[Evaluation of Measurement Accuracy and Inter-institutional Comparison for Dose Calibrators].

PURPOSE: The aim of this study was to validate the reliability of dose calibrators for measuring the radioactivity of several radioisotopes in multi-institution. METHODS: We evaluated the measurement accuracy of dose calibrators using a commercially available source ((67) Ga, (99m) Tc, (123) I, (201) TL). Nine dose calibrators (five models) in seven institutions were performed in this study. Each source was measured at least 3 times a day over a period of 4 half-life. Linearity of concentration (%error value) and percent difference values (%diff measurement) between measured and estimated radioactivity were calculated to evaluate the measurement accuracy. In addition, difference among institutions (%diff institution) was evaluated by the error values between measured and reference institution values. RESULTS: Good linearity of concentration was found between measured and estimated radioactivity in (99m)Tc and (123)I. However, %error value was increased in (67)Ga and (201)TL (maximum 19.3%). %diff measurements were 1.9 ± 0.3% for (67)Ga, -0.9 ± 0.3% for (99m)Tc, 2.2 ± 0.4% for (123)I, and -0.7 ± 0.3% for (201)TL, respectively. Although there were no clear differences in six institutions, %diff institution in one institution tended to be higher than that obtained in other institutions. CONCLUSIONS: Our results indicated that measurement accuracy of nine dose calibrators (five models) was relatively stable. However, difference of measured values tended to be higher in a part of institution and source. It is important to perform quality assurance and quality control for dose calibrator using traceable source.

Evaluation of Resolution Recovery for Each Collimator in Brain Perfusion Image.

PURPOSE: This study aimed to verify the resolution recovery for each collimator in the brain perfusion image. METHOD: To verify the effect of the resolution recovery for each collimator, we evaluated via the three-dimensional brain phantom (phantom) and the normal brain perfusion single photon emission computed tomography (SPECT) data. These data were reconstructed using the three-dimensional ordered subset expectation maximization method (3D-OSEM) (Evolution for boneTM) that was performed with scatter correction, attenuation correction, and resolution recovery (RR). The performance of resolution recovery was evaluated in the two collimator systems (ELEGP and MEGP) reconstruction condition via the contrast value, mean counts, normalized mean square error (NMSE), and regional brain activity. RESULT: In the "with resolution recovery (+RR)", the NMSE indicated minimum value with SI (subset×iteration) = 100, cut-off frequency (Fc) = 0.50 cycles/cm. The contrast value in the "+RR" increased 20% for the cortical region and decreased 28% and 6% at ELEGP collimator and MEGP collimator for the central region, as compared to the "without resolution recovery (-RR)". In the phantom study, the error of the brain activity using MEGP collimator at the temporal lobe and sub-lobar decreased 15%, compared with ELEGP collimator in the + RR. In the clinical study, the error of the regional brain activity using MEGP collimator in the "+RR" increased from 3% to 8%, compared with "-RR". DISCUSSION: The accurate resolution recovery was obtained at SI = 100 and Fc = 0.50 cycles/cm. The contrast value and regional brain activity at the central region decreased due to incomplete resolution recovery by use of ELEGP collimator.

[Influence of a radioisotope from out of the effective field of view in a semiconductor single photon emission computed tomography scanner].

Discovery NM 530c (CZT SPECT) is a new single photon emission computed tomography (SPECT) scanner using a cadmium-zinc-telluride (CZT) solid-state semiconductor detector technology. Due to multi-pinhole collimator design of this system, each CZT detector facing different direction and be able to get incidence radioactivity from radioisotopes (RIs) existing outside of effective field of view (EFOV). The purpose of this study is to verify its impact and compare it to a conventional Anger-type SPECT scanner (Discovery NM/CT 670 pro). We used (99m)TcO4(-) as radiation source and set it outside of the EFOV at several different positions (height and angle) and scanned by both the cameras. As a result, CZT SPECT got more influence compared to Anger-type SPECT. The impact was different according to its height. When using other RIs in CZT SPECT room, it is important to confirm the appropriate position against CZT SPECT during scan.

[Comparison of Quantitative Value of Dopamine Transporter Scintigraphy Calculated from Different Analytical Software].

In the dopamine transporter scintigraphy there are two quantitative analysis softwares, DaTView and DaTQUANT. The quantitative value of both software has to be treated independently because there is a difference between them in the point of how to set the region of interest on the striatum and the background, calculation formula of quantitation. And also DaTQUANT has a capability of performing anatomical standardization which DaTView does not have. The aim of this study was to evaluate the accuracy of registration on DaTQUANT using a phantom, and to evaluate the correlation between the quantitative values between DaTView and DaTQUANT using clinical data. As a result, the accuracy of registration was acceptable. Regardless of the degree of accumulation in the striatum, there was a high correlation to each analysis software (r>0.85).

Administered dosage and effective dose estimated from 81Rb-rubidium hydroxide for lung ventilation scintigraphy using 81mKr noble gas.

The aim of this study was to estimate the administered dosage of 81mKr noble gas as calculated by the radioactivity of 81Rb-rubidium hydroxide (81RbOH). The administered dosage was regarded as the total amount of 81mKr noble gas. The radioactivity of 81mKr was calculated using the radioactivity of 81RbOH at the examination, the beginning of inhalation, the inhalation duration and the attenuation volume from the generator to the patient for 81mKr noble gas. In addition, we created an Internet survey and asked National University Hospital in Japan to respond to questions regarding the parameters of concern. Survey responses were provided by 38 hospitals (response rate was 90.5%). Twenty-seven hospitals (64.3%) examined lung ventilation scintigraphy using 81mKr noble gas. The mean administered dosage and the effective dose of lung ventilation scintigraphy using 81mKr noble gas were 35.8 ± 22.1 GBq and 0.97 ± 0.60 mSv, respectively.

Exploration of tumor size measurement methods in preoperative breast cancer assessment using whole-body silicon photomultiplier PET: feasibility and first results.

PURPOSE: Whole-body silicon photomultiplier positron emission tomography (WB SiPM PET) could be used to diagnose breast cancer spread before lumpectomy. We aimed to investigate the method of measuring the tumor size by WB SiPM PET as a basis for diagnosing breast cancer spread in the breast. MATERIALS AND METHODS: We retrospectively reviewed 35 breast cancer lesions in 32 patients who underwent WB SiPM PET/CT in the prone position as preoperative breast cancer examinations from September 2020 to March 2022. In all cases, a 20-mm spherical VOI was placed in the normal mammary gland to measure the mean standardised uptake value (SUVmean) and the standard deviation (SD) of 18F-fluorodeoxyglucose (FDG) uptake. We prepared four types of candidates (SUVmean + 2 SD, SUVmean + 3 SD, 1.5 SUVmean + 2 SD, 1.5 SUVmean + 3 SD) for thresholds for delineating tumor contours on PET images. On the semiautomatic viewer soft, the maximum tumor sizes were measured at each of the four thresholds and compared with the pathological tumor sizes, including the extensive intraductal component (EIC). RESULTS: The lesion detection sensitivity was 97% for WB SiPM PET. PET detected 34 lesions, excluding 4-mm ductal carcinomas in situ (DCIS). PET measurements at the '1.5 SUVmean + 2 SD' threshold demonstrated values closest to the pathological tumor sizes, including EIC. Moreover, '1.5 SUVmean + 2 SD' had the highest concordance (63%). CONCLUSIONS: The study demonstrated that among various PET thresholds, the '1.5 SUVmean + 2 SD' threshold exhibited the best performance. However, even with this threshold, the concordance rate was limited to only 63%.

[Accuracy of Classification of Cerebral Blood Flow Reduction Patterns Using Statistical Analysis Images Generated with Simulated SPECT Datasets via Deep Learning].

PURPOSE: The aim of this study was to evaluate the classification accuracy of specific blood flow reduction patterns in clinical images by deep learning using simulation data. METHODS: We obtained Z-score maps for 100 cases each of simulated Alzheimer's disease (AD), simulated dementia with Lewy bodies (DLB), and simulated normal cognition (NC) by performing statistical analysis of the simulation data that provided defects and healthy patient data. The clinical images were determined by reference to radiological reports, and Z-score maps of AD (n=33), DLB (n=20), and NC (n=28) were used. A network was constructed with reference to AlexNet, 4-fold cross-validation was performed using only simulation data, and classification accuracy was evaluated. We also trained the model using the simulation data and classified the clinical images. RESULTS: The accuracy rate of classification between simulations was 96.2% and that of the clinical images was 84.2%. CONCLUSION: Through deep learning using simulation data, clinical images may be classified with an accuracy of 84.2%.

[Examination of axial zygomatic arch radiographs using the bisector method].

An axial radiograph of the zygomatic arch is taken in cases of patients with facial traumatic injury. Maintaining the patient's head in the retroflex position to take such axial radiographs is sometimes difficult because of medical conditions. In addition, since different positioning techniques for retroflexion are used by radiological technologists, the visibility of the zygomatic arch was poorly in reproduced. We contrived a novel technique for use in taking a zygomatic arch radiograph. We call it the "bisector method," and it does not require the retroflex position. We can take a zygomatic arch radiograph equal in quality to conventional axial radiographs (retroflex position) by exposing X-rays perpendicularly to the bisector of the angle between the casette and the zygomatic arch. This bisector method is relatively easy in that it does not require either the retroflex position or the expertise of a radiological technologist.

Impact of quantitative index derived from 123I-FP-CIT-SPECT on reconstruction with correction methods evaluated using a 3D-striatum digital brain phantom.

We evaluated quantitation accuracy of the specific binding ratio (SBR) and specific uptake ratio (SUR) of dopamine transporter for various correction methods by using a novel three-dimensional striatum digital brain (3D-SDB) phantom comprised of segments containing the striatum, ventricle, brain parenchyma, and skull bone extracted from T2-weighted MR images. A process image was reconstructed by projection data sets with blurring, scatter, and attenuation from 3D-SDB phantom data. A 3D-iterative reconstruction algorithm was used without correction (OSEM), or with scatter (SC), attenuation (AC), AC + SC (ACSC), AC + resolution recovery (RR; ACRR), SC + RR (SCRR), AC + SC + RR (ACSCRR), AC + SC + RR + partial volume (PVC; ACSCRRP), and AC + SC + RR + PVC + ventricle (ACSCRRPV). Data were then quantified using SBR and SUR. Differences between measured and true SBR values were (in order): ACSCRR < ACSC < ACRR < AC < SCRR < SC < OSEM: the maximal error was 45.3%. The trend of differences between measured and true SUR values was similar to that of SBR; maximal error was 65%. The ACSCRR-corrected SUR, which was closer to the true value, was underestimated by 30.4%. However, the ACSCRRP-corrected SUR was underestimated by a maximum of 22.5%. The SUR in the ACSCRRPV was underestimated by 6.2%. The accuracy of quantitation was improved using various types of compensation and correction. Accuracy improved more for the SUR when PVC and ventricle correction were added.

Can a Resting-State Functional Connectivity Index Identify Patients with Alzheimer's Disease and Mild Cognitive Impairment Across Multiple Sites?

Resting-state functional connectivity is one promising biomarker for Alzheimer's disease (AD) and mild cognitive impairment (MCI). However, it is still not known how accurately network analysis identifies AD and MCI across multiple sites. In this study, we examined whether resting-state functional connectivity data from the Alzheimer's Disease Neuroimaging Initiative (ADNI) could identify patients with AD and MCI at our site. We implemented an index based on the functional connectivity frequency distribution and compared performance for AD and MCI identification with multivoxel pattern analysis. The multivoxel pattern analysis using a connectivity map of the default mode network showed good performance, with an accuracy of 81.9% for AD and MCI identification within the ADNI, but the classification model obtained from the ADNI failed to classify AD, MCI, and healthy elderly adults from our site, with an accuracy of only 43.1%. In contrast, a functional connectivity index of the medial temporal lobe based on the frequency distribution showed moderate performance, with an accuracy of 76.5-80.3% for AD identification within the ADNI. The performance of this index was similar for our data, with an accuracy of 73.9-82.6%. The frequency distribution-based index of functional connectivity could be a good biomarker for AD across multiple sites.

Effect of resolution recovery using graph plots on regional cerebral blood flow in healthy volunteers.

PURPOSE: We evaluated the effect of resolution recovery (RR) using graph plots on regional cerebral blood flow (rCBF) in brain perfusion single-photon emission computed tomography (SPECT) images derived from healthy volunteers and patients diagnosed with probable Alzheimer's disease. METHOD: We acquired brain perfusion SPECT images with scatter correction (SC), computed tomography-based attenuation correction (CTAC), and RR from a three-dimensional brain phantom and from healthy volunteers. We then compared contrast-to-noise ratio, count density ratios, increase maps, and rCBF using statistical parametric mapping 8. RESULTS: Regional brain counts were significantly increased from 20-24% with SC, CTAC, and RR compared with SC and CTAC. Mean CBF in healthy volunteers was 42.5 ± 5.4 mL/100 g/min. Average rCBF determined using SC, CTAC and RR increased 7.5, 2.0, and 3.7% at the thalamus, posterior cingulate, and whole brain, respectively, compared with SC and CTAC. CONCLUSION: Resolution recovery caused variations in normal rCBF because counts increased in cerebral regions.

Use of a digital phantom developed by QIBA for harmonizing SUVs obtained from the state-of-the-art SPECT/CT systems: a multicenter study.

BACKGROUND: Although quantitative analysis using standardized uptake value (SUV) becomes realistic in clinical single-photon emission computed tomography/computed tomography (SPECT/CT) imaging, reconstruction parameter settings can deliver different quantitative results among different SPECT/CT systems. This study aims to propose a use of the digital reference object (DRO), which is a National Electrical Manufacturers Association (NEMA) phantom-like object developed by the Quantitative Imaging Biomarker Alliance (QIBA) fluorodeoxyglucose-positron emission tomography technical committee, for the purpose of harmonizing SUVs in Tc-99m SPECT/CT imaging. METHODS: The NEMA body phantom with determined Tc-99m concentration was scanned with the four state-of-the-art SPECT/CT systems. SPECT data were reconstructed using different numbers of the product of subset and iteration numbers (SI) and the width of 3D Gaussian filter (3DGF). The mean (SUVmean), maximal (SUVmax), and peak (SUVpeak) SUVs for six hot spheres (10, 13, 17, 22, 28, and 37 mm) were measured after converting SPECT count into SUV using Becquerel calibration factor. DRO smoothed by 3DGF with a FWHM of 17 mm (DRO17 mm) was generated, and the corresponding SUVs were measured. The reconstruction condition to yield the lowest root mean square error (RMSE) of SUVmeans for all the spheres between DRO17 mm and actual phantom images was determined as the harmonized condition for each SPECT/CT scanner. Then, inter-scanner variability in all quantitative metrics was measured before (i.e., according to the manufacturers' recommendation or the policies of their own departments) and after harmonization. RESULTS: RMSE was lowest in the following reconstruction conditions: SI of 100 and 3DGF of 13 mm for Brightview XCT, SI of 160 and 3DGF of 3 pixels for Discovery NM/CT, SI of 60 and 3DGF of 2 pixels for Infinia, and SI of 140 and 3DGF of 15 mm for Symbia. In pre-harmonized conditions, coefficient of variations (COVs) among the SPECT/CT systems were greater than 10% for all quantitative metrics in three of the spheres, SUVmax and SUVmean, in one of the spheres. In contrast, all metrics except SUVmax in the 17-mm sphere yielded less than 10% of COVs after harmonization. CONCLUSIONS: Our proposed method clearly reduced inter-scanner variability in SUVs. A digital phantom developed by QIBA would be useful for harmonizing SUVs in multicenter trials using SPECT/CT.

Does applying resolution recovery to normal databases confer an advantage over conventional 3D-stereotactic surface projection techniques?

We evaluated a novel normal database (NDB) generated using single photon emission computed tomography (SPECT) data obtained from healthy brains by using a SPECT/CT system, analyzed using a resolution recovery (RR) technique applied to the three-dimensional stereotactic surface projection (3D-SSP) technique. We used a three-dimensional ordered subset expectation maximization method (3D-OSEM) with applied scatter correction (SC), attenuation correction, and RR to reconstruct the data. We verified the accuracy of the novel NDB's values (Z, extent, and error scores), and compared the novel NDB to the 3D-SSP technique by using simulated misery perfusion-related patient data from a conventional NDB. In addition, Z, extent, and error scores at the precuneus, cuneus, and posterior cingulate were compared under different reconstruction conditions by using the patient data. In the simulation, Z scores decreased when using the novel NDB corrected using computed tomography-based attenuation correction (CTAC), SC, and RR. The extent scores of the posterior cingulate increased using the novel NDB, relative to the other NDBs. The error score with the novel NDB without RR decreased by 15% compared to that of the conventional NDB. Z scores generated from patient data decreased in the novel NDB with RR. The extent scores tended to decrease in the novel NDB with RR. The extent scores in the novel NDB with RR improved at the posterior cingulate, compared to the scores with the other NDBs. However, applying RR to the novel NDB conferred no advantage because the cut-off of the current Z score must be reconsidered when using the additive RR technique.

Validation of Computed Tomography-based Attenuation Correction of Deviation between Theoretical and Actual Values in Four Computed Tomography Scanners.

OBJECTIVES: In this study, we aimed to validate the accuracy of computed tomography-based attenuation correction (CTAC), using the bilinear scaling method. METHODS: The measured attenuation coefficient (µm) was compared to the theoretical attenuation coefficient (µt), using four different CT scanners and an RMI 467 phantom. The effective energy of CT beam X-rays was calculated, using the aluminum half-value layer method and was used in conjunction with an attenuation coefficient map to convert the CT numbers to µm values for the photon energy of 140 keV. We measured the CT number of RMI 467 phantom for each of the four scanners and compared the µm and µt values for the effective energies of CT beam X-rays, effective atomic numbers, and physical densities. RESULTS: The µm values for CT beam X-rays with low effective energies decreased in high construction elements, compared with CT beam X-rays of high effective energies. As the physical density increased, the µm values elevated linearly. Compared with other scanners, the µm values obtained from the scanner with CT beam X-rays of maximal effective energy increased once the effective atomic number exceeded 10.00. The µm value of soft tissue was equivalent to the µt value. However, the ratios of maximal difference between µm and µt values were 25.4% (lung tissue) and 21.5% (bone tissue), respectively. Additionally, the maximal difference in µm values was 6.0% in the bone tissue for each scanner. CONCLUSION: The bilinear scaling method could accurately convert CT numbers to µ values in soft tissues.