, INSA-Lyon,
Lyon, France</footnote>

<footnote n="9">⁹ Medical Physics Department,
ICO René Gauducheau, Saint
Herblain 44805, France</footnote>

<footnote n="10">¹⁰ CRCINA, UMR 1232, INSERM,
Nantes, France</footnote>
or quantitative reconstructions offer better specific performances compared to the uni-
fied visual/quantitative reconstruction. The task-based approach appears to be promis-
ing for in-depth comparison of images in the context of system characterization/com-
parison and protocol optimization.

**Keywords:** Nuclear medicine, Molecular imaging, 360° CZT-SPECT/CT cameras, Phantom study, Quantification

**Background**

The introduction of cadmium-zinc-telluride (CZT) semi-conductor detectors during the 2000s led to the first major single photon emission computed tomography (SPECT) technological breakthrough since the initial scintillation-based model developed by Hal Anger in 1957 (A-SPECT) [1].

Due to CZT manufacturing costs and detection limited to low energy photons, com-
mercialization of CZT cameras began with small field of view cameras dedicated to car-
diology applications (c-CZT). In 2007, D-SPECT (Spectrum Dynamics Medical (SDM))
and 2009, Discovery NM530c (General Electric Healthcare (GEHC)), were introduced.
Whilst the NM530c camera is equipped with fixed multi-pin hole collimators, D-SPECT
is designed with several block detectors having parallel-hole collimator and swiveling
detector motion to focus on the heart area. The benefits of these technologies in terms
of sensitivity, spatial and energy resolution, resulted in improved image quality and the
ability to perform dual isotope imaging [2]. In 2016, GEHC introduced the Discovery
NM/CT 670, a general-purpose dual head digital SPECT system equipped with CZT flat
panels (CZT-SPECT). With the ability to image isotopes with energies up to 250 keV,
this camera enabled access to a wider range of conventional nuclear medicine (NM) clin-
ical examinations. CZT technology offered significant improvements in the dose-image
quality trade-off, particularly in the context of planar imaging for which a higher diag-
nostic performance was demonstrated at lower injected activity or acquisition duration
[3–5]. However, some limitations of conventional cameras remained, such as collimator
management, photon loss due to geometry and step-by-step whole-body 3D imaging. In
2017 and 2021 respectively, VERITON (SDM) and StarGuide (GEHC) general-purpose
systems were introduced to the market as a new design of CZT camera called 3D-ring
or 360° CZT-SPECT (360CZT-SPECT) aiming to fully exploit CZT performances and
overcome dual head design limitations.

These new systems consist of twelve detector arms evenly distributed over 360° with a triple detector motion mechanism combining a radial linear motion towards the patient, a ring rotation with up to six angular positions to improve angular sampling and a swiveling motion for better focusing. At the tip of each arm, CZT crystal detectors and their fixed collimator will swivel whilst scanning [6, 7]. This scanning is repeated for each bed position. The fixed collimators were designed to be efficient over a wide energy range depending on the models.

Since the introduction of cardiology-dedicated, flat panel and ring shaped CZT cam-
era designs, multiple phantom studies have been published to assess and compare their
performances, sometimes in comparison to conventional systems [7–12]. Additionally,
clinical studies have validated performances of such cameras for clinical usage [13–18].
For example, Desmonts et al. showed that 360CZT-SPECT had superior sensitivity,
better energy resolution and image contrast than A-SPECT camera, whereas spatial resolution remained similar. The study concluded that the “introduction of this new technology may change current practices in nuclear medicine such as decreasing acquisition time and activity injected to patient” (phantom and clinical study, ⁹⁹mTc, ¹²³I, ²⁰¹Tl, ¹¹¹In) [7]. Carsuzaa et al. [13] showed no significant difference in left ventricular volumes and left and right ventricular ejection fractions between c-CZT- and 360CZT-SPECT performing gated tomographic radionuclide angiography (clinical study, 50 patients). Even the scan intolerance rate due to claustrophobia was explored between A-SPECT and 360CZT-SPECT and showed no significant difference in patient experience [19]. These studies suggested 360CZT-SPECT could replace and even surpass both A-SPECT and c-CZT.

Image quality aside, absolute quantification is one of the key remaining challenges of conventional nuclear medicine. Through studies involving several multi-vendor A-SPECT cameras, Peters et al. highlighted a need for standardization as “close agreement between vendors and sites is key for multi-center dosimetry and quantitative biomarker studies” [20, 21]. Three recent phantom studies aimed to assess the quantitative performances of 360CZT-SPECT cameras within the context of 177-Lutetium (¹⁷⁷Lu) PSMA dosimetry calculation. Danieli and al. [22] and Vergnaud et al. [23] validated the quantification performances of StarGuide and VERITON systems respectively when using optimized reconstruction protocols. While comparing 360CZT-SPECT to conventional cameras, Nuttens et al. [24] showed slightly lower absorbed dose uncertainties in favor of conventional A-SPECT, but all studies agreed this new technology greatly reduced procedure time for whole-body SPECT imaging with around threefold faster scans.

To our knowledge, the three currently available 360° CZT-SPECT/CT cameras have never been compared head-to-head, neither through phantom nor clinical studies. Although NEMA standards are not fully adapted to these cameras (for example, intrinsic mode is unavailable, image sampling is unsuitable for assessing extrinsic spatial resolution), vendor datasheets already exist and have been published [10, 11]. The focus of our study was not on optimization or pure performance assessments. Instead, we aimed to adopt a more clinically oriented approach by performing acquisitions and reconstructions of a customized NEMA IEC body phantom under realistic activity and protocols. The vendors developed their devices and reconstruction parameters using clinical data, particularly in collaboration with the sites selected for this study, Orléans for the Star-Guide and Nancy for the VERITON cameras, thereby enhancing the relevance of our research to clinical conditions. The three cameras were evaluated according to different conventional metrics computed from the acquired spectra and the reconstructed images. Also, we took the opportunity to introduce noise power spectrum (NPS) and task transfer function (TTF) allowing deeper assessments of noise texture and clinical spatial resolution respectively. These metrics are notably involved in an approach called “task-based” dedicated to assessing the detectability of a task function through an index called “d-prime”. The task function is defined by choosing the type of signal to detect, called “clinical task”, and entering its diameter and contrast [25, 26]. This approach is currently used to compare or optimize CT imaging protocols should be helpful in nuclear medicine while addressing shortcomings of NEMA standards.
<figure><img src="image_4.png" /><figcaption>**Fig. 1** Customized NEMA IEC body phantom.</figcaption></figure>

<table><caption>**Table 1** Phantoms preparation.</caption><thead><tr><th></th><th></th><th>StarGuide</th><th>V200</th><th>V400</th></tr></thead><tbody><tr><td rowspan="2"><sup>99m</sup>Tc</td><td>[A<sub>Background</sub>] (kBq/mL)</td><td>10.4</td><td>9.6</td><td>8.4</td></tr><tr><td>Sphere to background ratio</td><td>10.0</td><td>10.0</td><td>10.0</td></tr><tr><td rowspan="2"><sup>177</sup>Lu</td><td>[A<sub>Background</sub>] (kBq/mL)</td><td>78.8</td><td>74.5</td><td>74.9</td></tr><tr><td>Sphere to background ratio</td><td>9.8</td><td>10.0</td><td>10.0</td></tr></tbody></table>

This study focuses on both 99m-Technetium (<sup>99m</sup>Tc), probably the most used isotope in conventional nuclear medicine [27], and <sup>177</sup>Lu which is an extremely challenging radionuclide in terms of theranostics, quantification and dosimetry [28–34].

# Methods

## Cameras

Three 360CZT-SPECT cameras combined with a computed tomography (CT) scanner were evaluated: StarGuide (GEHC, Haifa, Israel) installed in 2020 at the nuclear medicine department of CHU Orléans (Orléans, France); VERITON 200 (V200) and VERITON 400 (V400) (SDM, Caesarea, Israel) respectively installed in 2018 and 2021 at the department of nuclear medicine of CHRU Nancy (Nancy, France). The overall imaging bore of systems is 70 cm for StarGuide and 80 cm for V200 and V400. The VERITON cameras have a 32 cm axial field of view versus 28 cm for StarGuide. The StarGuide and V400 systems have thicker CZT crystal detectors as opposed to V200 (7.25, 7.3 mm and 6 mm respectively). Whilst StarGuide and V400 can acquire photons above 200 keV, V200 detector electronics limit acquisition to 200 keV. V200 and V400 are equipped with the exact same collimator.

## Phantom

A customized NEMA IEC body phantom (PTW, Breisgau, Germany) was used for conventional voxel value-based analyses and innovative task-based image quality assessment. The lung insert was removed and replaced with a fillable cylindrical insert (32 mm diameter x 50 mm height), leading to three distinct zones: “sphere,” “background,” and “cylinder” (Fig. 1). The “sphere” section is dedicated to recovery curves assessments. The “background” section is dedicated to quantification accuracy (Q<sub>error</sub>), noise level and noise texture assessments. The cylinder in the third section simulates a hot lesion on which edge spread function measurements helped in quantifying a clinical spatial
resolution. For each camera, two phantoms filled with ⁹⁹mTc and ¹⁷⁷Lu respectively, were scanned. To mimic clinical conditions, background concentrations of 10 kBq/mL for ⁹⁹mTc and 75 kBq/mL for ¹⁷⁷Lu were defined. The spheres and the cylinder were filled with a more concentrated radioactive solution to achieve a 10:1 sphere to background ratio (Table 1) following the stock solution method filling one tenth of the background of the phantom (volume defined by weighted with a precision balance).

## Image acquisition & reconstruction

Positioning of the phantom and scan acquisitions were consistent across all cameras with each phantom positioned flat on the examination table and precisely aligned within the CZT detectors' central axial field of view. With the StarGuide system, table height was automatically set-up, whilst for VERITON, table height was manually adjusted using laser alignment. Prior to SPECT data acquisition, X-ray scout views and CT scans were performed to validate correct positioning of the phantoms. These scans provided both anatomical imaging and µ-map for attenuation correction (CTAC). Subsequently, ten-minute list mode acquisitions were performed, adhering to routine clinical protocols for both CT imaging and nuclear medicine (NM) data collection, as outlined in Table 2. Energy spectra and ten-minute NM reconstructions were generated from list-mode data files.

In the clinical setting, manufacturers provide the ability to perform reconstructions that are optimized for diagnostic quality and/or enhanced quantitative accuracy. We therefore requested both types of reconstructions, depending on the specifications provided by respective manufacturers. In the case of the ¹⁷⁷Lu-phantom, it's worth mentioning that both 113 keV and 208 keV peaks were accessible for StarGuide and the V400 systems, whereas the V200 camera was constrained to the 113 keV peak only.

<table><caption>**Table 2** Clinical protocols used for CT imaging and NM acquisitions.</caption><thead><tr><th></th><th></th><th>StarGuide</th><th>V200</th><th>V400</th></tr></thead><tbody><tr><td>CT</td><td></td><td>Helical 0.80 s; Pitch 1.375; 120 kV; 80.0 mA<br>CTDI vol.: 4.12 mGy</td><td>Helical 0.67 s; Pitch 1; 120 kV; 80.4 mAs</td><td></td></tr><tr><td>NM</td><td>Duration</td><td>10'00" + 30 s (rotation)</td><td>CTDI vol.: 5.58 mGy</td><td></td></tr><tr><td></td><td>Rotation</td><td>4 angles</td><td>10'00" + 30 s (rotation)</td><td></td></tr><tr><td>⁹⁹mTc</td><td></td><td>140 keV<br>Lower scatter: [114–126] keV<br>Photopeak: [126–154] keV (140±10%)</td><td>Lower scatter: [109–130] keV<br>Photopeak: [130–151] keV (140±7,5%)</td><td></td></tr><tr><td>¹⁷⁷Lu</td><td></td><td>113 keV<br>Lower scatter: [92.1–100.9] keV<br>Photopeak: [101.7–124.3] keV (113 ± 10%)<br>Upper scatter: [125.1–134.2] keV</td><td>Lower scatter: [79–101.6] keV<br>Photopeak: [101.6–124.2] keV (112.9 ± 10%)<br>Upper scatter: [124.2–146.8] keV</td><td></td></tr><tr><td></td><td></td><td>208 keV<br>Lower scatter: [175.8–194.3] keV<br>Photopeak: [195.5–220.5] keV (208±6%)</td><td>–</td><td>Lower scatter: [161.6–192.8] keV<br>Photopeak: [192.8–224] keV (208 ± 7.5%)<br>Upper scatter: [224–255] keV</td></tr></tbody></table>
All 2.46 mm voxel size reconstructions were performed using ordered subset expectation maximization (OSEM) or QClear, a Bayesian penalized likelihood (BPL) reconstruction algorithm using block-sequential regularized expectation maximization (BSREM) [35]. CTAC was applied on every reconstruction. Optional scatter correction (nSC/SC) was applied using dual/triple energy window methods (DEW/TEW) depending on isotope and peak: DEW for ⁹⁹mTc 140 keV (GEHC) and ¹⁷⁷Lu 208 keV (GEHC); TEW for ¹⁷⁷Lu 113 keV (GEHC-SDM) and 208 keV (SDM-V400). Point Spread Function Recovery (PSFR), here called Resolution Recovery (RR) was systematically used for GEHC reconstructions and optionally used for SDM reconstructions. It is worth noting that SDM’s RR is based on the system response to a point source scanned successively in air and in a scatter media. This empirical model will therefore correct aberrations due to the system’s elements (collimator, crystal...) but as the model is based on actual experimental acquisition, will also include Compton scattering effects. In a first approximation, this scattering correction is robust enough for ⁹⁹mTc for which most user opt to apply RR only. For ¹⁷⁷Lu, for which the scatter fraction is more important due to down scatter from the 208 keV peak, scatter correction included in RR results in a more pronounced under correction and most user comply with SDM guidelines to use the triple energy window-based scatter correction. Therefore, to differentiate the methodology for SC is always specified either as SC(DEW/TEW) or SC(RR). To avoid over-correction, both types cannot be applied together. Noise regulation (NR) is performed through relative difference penalty (RDP) [35] and Clarity3D for StarGuide and intra- and post-iteration filtering for VERITON cameras.

For ⁹⁹mTc, distinct reconstructions dedicated to visualization and quantification were provided for all three cameras. The visual reconstruction for StarGuide was based on QClear AC nSC NR, while the quantitative reconstruction was based on OSEM AC SC(DEW) nNR, resulting in a significant difference in image quality. Both visual and quantitative reconstructions for the VERITON systems were OSEM AC SC(RR) NR. The V200 and V400 quantitative reconstructions differed from the visual ones only by the number of subsets (8 vs. 32).

For ¹⁷⁷Lu, StarGuide provided visual/quantitative reconstructions for the 113 keV and 208 keV peaks, based on QClear AC SC(TEW/DEW) NR. To fully exploit the recorded data, GE recommend generating an image as the voxel-wise arithmetic sum of the images obtained from the two peaks. For the 113 keV peak of V200 and V400, the visual image was AC nSC NR, while the quantitative image was AC SC(TEW) NR. V400 did not provide a separate image for the 208 keV peak but offered a combined 113-208 keV image considered both visual and quantitative. This combined image is the average of a reconstruction of the 113 keV peak AC SC(TEW) NR and a reconstruction of the 208 keV peak AC SC(RR) NR (independent images were not available for this study).

## Quantification

All injected activities were measured using on-site dose calibrators: Capintec CRC15R in Orléans and Capintec CRC-25 in Nancy. For ⁹⁹mTc, both dose calibrators were initially certified by the French National Laboratory "Henri Becquerel" (LNHB). For ¹⁷⁷Lu, vial and syringe calibration factors were established following LNHB guidelines, using a ¹⁷⁷Lu source provided by Advanced Accelerator Applications (Saint Genis Pouilly,
France). Both dose calibrators are subject to a strict quality insurance policy according to French legislation. Acceptance tests include accuracy, reproducibility, linearity and geometry response. Daily controls consist of background check and constancy of the response with a long half-life check source. The test for constancy of the response is performed monthly with two long half-life check sources. No volume correction factor was calculated for ¹⁷⁷Lu.

Both manufacturers achieved absolute quantification through a cross-calibration methodology, which involves acquiring data from a cylindrical phantom containing a homogeneous radioactive solution with a known activity concentration, as determined by a dose calibrator. The determination of a calibration factor for each specific isotope is computed as the average count observed in the phantom's uniform background (spherical VOI 80% phantom diameter) divided by the time duration and the activity concentration at the time of acquisition. The calibration factors are defined for quantitative imaging only and involve the dedicated reconstruction algorithm.

For the ¹⁷⁷Lu isotope, StarGuide produces images for both the 113 keV and 208 keV energy peaks, requiring the computation of distinct calibration factors for each of these peaks. In contrast, with the V200 and V400 systems, a calibration factor is solely computed for the 113 keV energy peak. The V400 system enables quantitative imaging by combining data from both the 113 keV and 208 keV peaks. To reach consistency in the average signal within the homogeneous background, a normalization factor for the 208 keV peak is derived from the 113 keV image. All calibration factors were verified, and updated if required, prior to performing the phantom acquisitions for this study.

## Analysis

### Energy resolution and volumetric sensitivity from spectra

For a relevant comparison, the energy spectra obtained from raw data were resampled with a 1 keV step and normalized in kcps/(MBq/mL) considering the 600 s acquisition duration and the activity concentration at the time of acquisition. The energy resolution of each exploitable peak was calculated as the ratio of the full width at half-maximum (FWHM) to the measured energy peak. Furthermore, a volumetric sensitivity value was calculated by integrating the counts over the photopeak energy window normalized by acquisition duration and activity concentration.

### Image quality and quantification accuracy assessment from reconstructed images

Quantitative analyses using conventional metrics were conducted using the 3DSlicer (v5.2.2) software. After processing a NM-CT registration (X-Y-Z translations), spherical volumes of interest (VOI) and a cylindrical VOI (about 250 cm³) were defined on the CT images to match the internal diameter of the spheres (Fig. 2a red VOIs) and the homogeneous background respectively (Fig. 2a green VOIs). From NM reconstructions, the maximum and mean values of each sphere were calculated, as well as the mean and standard deviation values in the homogeneous background. Using those measurements, the following metrics were calculated (Table 3):

- Noise level based on the standard deviation and mean voxel value measured in the background.
<figure><img src="image_5.png" /><figcaption>**Fig. 2** Illustration of voxel value-based metrics measurements from 3DSlicer (a), task-based quality image assessment with iQMetrix-CT (b).</figcaption></figure>

<table><caption>**Table 3** Formula/metrics and analysis software.</caption><thead><tr><th></th><th>Formula/Metric</th><th>Phantom section</th><th>Software</th><th>Images</th></tr></thead><tbody><tr><td>Noise</td><td>Noise level (%) = 100 * <sup>SD<sub>background</sub></sup>&frasl;<sub>Mean voxel value<sub>background</sub></sub></td><td>Background</td><td>3DSlicer</td><td>All images</td></tr><tr><td>Spatial Resolution</td><td>NPS; f<sub>mean</sub>; f<sub>max</sub><br/>TTF; SR<sub>TB10</sub> = 1/f(TTF<sub>10%</sub>); SR<sub>TB50</sub> = 1/f(TTF<sub>50%</sub>)</td><td>Background<br/>Cylinder</td><td>iQMetrix-CT<br/>iQMetrix-CT</td><td>All images<br/><sup>99m</sup>Tc—Visual</td></tr><tr><td>Quantification</td><td>Q<sub>error</sub>(%) = 100 * (<sup>Mean signal background</sup>&frasl;<sub>Activity concentration<sub>background</sub></sub> - 1)</td><td>Background</td><td>3DSlicer</td><td><sup>99m</sup>Tc—Quant<br/><sup>177</sup>Lu—Quant.<br/>and Visual/Quant.</td></tr><tr><td>Recovery coefficient</td><td>= <sup>Max or Mean voxel value<sub>sphere</sub></sup>&frasl;<sub><sup>Mean voxel value<sub>background</sub></sup>&frasl;<sub>Activity concentration<sub>sphere</sub></sub></sub></td><td>Sphere &amp; Background</td><td>3DSlicer</td><td><sup>99m</sup>Tc—Quant<br/><sup>177</sup>Lu—Quant.<br/>and Visual/Quant.</td></tr></tbody></table>

- Q<sub>error</sub> based on the mean voxel value measured in the background and the true activity concentration in the background.

- Recovery coefficient of each sphere based on the mean (RC<sub>mean</sub>) or maximum (RC<sub>max</sub>) voxel value measured for each sphere, the mean voxel value measured in the background, and the true activity concentrations both in the spheres and background.

Inspired from the “task-based” image quality assessment approach currently used to compare or optimize CT imaging protocols, we introduced NPS and TTF to assess noise texture in the background and contrast restitution of a cylindrical insert mimicking an anatomical specific density (CT) or in our case a lesion uptake. From the radial profile of the 2D Fourier transform of a homogeneous image, the NPS quantifies both noise amplitude and texture (Fig. 3a) and helps identify structures and patterns in homogeneous images [36]. TTF is computed as the 1D Fourier transform of the derivative edge spread function (ESF) obtained between the center of the cylinder and the background (Fig. 3b). NPS and TTF were performed using the iQMetrix-CT software (v1.1) [25] (Fig. 2b, Table 3):
<figure><img src="image_6.png" /><figcaption>**Fig. 3** Illustration of NPS (a) and TTF (b) estimations from phantom homogeneous background and a cylindrical insert mimicking a lesion uptake.</figcaption></figure>

- The normalized NPS ($n$NPS) curves were calculated from 4 square regions of interest (automatically sized) duplicated on 5 consecutive axial slices within the homogeneous region. This allowed for a comparison of noise texture, particularly in terms of peak frequency ($f_{peak}$) and average frequency ($f_{mean}$).

- The TTF was evaluated from a circular region of interest (automatically placed) duplicated on 3 consecutive axial slices around the cylindrical insert. According to AAPM Report 223 [26], a CNR value greater than 15 between the cylinder and background must be achieved for a meaningful TTF. The TTF calculation was performed based on an unconditioned and unsymmetrized Edge Spread Function (ESF) obtained by the "pixel distance" method, and a filtered Line Spread Function (LSF) using the Hann filter. Spatial resolution indices based on the clinical task ($SR_{TB}$) were calculated as the inverse of the frequencies corresponding to 10% and 50% of the TTF maximum intensity (Table 3).

Noise level was assessed on every reconstruction. $Q_{error}$ was quantified on dedicated quantitative reconstructions (quant and visual/quant.). RC curves were only deducted from quantitative and visual/quantitative images. TTF was only applied on the $^{99m}$Tc visual reconstructions as it was the only case that satisfied a CNR superior to 15 between insert and background.

# Results

## Energy resolution & volumetric sensitivity from energy spectra

Figure 4 shows the resampled spectra and Table 4 the results of their analysis. All three cameras exhibited a peak around 60 keV, originating from the tungsten collimator fluorescence. However, this peak was higher for V200, especially for the $^{177}$Lu phantom. It should be noted that the apparent peak of V200 does not represent the information from 208 keV photons; all the information measured beyond 200 keV is indeed re-indexed between 200 and 250 keV.

For $^{99m}$Tc, peak position was measured on the three cameras at 140.5 keV, 140.7 keV and 141.3 keV on StarGuide, V200 and V400 respectively. For $^{177}$Lu, all three systems measured the 113 keV peak within 1 keV accuracy and the 208 keV at 210 keV on
<figure><img src="image_7.png" /><figcaption>**Fig. 4** Energy spectra recorded from the acquisitions of ⁹⁹mTc (left) and ¹⁷⁷Lu (right) NEMA IEC body phantoms. The energy spectra were resampled with a 1 keV step and normalized in kcps/(MBq/mL).</figcaption></figure>

<table><caption>**Table 4** Energy spectra analysis.</caption><thead><tr><th></th><th>StarGuide</th><th>V200</th><th>V400</th></tr></thead><tbody><tr><td>Theoretical peak (keV)</td><td>140.5</td><td>113.0</td><td>208.0</td></tr><tr><td>Measured peak (keV)</td><td>140.5</td><td>114.0</td><td>210.0</td></tr><tr><td>Delta peak (keV)</td><td>0.0</td><td>1.0</td><td>2.0</td></tr><tr><td>FWHM (keV) *</td><td>8.8</td><td>11.7</td><td>12.1</td></tr><tr><td>Measured energy resolution (%)</td><td>6.2</td><td>10.3</td><td>5.7</td></tr><tr><td>NEMA energy resolution (%)—Datasheet [10;11]</td><td>5.4</td><td>7.5</td><td>4.6</td></tr><tr><td>Measured volumetric sensitivity (kcps/(MBq/mL))</td><td>499</td><td>72</td><td>74</td></tr><tr><td>NEMA volumetric sensitivity (kcps/(MBq/mL)) — Datasheet [10;11]</td><td>542</td><td>—</td><td>—</td></tr></tbody></table>

StarGuide and 210.8 keV on V400. These results do not reflect an intrinsic characteristic of the cameras as they depend on environmental factors and peaking calibration.

In terms of energy resolution, StarGuide achieved a 6.2%, 10.3% and 5.7% energy resolution for peak 140 keV (⁹⁹mTc), 113 keV and 208 keV (¹⁷⁷Lu) respectively. V200 achieved a 5.8% and 9.0% energy resolution for peak 140 keV (⁹⁹mTc) and 113 keV (¹⁷⁷Lu) respectively. V400 achieved a 3.2%, 5.2% and 3.6% energy resolution for peak 140 keV (⁹⁹mTc), 113 keV and 208 keV (¹⁷⁷Lu) respectively.

StarGuide offered a volumetric sensitivity of 499, 72 and 74 kcps/(MBq/mL) at 140 keV (⁹⁹mTc), 113 keV and 208 keV (¹⁷⁷Lu) respectively. V200 offered a volumetric sensitivity of 764 and 170 kcps/(MBq/mL) at 140 keV (⁹⁹mTc) and 113 keV (¹⁷⁷Lu) respectively. V400 offered a volumetric sensitivity of 919, 165 and 285 kcps/(MBq/mL) at 140 keV (⁹⁹mTc), 113 keV and 208 keV (¹⁷⁷Lu) respectively.

## Image quality and quantification accuracy assessment from reconstructed images

### ⁹⁹mTc

With all three cameras, the four largest spheres are clearly resolved on both visual and quantitative reconstructions, the fifth sphere appears with low contrast but with a better definition on V200, and the smallest sphere was not visible (Fig. 5Aa–f). When focusing on visual reconstructions, VERITON cameras offered a more conventional noise texture and relevant spheres size whereas the background appeared smoother and the

<footnote>* Because of the scatter level on StarGuide and V200, the FWHM of 113 keV peak (177Lu) was estimated as the double of the superior part of the FWHM</footnote>
<figure><img src="image_8.png" /><figcaption>**Fig. 5** Visual (a–c) and quantitative (d–f) reconstructions from ten-minute acquisitions of the ⁹⁹mTc (A) and ¹⁷⁷Lu (B–D) NEMA IEC body phantoms (spheres mid-plane) on StarGuide, V200 and V400 cameras. The images are displayed with a contrast set at 50% of the maximum. The algorithm for each image is specified (OSEM: Ordered Subset Expectation Maximization) and reconstruction parameters (AC: Attenuation Correction; SC: Scatter Correction; RR: Resolution Recovery; NR: Noise Regulation; n-: non-; DEW: Double Energy Window; TEW: Triple Energy Window).</figcaption></figure>

spheres larger on StarGuide (Fig. 5Aa–c). Regarding quantitative reconstructions, all images appeared noisier than visual ones. With StarGuide we observed a difference in background pattern between the center and the phantom's edges, as well as deformed spheres (Fig. 5Ad), whilst V200 and V400 exhibited the same background texture and appearance of the spheres (Fig. 5Ae–f) on quantitative and visual images.

StarGuide led to the lowest and highest noise level in the background for visual QClear and quantitative OSEM reconstructions, with values of 7% and 34% respectively. V200 allowed a slightly lower noise level compared to V400 for both visual (12% vs. 15%) and quantitative (21% vs. 26%) reconstructions. VERITON noise level difference between visual and quantitative reconstructions was less accentuated than on StarGuide (Fig. 6Aa)
<figure><img src="image_9.png" /><figcaption>**Fig. 6** Conventional metrics for ⁹⁹mTc (A) and ¹⁷⁷Lu (B) phantoms: Noise level (a) and Qerror (b) were measured in the homogeneous background section. RC mean and max curves (c) were displayed for quantitative reconstructions. On histograms, black outlines illustrate quantitative reconstructions (dotted outlines for visual/quant. reconstructions). N/A stands for Not Applicable.</figcaption></figure>

<figure><img src="image_10.png" /><figcaption>**Fig. 7** Noise power spectrum (NPS) (a) and task transfer function (TTF) (b) from the ⁹⁹mTc-phantom and NPS (c) from the ¹⁷⁷Lu-phantoms. NPS and TTF are computed from the background and cylinder section of the phantom respectively.</figcaption></figure>

StarGuide offered a quantification accuracy within 0.1% in the background of the OSEM SC quantitative image. Quantification error was about 3.3% and 2.9% for quantitative reconstructions of V200 and V400 cameras respectively (Fig. 6Ab).

As shown with RC curves obtained from quantitative reconstructions (Fig. 6Ac), on StarGuide we measured RC<sub>mean</sub> values of 0.77, 0.86, and 0.90 for the Ø22 mm, Ø28 mm, and Ø37 mm spheres respectively and RC<sub>max</sub> exceeded 1.00 for the Ø17 mm sphere, ranging from 1.83 to 2.31 for larger spheres. The V200 and V400 cameras showed similar performances, converging to 0.5 (RC<sub>mean</sub>) and 1.0 (RC<sub>max</sub>) from the Ø22 mm sphere.

The six nNPS curves of both visual and quantitative reconstructions from the three cameras had the same peak frequency at 0.025 mm⁻¹. The average frequencies between 0.037 and 0.041 mm⁻¹ also indicated an equivalent noise texture across all reconstructions, except for the quantitative reconstruction from StarGuide, which showed a different visual aspect translated with an average frequency of 0.047 mm⁻¹ (Fig. 7a)
The TTF curves of the three visual reconstructions were quite similar. We computed SR<sub>TB10</sub>/SR<sub>TB50</sub> values of 14.7/26.2, 12.9/23.7, and 13.7/24.6 mm for the StarGuide, V200, and V400 respectively (Fig. 7b).

¹⁷⁷Lu

For 113 keV peak imaging, the visual/quantitative reconstructions from StarGuide pre-
sented artifacts and only allowed to discern four distorted spheres (Fig. 5Ba,d). The nSC
nRR visual images from the V200 and V400 displayed better quality with a more homo-
geneous background and better geometric restitution of the five visible spheres (Fig. 5Bb,
c). Due to the scatter correction, quantitative images of V200 and V400 appeared noisier,
but still displayed five visible spheres with a better contrast (Fig. 5Be, f).

The StarGuide camera was able to generate a 208 keV energy window centered image without background artifact where all five spheres were visible (Fig. 5Ca, d).

The StarGuide and V400 generated visual/quantitative images combining both 113 keV and 208 keV peaks (Fig. 5D). These images had a comparable image quality, with a noise—detectability tradeoff allowing the five spheres to be visualized with a homogeneous background.

StarGuide's visual/quantitative reconstructions led to a noise level of 32% and 23% for 113 keV and 208 keV imaging respectively. V200 and V400 reconstructions for 113 keV peak, led to the same noise level of 11% for visual images and 42% (V200)–52% (V400) for quantitative images. The StarGuide reconstruction obtained from the voxel-wise arithmetic sum of the images of the two peaks led to a noise level of 20%, which is close to the 18% obtained for the visual/quantitative 113–208 keV combined reconstruction from the V400 camera (Fig. 6Ba).

On the three StarGuide reconstructions (113 keV, 208 keV and 113-208 keV), we observed a quantitative overestimation of almost 15% in the background. V200 and V400 113 keV dedicated quantitative reconstructions led to a Q<sub>error</sub> of -1.7% and -4.0% respectively, whilst we measured a Q<sub>error</sub> of 7.9% on the V400 combined 113-208 keV visual/quantitative reconstruction (Fig. 6Bb).

For visual and visual/quantitative reconstructions (StarGuide 113 keV, 208 keV and 113-208 keV; V400 113 and 208 keV), the recovery curves were quite close to each other, increasing between Ø10 mm and Ø37 mm from 0.12±0.02 to 0.56±0.40 and 0.14±0.02 to 1.03±0.10 for RC<sub>mean</sub> and RC<sub>max</sub> values respectively. The 113 keV reconstructions of the V200 and V400 dedicated quantitative images offered better accuracy with regards to the 1.00 SUV target value, especially on all the intermediate spheres (Fig. 6Bc).

The nNPS curves showed quite homogeneous noise textures between the reconstruc-
tions with the same peak frequency of 0.025 mm⁻¹ and mean frequencies between 0.038
and 0.041 mm⁻¹. However, we observed a trend with the curves of the VERITON cam-
eras which looked hollower towards the low frequencies versus the more rounded curves
of the StarGuide, thus including higher frequencies (Fig. 7c).

Discussion

Through an original phantom-based study, we established a twofold comparison of
StarGuide, V200 and V400 360CZT-SPECT cameras. The first comparison criterion,
based on energy spectra analysis, showed VERITON cameras were more sensitive
than StarGuide and V400 provided enhanced energy resolution. The second one, based on reconstructed images using clinical protocols, demonstrated the potential of the cameras in terms of image reconstruction and highlighted the different approaches to quantification of ⁹⁹mTc.

## Customized phantom design

The introduction of a customized NEMA IEC body phantom where the cold lung was replaced by a hot cylinder enabled both conventional and innovative image quality and quantification accuracy assessments (Fig. 1). We improved this approach from a previous study comparing OSEM and xSPECT algorithms (Siemens Healthineers, Erlangen, Germany) [37], where TTF was only performed from the mid-plane of the Ø37 mm sphere. The introduction of the cylinder centered in the field of view enabled computation of the TTF from several slices without axial partial volume effect and limiting target deformation. According to SDM ⁹⁹mTc datasheets [11], spatial resolution in presence of scatter medium is less than 4.5 mm so we assume our 32 mm diameter cylinder was not significantly impacted by transaxial partial volume effect. However, measurement reproducibility and influence of the cylinder diameter in the relevance of TTF should be studied further. Bailey et al. [38] recently introduced a 70 mm diameter cylinder, compatible with NEMA IEC body phantom, dedicated to assessing the quantification accuracy of long period nuclides. This cylinder could be more adapted to TTF measurements, especially considering ¹⁷⁷Lu and medium energy collimator that degrades spatial resolution. Moreover, the activity concentration within the cylinder should be increased to ensure a CNR higher than 15, which was not reached for these ¹⁷⁷Lu-phantom acquisitions.

## Energy resolution and system volumetric sensitivity from spectra

Analyses of the energy spectra showed the energy resolution of StarGuide and V200 were equivalent, but twice higher for V400 (Fig. 4, Table 4). While StarGuide and V400 have similar thick CZT crystals (within 0.05 mm), the higher energy resolution of V400 could be explained by different parameters such as crystal growing technique, whole detector bloc design, high voltage value or electronic signal processing.

The lower volumetric sensitivity of StarGuide could not be justified by the 4 cm shorter axial FOV since the phantom entirely fitted within one bed position for the three cameras. Hence, it ostensibly comes from the collimator design between the two vendors associated with the CZT crystal, electronic design, and signal processing. The sensitivity - spatial resolution tradeoff due to collimator design is a foundational concept of SPECT imaging. We were unfortunately unable to assess or compare collimator designs due to non-disclosure of the VERITON collimator specifications by SDM.

Despite different phantoms and measurement conditions, the measured energy resolution and volumetric sensitivity were in accordance with the manufacturers' datasheets (Table 4) [10, 11] based on NEMA standards, for both ⁹⁹mTc and ¹⁷⁷Lu radionuclides. Our results were also relevant with regards to the Desmonts et al. study on V200 system, presenting a 5.5% energy resolution in air and volumetric sensitivity measurement of 65.8 cps/MBq using a uniformly filled with radioactive solution body phantom [7].

SDM has recently released a V300 camera allowing photon detection up to 300 keV and equipped with 5 mm thickness CZT crystals (6 mm and 7.3 mm for V200 and
V400 respectively) and the exact same collimator as V200 and V400 cameras, thus demonstrating that crystal thickness is not the only limiting factor in terms of high energy constraints, and that the whole detection chain, including electronic design and signal processing also play a crucial role in terms of detector performances.

## Reconstruction protocol approach

Description of the different reconstructions (Fig. 5) has highlighted the manufacturers’ strategies for providing the best reconstructions dedicated to visualization and/or quantification, based on their respective software developments:

- For ⁹⁹mTc, GEHC developed separate reconstructions, optimized for visualization (Q.Clear AC nSC) and quantification (OSEM AC SC). Both reconstruction defaults are available in the system for the reader to use per the required clinical task. Alternatively, VERITON cameras offer both visual and quantitative OSEM SC(RR) reconstructions, the second reconstruction having more updates than the first (Fig. 5A).

- For ¹⁷⁷Lu theranostic images, GE followed the PET approach, generating diagnostic QClear SC images that also allow quantification. On the other hand, SDM proposes an OSEM nSC reconstruction for the 113 keV peak that offers better visualization comfort (lower noise level); and noisier quantitative OSEM SC(RR) reconstruction that offers recovery coefficients closer to the target value of 1.00 (RC<sub>max</sub>). Finally, the combined 113-208 keV visual/quantitative images from StarGuide and V400 provided the best tradeoff between image quality and quantification. If 113 keV images from V200 and V400 could be fully exploited, this study showed it was not the case with StarGuide, for which the 113-208 keV combined image is the best to be exploited (Fig. 5D)].

## Image quality and quantification accuracy assessment from reconstructed images

Image quality is inherently linked with energy resolution and sensitivity, but this relationship is greatly influenced by hardware design (collimator, detector block), which defines the "count quality". Additionally, acquisition and reconstruction parameters also impact image quality. This explains why, when comparing different systems, it is essential to decouple energy and sensitivity results from image quality. For example, the StarGuide, despite having the lowest sensitivity, exhibited the best SNR for visual reconstruction of ⁹⁹mTc. The aim of this study was to work under clinical conditions that integrate both thin notion of "count quality" and the practical use of the devices.

Analysis of the conventional metrics (noise level, Q<sub>error</sub>, RC) (Fig. 6) highlighted that scatter correction should be disabled for visualization purposes (lower noise level). All quantitative reconstructions involving scatter correction led to an accurate quantification in the background (Q<sub>error</sub> < 5%) except for a 15% Q<sub>error</sub> for ¹⁷⁷Lu-StarGuide reconstructions. However, this last result was not observed in the Danieli et al. [22] study showing that the quantification accuracy of the StarGuide system, although affected by septal penetration, was < 10% for all ¹⁷⁷Lu reconstructions.
We also demonstrated the importance of analyzing RC curves to understand the impact of the partial volume effect on quantification accuracy based on lesion size. For StarGuide, the ⁹⁹mTc quantitative reconstruction was optimized according to RC<sub>mean</sub>, as GEHC considers RC<sub>max</sub> values are too dependent on noise. For other cases, (StarGuide ¹⁷⁷Lu, VERITON ⁹⁹mTc and ¹⁷⁷Lu), we clearly showed the optimization was based on RC<sub>max</sub> values. In their study comparing ⁹⁹mTc quantification performances of several A-SPECT cameras, Peters et al. showed median RC value of sphere Ø37 mm converged to 0.9 (RC<sub>mean</sub>) and 1.2 (RC<sub>max</sub>) [20]. Using RC curves, Tran-gia et al. suggested a partial volume effect correction method in the context of quantitative ¹⁷⁷Lu SPECT/CT imaging [39]. Finally, RC<sub>mean</sub> values were estimated from CT-based VOI, therefore without considering deformation on metabolic images. Different studies have explored the impact of the segmentation method for the quantification of spheres, organs, or lesions [20, 23, 37].

Concerning innovative metrics (Fig. 7), nNPS curves showed a quite equivalent noise texture of the images according to the cameras and reconstructions, except for StarGuide ⁹⁹mTc quantitative reconstruction. Indeed, the visibly different pattern between the center and the edges of the phantom was restituted through a nNPS curve including higher spatial frequencies. TTF and SR<sub>TB</sub> enabled direct comparison of spatial resolution between the three cameras through a clinical approach. No significant difference was found between the three cameras with SR<sub>TB10</sub> and SR<sub>TB50</sub> values ranging from 12.9 to 14.7 and 24.6 to 26.2 mm respectively. The datasheets following NEMA standards point out the three cameras state a “central reconstructed spatial resolution with a scattering medium of less than 4.5 mm” [10, 11]. If datasheets focus on achieving best spatial resolution using a filtered back projection reconstruction algorithm [40], TTF method is a promising approach to computing a more clinical-like spatial resolution. Whilst the potential of innovative metrics has been illustrated here, our final objective would be to achieve the entire task-based image quality assessment approach computing a relevant detectability index d-prime that would surpass the conventional CNR.

## Perspectives

Through the multiple exchanges we had with the manufacturers, we clearly felt 360CZT-SPECT is still a very recent technology with a lot of improvements to come from hardware and software developments. In particular, the actual energy window inherited from conventional A-SPECT should be adjusted to the energy resolution; as an example, the 15% energy window width does not fit the 3.6% improved energy resolution of the V400-208 keV peak (Tables 2 and 4). Also, the PET approach offering a single visual and quantitative image should be preferred. The manufacturers of ring cameras also state that their fixed collimators will not prevent scanning high energy isotopes such as ¹³¹I, as future software developments will algorithmically correct for septal penetration.

¹⁷⁷Lu-labelled pharmaceutical guidelines have not yet been updated regarding quality control [40] and dosimetry for this technology. Indeed, EANM committee recommendations for dose estimation are to use 208 keV peak based images from an A-SPECT camera equipped with a medium energy collimator [41]. This appears to be irrelevant
when using 360CZT-SPECT cameras as they include a multi energy fixed collimator and because V200 is limited to 113 keV photon energy. Thus, it seems essential to perform clinical assessments of coming new developments, analog to Vergnaud et al. validating the use of V200 for ¹⁷⁷Lu monitoring only using the 113 keV peak [23].

## Limitation

Despite being aware of the potential bias induced by statistical differences in term of accrued counts, we opted to comply with NEMA methodology that defines a scan time and specific background activity. With the ⁹⁹mTc-phantom, only unexpected manipulation delay prevented us to remain within the ±5% activity stipulated by the standard. However, we assume the variation of activity concentration in the background did not significantly impact our results.

Our study faced other several limitations. First, it was limited to two types of radionuclides, and we assumed the dedicated clinical protocols were optimized for this study. Then, nAC imaging was not evaluated, whereas it is widely practiced for ⁹⁹mTc on non-oncological indications, where use of CT is not considered clinically required due to ALARA principles. Also, some ⁹⁹mTc protocols also look for “cold lesions” such as in cardiac imaging, but our phantom did not contain a cold insert. Finally, specific imaging modes such as focus mode [7, 42] or enhanced reconstructions dedicated to bone scans [43, 44] were not explored.

## Conclusion

For the first time, three 360CZT-SPECT cameras have been compared through a phantom-based study under clinical conditions. From a unique acquisition, volumetric sensitivity and energy resolution were computed from raw spectra while conventional and innovative metrics ensured an objective description of reconstructed images following the vendor's recommended approach.

We highlighted that VERITON cameras were more sensitive than StarGuide and V400 provided enhanced energy resolution. However, all three cameras had equivalent potential for ⁹⁹mTc imaging, while StarGuide and V400 had higher potential than V200 for ¹⁷⁷Lu imaging thanks dual 113-208 keV peak imaging. We showed that dedicated visual or quantitative reconstructions offered better specific performances compared to the single visual/quantitative reconstructions inspired from PET imaging. This study did not provide an exhaustive evaluation as it was limited to two isotopes, and because nAC reconstructions, cold lesions and specific modes were not covered.

## Abbreviations

¹⁷⁷Lu 177-Lutetium

⁹⁹mTc 99m-Technetium

aFOV Axial field of view

AC Attenuation correction

BSREM Block-sequential regularized expectation maximization

CT Computed tomography

CZT Cadmium zinc telluride

DEW Double energy window

GEHC General electric healthcare

MTF Modulation transfer function

MRT Molecular radiation therapy
<table><tr><td>NM</td><td>Nuclear medicine</td></tr><tr><td>NPS</td><td>Noise power spectrum</td></tr><tr><td>NR / nNR</td><td>Noise regulation / non noise regulation</td></tr><tr><td>OSEM</td><td>Ordered subset expectation maximization</td></tr><tr><td>PET</td><td>Positron emission tomography</td></tr><tr><td>PSF</td><td>Point spread function</td></tr><tr><td>QC</td><td>QClear</td></tr><tr><td>RDP</td><td>Relative difference penalty</td></tr><tr><td>RR / nRR</td><td>Resolution recovery / non resolution recovery</td></tr><tr><td>SC / nSC</td><td>Scatter correction / non scatter correction</td></tr><tr><td>SDM</td><td>Spectrum dynamics medical</td></tr><tr><td>SPECT</td><td>Single photon emission tomography</td></tr><tr><td>TEW</td><td>Triple energy window</td></tr><tr><td>TTF</td><td>Task transfer function</td></tr><tr><td>V200</td><td>VERITON 200</td></tr><tr><td>V400</td><td>VERITON 400</td></tr></table>

## Acknowledgement

This research was conducted within the context of an "invitation to tender" under the auspices of UNICANCER for the 360° CZT cameras lot. We thank the individuals and organizations that played a pivotal role in the success of this study. We appreciate UNICANCER's role in managing the market and their guidance throughout the study, which provided a foundation for our work. We express our kind appreciation to the medical and paramedical teams at CHRU Nancy and CHU Orléans for providing access to the necessary equipment and assisting in the measurement procedures. Their support significantly contributed to the successful completion of this research. We thank General Electric Healthcare and Spectrum Dynamics Medical for generously funding our physicists' travel expenses. General Electric Healthcare also sponsored the 177Lu source for the StarGuide assessment in Orléans. Finally, we would like to recognize the valuable insights gained from collaborative discussions with the teams of General Electric Healthcare and Spectrum Dynamics Medical. These exchanges significantly enriched the discussion in our study. Finally, we would like to thank Yves Barbot-teau, developer of IQMetrix-CT, who helped us adapt this software for nuclear medicine practice.

## Author contributions

CH, P-MK, LF, J-NB, NS and RP formed an expert group in the context of an invitation to tender managed by UNICANCER. They discussed the phantom design and preparation, and the different measurements and analysis to be performed on cameras. LI, medical physicist from the department of nuclear medicine at CHRU Nancy, welcomed CH and LF and all participated in VERITON measurements. GLR, medical physicist from the department of nuclear medicine at CHU Orléans, welcomed CH and PMK and all participated in StarGuide measurements. CH performed the analysis (spectra and reconstructed images). CH, PMK and LF wrote a first version of the manuscript. They participated in meetings with vendors to discuss the results and to validate the Discussion section. All authors reviewed the draft version until final validation.

## Declarations

### Competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Received: 6 February 2024 Accepted: 16 September 2024

Published online: 24 October 2024

## References

1. Ritt P. Recent developments in SPECT/CT. Semin Nucl Med. 2022;52(3):276-85. https://doi.org/10.1053/j semnu clmed.2022.01.004. (Epub 2022 Feb 21 PMID: 35210065).

2. Imbert L, Marie PY. CZT cameras: a technological jump for myocardial perfusion SPECT. J Nucl Cardiol. 2016;23(4):894-6. https://doi.org/10.1007/s12350-015-0216-2. (Epub 2015 Jun 25 PMID: 26108415).

3. Fernandez P. Retour d'expérience: installation et utilisation de la Discovery NM/CT 670 CZT. Médecine Nucléaire. 2019;43(2):241-3. https://doi.org/10.1016/j.mednuc.2019.01.038.

4. Koulikov V, Lerman H, Kesler M, Even-Sapir E. (99m)Tc-MDP bone scintigraphy of the hand: comparing the use of novel cadmium zinc telluride (CZT) and routine NaI(Tl) detectors. EJNMMI Res. 2015;5(1):63. https://doi.org/10.1186/s13550-015-0139-6.

5. Keider Z, Raysberg I, Lugassi R, Frenkel A, Israel O. Novelcadmium zinc telluride based detector general purpose gammacamera: initial evaluation and comparison with a standard camera. J Nucl Med. 2016;57(Suppl 2):S259.

6. Goshen E, Beilin L, Stern E, Kenig T, Goldkorn R, Ben-Haim S. Feasibility study of a novel general purpose CZT-based digital SPECT camera: initial clinical results. EJNMMI Phys. 2018;5(1):6. https://doi.org/10.1186/s40658-018-0205-z.

7. Desmonts C, Bouthiba MA, Enilorac B, Nganoa C, Agostini D, Aide N. Evaluation of a new multipurpose whole-body CzT-based camera: comparison with a dual-head Anger camera and first clinical images. EJNMMI Phys. 2020;7(1):18. https://doi.org/10.1186/s40658-020-0284-5.

8. Serrano B, Amblard R, Beaumont T, Hugonnet F, Dietz M, Berthier F, Garnier N, Villeneuve R, Nataf V, Mocquot F, Montemagno C, Faraggi M, Paulmier B. Quantitative analysis of 99mTc-pertechnetate thyroid uptake with a
large-field CZT gamma camera: feasibility and comparison between SPECT/CT and planar acquisitions. EJNMMI Phys. 2023;10(1):45. https://doi.org/10.1186/s40658-023-00566-3.

9. Ito T, Matsusaka Y, Onoguchi M, Ichikawa H, Okuda K, Shibutani T, Shishido M, Sato K. Experimental evaluation of the GE NM/CT 870 CZT clinical SPECT system equipped with WEHR and MEHRS collimator. J Appl Clin Med Phys. 2021;22(2):165-77. https://doi.org/10.1002/acm2.13158.

10. Le Rouzic G, Zananiri R. First performance measurements of a new multi-detector CZT-Based SPECT/CT system: GE StarGuide. J Nucl Med. 2021;62(Suppl 1):S1125.

11. SYSTEM SPECIFICATIONS VERITON-CT Series 360° CZT Digital SPECT/CT MAR0035 Rev C | September 2023. https://www.cccurie.be/wp-content/uploads/2023/09/SpecSheet_VERITON-CT_MAR0035-Rev-A_Feb-2023v10-1.pdf

12. Ichikawa H, Shibutani T, Matsutake Y, Kato T, Ikematsu R, Higashi R, Kamiya T, Shimada H, Onoguchi M. Comparison of the detectability of hot lesions on bone SPECT using six state-of-the-art SPECT/CT systems: a multicenter phantom study to optimize reconstruction parameters. Phys Eng Sci Med. 2023;46(2):839-49. https://doi.org/10.1007/s13246-023-01257-0. (Epub 2023 May 1 PMID: 37126151).

13. Carsuzza T, Thibault F, Bailly M. Gated tomographic radionuclide angiography using 3D-ring CZT StarGuide SPECT/CT head-to-head comparison with a cardiac-dedicated CZT camera: first clinical use and validation. Clin Nucl Med. 2022;47(7):e515-7. https://doi.org/10.1097/RLU.0000000000004153. (Epub 2022 Mar 31 PMID: 35353756).

14. Callaud A, Metrard G, Bailly M. 3D-ring CZT system with new low- and medium-energy range: ultrafast dual-isotope lung SPECT/CT improvement. Clin Nucl Med. 2023;48(8):716-8. https://doi.org/10.1097/RLU.0000000000004706.

15. Besse H, Bailly M. Case report: potential applications of using a 3D-ring CZT SPECT for lymphoscintigraphic exploration of lower limb edema. Front Med (Lausanne). 2022;22(9):866541. https://doi.org/10.3389/fmed.2022.866541.

16. Bailly M, Le Rouzic G, Metrard G. Ultra-fast high resolution whole-body SPECT after treatment with 153Sm-EDTMP using 3D-ring CZT: applying new technology to an old tracer. Eur J Nucl Med Mol Imaging. 2023;50(3):968-9. https://doi.org/10.1007/s00259-022-06029-8. (Epub 2022 Nov 7 PMID: 36342522).

17. Cerić Andelius I, Minaric D, Persson E, Mosén H, Valind K, Trägårdh E, Oddstig J. First clinical experience of a ring-configured cadmium zinc telluride camera: A comparative study versus conventional gamma camera systems. Clin Physiol Funct Imaging. 2023. https://doi.org/10.1111/cpf.12853.

18. Song H, Ferri Y, Duan H, Aparici CM, Davidzon G, Franc BL, Moradi F, Nguyen J, Shah J, Iagaru A. SPECT at the speed of PET: a feasibility study of CZT-based whole-body SPECT/CT in the post 177Lu-DOTATATE and 177Lu-PSMA617 setting. Eur J Nucl Med Mol Imaging. 2023;50(8):2250-7. https://doi.org/10.1007/s00259-023-06176-6. (Epub 2023 Mar 4 PMID: 36869177).

19. Komber H, Little D, Cade S, Graham R, Redman S. Comparing the patient experience between a novel 360° gamma camera (VERITON-CT) and a conventional dual head gamma camera. J Nucl Med Technol. 2021;50(2):132-6. https://doi.org/10.2967/jnmt.121.262627.

20. Peters SMB, van der Werf NR, Segbers M, van Velden FHP, Wierts R, Blokland KJAK, Konijnenberg MW, Lazarenko SV, Visser EP, Gotthardt M. Towards standardization of absolute SPECT/CT quantification: a multi-center and multi-vendor phantom study. EJNMMI Phys. 2019;6(1):29. https://doi.org/10.1186/s40658-019-0268-5.

21. Peters SMB, Meyer Viol SL, van der Werf NR, de Jong N, van Velden FHP, Meeuwis A, Konijnenberg MW, Gotthardt M, de Jong HWAM, Segbers M. Variability in lutetium-177 SPECT quantification between different state-of-the-art SPECT/CT systems. EJNMMI Phys. 2020;7(1):9. https://doi.org/10.1186/s40658-020-0278-3.

22. Danieli R, Stella M, Leube J, Tran-Gia J, Marin C, Uribe CF, Vanderlinden B, Reynaert N, Flamen P, Levillain H. Quantitative 177Lu SPECT/CT imaging for personalized dosimetry using a ring-shaped CZT-based camera. EJNMMI Phys. 2023;10(1):64. https://doi.org/10.1186/s40658-023-00586-z.

23. Vergnaud L, Badel JN, Giraudet AL, Kryza D, Mognetti T, Baudier T, Rida H, Dieudonné A, Sarrut D. Performance study of a 360° CZT camera for monitoring 177Lu-PSMA treatment. EJNMMI Phys. 2023;10(1):58. https://doi.org/10.1186/s40658-023-00576-1.

24. Nuttens V, Schramm G, D'Asseler Y, Koole M. Comparison of a 3D CZT and conventional SPECT/CT system for quantitative Lu-177 SPECT imaging. EJNMMI Phys. 2024;11(1):29. https://doi.org/10.1186/s40658-024-00627-1.

25. Greffier J, Barbotteau Y, Gardavaud F. iQMetrix-CT: new software for task-based image quality assessment of phantom CT images. Diagn Interv Imaging. 2022;103(11):555-62. https://doi.org/10.1016/j.diii.2022.05.007. (Epub 2022 Jul 2 PMID: 35792006).

26. Report No. 233 - Performance Evaluation of Computed Tomography Systems - The Report of AAPM Task Group 233 (2019).

27. O. Couturier. SFMN. Enquête nationale. SFMN (2020)

28. Langbein T, Weber WA, Eiber M. Future of theranostics: an outlook on precision oncology in nuclear medicine. J Nucl Med. 2019;60(Suppl 2):13S-19S. https://doi.org/10.2967/jnumed.118.220566. (PMID: 31481583).

29. Mezzenga E, D'Errico V, D'Arienzo M, Strigari L, Panagiota K, Matteucci F, Severi S, Paganelli G, Fenwick A, Bianchini D, Marcocci F, Sarnelli A. Quantitative accuracy of 177Lu SPECT imaging for molecular radiotherapy. PLoS One. 2017;12(8):e0182888. https://doi.org/10.1371/journal.pone.0182888.

30. Thuillier P, Maajem M, Schick U, Blanc-Beguin F, Hennebicq S, Metges JP, Salaun PY, Kerlan V, Bourhis D, Abgral R. Clinical assessment of 177Lu-DOTATATE quantification by comparison of SUV-based parameters measured on both post-PRRT SPECT/CT and 68Ga-DOTATOC PET/CT in patients with neuroendocrine tumors: a feasibility study. Clin Nucl Med. 2021;46(2):111-8. https://doi.org/10.1097/RLU.0000000000003412. (PMID: 33234927).

31. Morland D, Triumbari EKA, Hoog C, Sézin G, Dejust S, Cadiot G, Paris P, Papathanassiou D. Predicting subacute hematological toxicity of 177Lu-DOTATATE therapy using healthy organs' uptake on post-treatment quantitative SPECT: a pilot study. Medicine (Baltimore). 2022;101(49):e32212. https://doi.org/10.1097/MD.00000000000032212.

32. Vergnaud L, Dewaraja YK, Giraudet AL, et al. A review of 177Lu dosimetry workflows: how to reduce the imaging workloads? EJNMMI Phys. 2024;11:65. https://doi.org/10.1186/s40658-024-00658-8.

33. Carter LM, Ocampo Ramos JC, Kesner AL. Personalized dosimetry of 177Lu-DOTATATE: a comparison of organ- and voxel-level approaches using open-access images. Biomed Phys Eng Express. 2021. https://doi.org/10.1088/2057-1976/ac1550.10.1088/2057-1976/ac1550.
34. Violet J, Jackson P, Ferdinandus J, Sandhu S, Akhurst T, Iravani A, Kong G, Kumar AR, Thang SP, Eu P, Scalzo M, Murphy D, Williams S, Hicks RJ, Hofman MS. Dosimetry of 177Lu-PSMA-617 in metastatic castration-resistant prostate cancer: correlations between pretherapeutic imaging and whole-body tumor dosimetry with treatment outcomes. J Nucl Med. 2019;60(4):517-23. https://doi.org/10.2967/jnumed.118.219352. (Epub 2018 Oct 5 PMID: 30291192).

35. Miwa K, Yoshi T, Wagatsuma K, Nezu S, Kamitaka Y, Yamao T, Kobayashi R, Fukuda S, Yakushiji Y, Miyaji N, Ishii K. Impact of y factor in the penalty function of Bayesian penalized likelihood reconstruction (Q.Clear) to achieve high-resolution PET images. EJNMMI Phys. 2023;10(1):4. https://doi.org/10.1186/s40658-023-00527-w.

36. Nelson JS, Christianson OI, Harkness BA, Madsen MT, Mah E, Thomas SR, et al. Improved nuclear medicine uniformity assessment with noise texture analysis. J Nucl Med. 2014;55(1):169-74.

37. Hoog C, Verrecchia-Ramos E, Dejust S, Lalire P, Sezin G, Moubtakir A, El Farsaoui K, Caquot PA, Guendouzen S, Morland D, Papathanassiou D. Implementation of xSPECT, xSPECT bone and Broadquant from literature, clinical survey and innovative phantom study with task-based image quality assessment. Phys Med. 2023;112:102611. https://doi.org/10.1016/j.ejmp.2023.102611. (Epub 2023 Jun 15 PMID: 37329742).

38. Bailey DL, Willowson KP, Muñoz-Ferrada C. A practical method for assessing quantitative scanner accuracy with long-lived radionuclides: the ARTnet insert. Asia Ocean J Nucl Med Biol. 2024;12(1):27-34. https://doi.org/10.22038/AOJNMB.2023.71860.1503.

39. Tran-Gia J, Denis-Bacelar AM, Ferreira KM, Robinson AP, Calvert N, Fenwick AJ, Finocchiaro D, Fioroni F, Grassi E, Heertun W, Jewitt SJ, Kotzassarlidou M, Ljungberg M, McGowan DR, Scott N, Scuffham J, Gleisner KS, Tipping J, Wevrett J, MRTDosimetry Collaboration, Lassmann M. A multicentre and multi-national evaluation of the accuracy of quantitative Lu-177 SPECT/CT imaging performed within the MRTDosimetry project. EJNMMI Phys. 2021;8(1):55. https://doi.org/10.1186/s40658-021-00397-0.

40. Report No. 177 - Acceptance Testing and Annual Physics Survey Recommendations for Gamma Camera, SPECT, and SPECT/CT Systems (2019)

41. Sjogreen Gleisner K, Chouin N, Gabina PM, Cicone F, Gnesin S, Stokke C, et al. EANM dosimetry committee recommendations for dosimetry of 177Lu-labelled somatostatin-receptor- and PSMA-targeting ligands. Eur J Nucl Med Mol Imaging. 2022;49(6):1778-809. https://doi.org/10.1007/s00259-022-05727-7.

42. Bordonne M, Chawki MB, Marie PY, Zaragori T, Roch V, Grignon R, Imbert L, Verger A. High-quality brain perfusion SPECT images may be achieved with a high-speed recording using 360° CZT camera. EJNMMI Phys. 2020;7(1):65. https://doi.org/10.1186/s40658-020-00334-7.

43. Bahloul A, Verger A, Blum A, Chawki M, Perrin M, Melki S, Karcher G, Marie P, Imbert L. Bone scintigraphy of vertebral fractures with a whole-body CZT camera in a PET-like utilization. Front Nucl Med. 2021. https://doi.org/10.3389/fnume.2021.740275.

44. Sézin G, Lalire P, Hoog C, Moubtakir A, Dejust S, El Farsaoui K, Morland D, Papathanassiou D. Évaluation de la modalité de reconstruction xSPECT bone dans la détection de lésions osseuses secondaires en scintigraphie osseuse. Méd Nucl. 2024. https://doi.org/10.1016/j.mednuc.2023.09.009.

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