Noriaki Miyaji

Evaluation of a revised version of computer-assisted diagnosis system, BONENAVI version 2.1.7, for bone scintigraphy in cancer patients

ObjectiveBONENAVI is a computer-assisted diagnosis system that analyzes bone scintigraphy automatically. We experienced more than a few segmentation errors with the previous BONENAVI version (2.0.5). We have since obtained a revised version (2.1.7) and evaluate it.MethodsBone scans of patients were analyzed by BONENAVI version 2.0.5 and a revised version 2.1.7 with regard to segmentation errors, sensitivity, and specificity. Patients with skeletal metastases from prostate cancer, lung cancer, breast cancer, and other cancers were included in the study as true-positive cases. Patients with no skeletal metastasis (regardless of hot spots), and patients with abnormal bone scans but no skeletal metastasis were included as negative cases. Bone-scan patients were subjected to artificial neural network (ANN) evaluation. Values equal to or above 0.5 were regarded as positive, and those below 0.5 as negative. The patients whose clinical status did not correspond to their ANN scores were assessed for any similarities.ResultsThe frequency of segmentation errors was statistically significantly reduced when using BONENAVI version 2.1.7. The differences in sensitivity and specificity for the results of version 2.0.5 versus version 2.1.7 were not different, giving a high Cohen’s kappa coefficient. In the patients who showed an increased ANN value with version 2.1.7, a few false-positive thoracic lesions were identified. Patients whose ANN value was significantly high with version 2.0.5 showed no tendencies.ConclusionRevised BONENAVI version 2.1.7 for bone scintigraphy was superior with regard to segmentation errors. However, its sensitivity and specificity were similar to those of version 2.0.5. The false-positive identification of thoracic lesions in revised version 2.1.7 might be subject to remedy.

Evaluation of scatter limitation correction: a new method of correcting photopenic artifacts caused by patient motion during whole-body PET/CT imaging.

ObjectiveOvercorrection of scatter caused by patient motion during whole-body PET/computed tomography (CT) imaging can induce the appearance of photopenic artifacts in the PET images. The present study aimed to quantify the accuracy of scatter limitation correction (SLC) for eliminating photopenic artifacts. MethodsThis study analyzed photopenic artifacts in 18F-fluorodeoxyglucose (18F-FDG) PET/CT images acquired from 12 patients and from a National Electrical Manufacturers Association phantom with two peripheral plastic bottles that simulated the human body and arms, respectively. The phantom comprised a sphere (diameter, 10 or 37 mm) containing fluorine-18 solutions with target-to-background ratios of 2, 4, and 8. The plastic bottles were moved 10 cm posteriorly between CT and PET acquisitions. All PET data were reconstructed using model-based scatter correction (SC), no scatter correction (NSC), and SLC, and the presence or absence of artifacts on the PET images was visually evaluated. The SC and SLC images were also semiquantitatively evaluated using standardized uptake values (SUVs). ResultsPhotopenic artifacts were not recognizable in any NSC and SLC image from all 12 patients in the clinical study. The SUVmax of mismatched SLC PET/CT images were almost equal to those of matched SC and SLC PET/CT images. Applying NSC and SLC substantially eliminated the photopenic artifacts on SC PET images in the phantom study. SLC improved the activity concentration of the sphere for all target-to-background ratios. The highest %errors of the 10 and 37-mm spheres were 93.3 and 58.3%, respectively, for mismatched SC, and 73.2 and 22.0%, respectively, for mismatched SLC. ConclusionPhotopenic artifacts caused by SC error induced by CT and PET image misalignment were corrected using SLC, indicating that this method is useful and practical for clinical qualitative and quantitative PET/CT assessment.

Evaluation of bone metastatic burden by bone SPECT/CT in metastatic prostate cancer patients: defining threshold value for total bone uptake and assessment in radium-223 treated patients

ObjectivesTo establish a new three-dimensional quantitative evaluation method for bone metastasis, we applied bone single photon emission tomography with computed tomography (SPECT/CT). The total bone uptake (TBU), which measures active bone metastatic burden, was calculated as the sum of [mean uptake obtained as standardized uptake value (SUV) above a cut-off level] × (the volume of the lesion) in the trunk using bone SPECT/CT. We studied the threshold value and utility of TBU in prostate cancer patients treated with radium-223 (Ra-223) therapy.MethodsTo establish the threshold value of TBU, we compared bone metastatic and non-metastatic regions in 61 prostate cancer patients with bone metastasis and 69 without. Five fixed sites in each patient were selected as evaluation points and divided into bone metastatic and non-metastatic sites. Sensitivity and specificity analysis was applied to establish the threshold level. Using the obtained threshold value, we then calculated the TBU in nine prostate cancer patients who received Ra-223 therapy, and compared the results with the bone scan index (BSI) by BONENAVI® and visual evaluation of bone scintigraphy.ResultsUptake was significantly lower in non-metastatic sites in patients with bone metastasis than in patients without metastasis. Sensitivity and specificity analysis revealed SUV = 7.0 as the threshold level. There was a discrepancy between TBU and BSI change in two of the nine patients, in whom TBU change correlated with visual judgement, but BSI change did not. In two patients, BSI was nearly 0 throughout the course, but the TBU was positive and changed, although the change was not large. These results suggest that TBU may be more accurate and sensitive than BSI for quantitative evaluation of active bone metastatic burden.ConclusionWe established a threshold value (SUV > 7.0) for three-dimensional TBU for evaluating active bone metastatic burden in prostate cancer patients using bone SPECT/CT. Despite the small number of patients, we expect the change in TBU could be more accurate and sensitive than the change in BSI among patients who received Ra-223.

Multicenter study of quantitative PET system harmonization using NIST-traceable 68Ge/68Ga cross-calibration kit

PURPOSE The present study aimed to define the errors in SUV and demonstrate the feasibility of SUV harmonization among contemporary PET/CT scanners using a novel National Institute of Standards and Technology (NIST)-traceable 68Ge/68Ga source as the reference standard. METHODS We used 68Ge/68Ga dose calibrator and PET sources made with same batch of 68Ge/68Ga embedded in epoxy that is traceable to the NIST standard. Bias in the amount of radioactivity and the radioactive concentrations measured by the dose calibrators and PET/CT scanners, respectively, was determined at five Japanese sites. We adjusted optimal dial setting of the dose calibrators and PET reconstruction parameters to close the actual amount of radioactivity and the radioactive concentration, respectively, of the NIST-traceable 68Ge/68Ga sources to harmonize SUV. Errors in SUV before and after harmonization were then calculated at each site. RESULTS The average bias in the amount of radioactivity and the radioactive concentrations measured by dose calibrator and PET scanner was -4.94% and -12.22%, respectively, before, and -0.14% and -4.81%, respectively, after harmonization. Corresponding averaged errors in SUV measured under clinical conditions were underestimated by 7.66%, but improved by -4.70% under optimal conditions. CONCLUSION Our proposed method using an NIST-traceable 68Ge/68Ga source identified bias in values obtained using dose calibrators and PET scanners, and reduced SUV variability to within 5% across different models of PET scanners at five sites. Our protocol using a standard source has considerable potential for harmonizing the SUV when contemporary PET scanners are involved in multicenter studies.

Comparison of 3 Devices for Automated Infusion of Positron-Emitting Radiotracers

The administration accuracy and precision of an automated infusion device for positron-emitting radiotracers are directly associated with bias and variance in the SUVs of 18F-FDG PET/CT. Therefore, the accuracy of such devices must be confirmed and calibrated at locations in which they are used. The present study aimed to validate the administration accuracy of 3 automated infusion devices for quantitative PET assessment. Methods: Temporal variations as well as variations in radioactive concentrations and dispensed volumes of 18F-FDG were determined for the M-130, AI-300, and UG-05 automated infusion devices. The total-test dispensed volumes were 25, 20, and 18.5 mL, respectively. A reference value was generated by measuring amounts of radioactivity using a standard dose calibrator. Administration accuracy was validated according to the criteria of the Japanese Society of Nuclear Medicine. Results: The temporal variation in the M-130 and UG-05 for a specified 185 MBq was relatively stable, in the range of −1.60%–0.92% and 1.16%–5.35%, respectively, whereas that in the AI-300 was −0.55%–8.68%. For the M-130 and UG-05 devices, the difference between measured and reference value was in the range of −5%–5%. The values measured by the AI-300 deviated from the reference values by a maximum of 30%, which depends on radioactive concentration and dispensed volume of 18F-FDG. Conclusion: The administration accuracy of the AI-300 varied considerably under different conditions, but a software update might somewhat improve this. Our findings indicate that dispensed volumes of 18F-FDG should be carefully considered when the radioactive concentration is high. Administration accuracy should be regularly confirmed at each location to maintain the quality of quantitative PET assessment. The present study provides useful information about how to confirm the administration accuracy of automated infusion devices.

Validation of Cross-calibration Schemes for Quantitative Bone SPECT/CT Using Different Sources under Various Geometric Conditions

PURPOSE Several cross-calibration schemes have been proposed to produce quantitative values in bone SPECT imaging. Differences in the radionuclide sources and geometric conditions can decrease the accuracy of cross-calibration factor (CCF). The present study aimed to validate the effects of calibration schemes using different sources under various geometric conditions. METHODS Temporal variations as well as variations in acquisition counts and the shapes of 57Co standard and 99mTc point sources and a 99mTc disk source were determined. The effects of the geometric conditions of the source-to-camera distance (SCD) and lateral distance on the CCF were investigated by moving the camera or source away from the origin. The system planar sensitivity of NEMA incorporated into a Symbia Intevo SPECT/CT device (Siemens®) was defined as reference values. RESULTS The temporal variation in CCF using the 57Co source was relatively stable within the range of 0.7% to 2.3%, whereas the 99mTc source ranged from 2.7% to 7.3%. In terms of source shape, the 57Co standard point source was the most stable. Both SCD and lateral distance decreased as a function of distance from the origin. Errors in the geometric condition were higher for the 57Co standard point source than the 99mTc disk source. CONCLUSIONS Different calibration schemes influenced the reliability of quantitative values. The 57Co standard point source was stable over a long period, and this helped to maintain the quality of quantitative SPECT/CT imaging data. The CCF accuracy of the 99mTc source decreased depending on the preparative method. The method of calibration for quantitative SPECT should be immediately standardized to eliminate uncertainty.

A Comparison of Planar Sensitivity and Spatial Resolution among Different Collimators and Energy Windows on 223 Ra Imaging

OBJECTIVE The present study aimed to reveal the influence of combination of different collimators and energy windows on the planar sensitivity and the spatial resolution during experimental 223Ra imaging, and to determine optimal imaging parameters. METHODS A vial type source containing 223Ra solution (4.55 MBq / 5.6 ml) was placed in the air at 100 mm away from the collimator surface. Planar images were acquired with LEHR, LMEGP, ELEGP and MEGP collimators on two dual-head gamma cameras (Symbia intevo (Siemens) and Infinia 3 (GE)). We compared three energy window combinations: 1) single window at 82 keV, 2) double window at 82+154 keV, 3) triple window at 82+154+270 keV. The energy spectrum, the sensitivity and the spatial resolution, such as full-width at half-maximum (FWHM) and full-width at tenth-maximum (FWTM), of each collimator were assessed. RESULTS Five energy spectra (at around 82, 154, 270, 351 and 405 keV) were essentially observed among four collimators. The sensitivity was high for LEHR collimator, then ELEGP and LMEGP collimator was 3-4 fold, which is greater than MEGP collimator. The 82 keV energy window of four collimators has best spatial resolution. Moreover, the spatial resolution of the 82 keV energy window with LMEGP and ELEGP collimator was almost equal to that of the triple window with MEGP collimator. CONCLUSIONS Optimal imaging parameters were single energy window using LMEGP or ELEGP, and then triple energy window using MEGP collimator.