Standardised uptake values from PET/CT images: comparison with conventional attenuation-corrected PET

Purpose In PET/CT, CT-derived attenuation factors may influence standardised uptake values (SUVs) in tumour lesions and organs when compared with stand-alone PET. Therefore, we compared PET/CT-derived SUVs intra-individually in various organs and tumour lesions with stand-alone PET-derived SUVs. Methods Thirty-five patients with known or suspected cancer were prospectively included. Sixteen patients underwent FDG PET using an ECAT HR+scanner, and subsequently a second scan using a Biograph Sensation 16PET/CT scanner. Nineteen patients were scanned in the reverse order. All images were reconstructed with an iterative algorithm (OSEM). Suspected lesions were grouped as paradiaphragmatic versus distant from the diaphragm. Mean and maximum SUVs were also calculated for brain, lung, liver, spleen and vertebral bone. The attenuation coefficients (μ values) used for correction of emission data (bone, soft tissue, lung) in the two data sets were determined. A body phantom containing six hot spheres and one cold cylinder was measured using the same protocol as in patients. Results Forty-six lesions were identified. There was a significant correlation of maximum and mean SUVs derived from PET and PET/CT for 14 paradiaphragmatic lesions (r=0.97 respectively; p<0.001 respectively) and for 32 lesions located distant from the diaphragm (r=0.87 and r=0.89 respectively; p<0.001 respectively). No significant differences were observed in the SUVs calculated with PET and PET/CT in the lesions or in the organs. In the phantom, radioactivity concentration in spheres calculated from PET and from PET/CT correlated significantly (r=0.99; p<0.001). Conclusion SUVs of cancer lesions and normal organs were comparable between PET and PET/CT, supporting the usefulness of PET/CT-derived SUVs for quantification of tumour metabolism.     

Correction for oral contrast artifacts in CT attenuation-corrected PET images obtained by combined PET/CT.

Recent studies have shown increased artifacts in CT attenuation-corrected (CTAC) PET images acquired with oral contrast agents because of misclassification of contrast as bone. We have developed an algorithm, segmented contrast correction (SCC), to properly transform CT numbers in the contrast regions from CT energies (40-140 keV) to PET energy at 511 keV. METHODS: A bilinear transformation, equivalent to that supplied by the PET/CT scanner manufacturer, for the conversion of linear attenuation coefficients of normal tissues from CT to PET energies was optimized for BaSO(4) contrast agent. This transformation was validated by comparison with the linear attenuation coefficients measured for BaSO(4) at concentrations ranging from 0% to 80% at 511 keV for PET transmission images acquired with (68)Ge rod sources. In the CT images, the contrast regions were contoured to exclude bony structures and then segmented on the basis of a minimum threshold CT number (300 Hounsfield units). The CT number in each pixel identified with contrast was transformed into the corresponding effective bone CT number to produce the correct attenuation coefficient when the data were translated by the manufacturer software into PET energy during the process of CT attenuation correction. CT images were then used for attenuation correction of PET emission data. The algorithm was validated with a phantom in which a lesion was simulated within a volume of BaSO(4) contrast and in the presence of a human vertebral bony structure. Regions of interest in the lesion, bone, and contrast on emission PET images reconstructed with and without the SCC algorithm were analyzed. The results were compared with those for images obtained with (68)Ge-based transmission attenuation-corrected PET. RESULTS: The SCC algorithm was able to correct for contrast artifacts in CTAC PET images. In the phantom studies, the use of SCC resulted in an approximate 32% reduction in the apparent activity concentration in the lesion compared with data obtained from PET images without SCC and a <7.6% reduction compared with data obtained from (68)Ge-based attenuation-corrected PET images. In one clinical study, maximum standardized uptake value (SUV(max)) measurements for the lesion, bladder, and bowel were, respectively, 14.52, 13.63, and 13.34 g/mL in CTAC PET images, 59.45, 26.71, and 37.22 g/mL in (68)Ge-based attenuation-corrected PET images, and 11.05, 6.66, and 6.33 g/mL in CTAC PET images with SCC. CONCLUSION: Correction of oral contrast artifacts in PET images obtained by combined PET/CT yielded more accurate quantitation of the lesion and other, normal structures. The algorithm was tested in a clinical case, in which SUV(max) measurements showed discrepancies of 2%, 1.3%, and 5% between (68)Ge-based attenuation-corrected PET images and CTAC PET images with SCC for the lesion, bladder, and bowel, respectively. These values correspond to 6.5%, 62%, and 66% differences between CTAC-based measurements and (68)Ge-based ones.     

PET recognition of pulmonary metastases on PET/CT imaging: impact of attenuation-corrected and non-attenuation-corrected PET images

Purpose The aims of this study were to assess the performance of FDG PET at PET/CT imaging for the detection of pulmonary metastases and to evaluate differences in lesion detectability on attenuation-corrected (AC) and non-attenuation corrected (NAC) PET images.Methods The institutional PET/CT database was searched for patients with pulmonary metastases of 3–60 mm in diameter. Ninety-two patients with 438 metastases to the lungs were included in the study. The primary tumours were 33 malignant melanomas, 12 carcinomas of unknown primary, 11 colorectal carcinomas, eight differentiated thyroid carcinomas, seven aggressive non-Hodgkins lymphomas, six head and neck cancers, three breast cancers, two prostate cancers and ten others. Lesion detectability was visually compared between PET and CT and between AC and NAC PET images using a five-point scale.Results Of the 438 pulmonary metastases, 174 were detected with FDG PET (39.7%), six of them on NAC images only (not significant). Visual scores were higher on NAC images in 41.4% and equal in 54.6% of lesions. The sensitivity of FDG PET increased significantly from 0.405 for metastases of 5–7 mm in diameter to 0.784 for lesions of 8–10 mm and to 0.935 for lesions measuring 11–29 mm in diameter. No metastases smaller than 5 mm in diameter were seen on PET images.Conclusion FDG PET/CT is useful for the assessment of pulmonary metastases. The frequency of lesion detection is similar for AC and NAC PET images. A reduced sensitivity of FDG PET has to be considered for lesions smaller than 11 mm in diameter.     

Discrimination and anatomical mapping of PET-positive lesions: comparison of CT attenuation-corrected PET images with coregistered MR and CT images in the abdomen

Purpose

PET/MR has the potential to become a powerful tool in clinical oncological imaging. The purpose of this prospective study was to evaluate the performance of a single T1-weighted (T1w) fat-suppressed unenhanced MR pulse sequence of the abdomen in comparison with unenhanced low-dose CT images to characterize PET-positive lesions.

Methods

A total of 100 oncological patients underwent sequential whole-body ¹⁸F-FDG PET with CT-based attenuation correction (AC), 40?mAs low-dose CT and two-point Dixon-based T1w 3D MRI of the abdomen in a trimodality PET/CT-MR system. PET-positive lesions were assessed by CT and MRI with regard to their anatomical location, conspicuity and additional relevant information for characterization.

Results

From among 66 patients with at least one PET-positive lesion, 147 lesions were evaluated. No significant difference between MRI and CT was found regarding anatomical lesion localization. The MR pulse sequence used performed significantly better than CT regarding conspicuity of liver lesions (p?<?0.001, Wilcoxon signed ranks test), whereas no difference was noted for extrahepatic lesions. For overall lesion characterization, MRI was considered superior to CT in 40?% of lesions, equal to CT in 49?%, and inferior to CT in 11?%.

Conclusion

Fast Dixon-based T1w MRI outperformed low-dose CT in terms of conspicuity and characterization of PET-positive liver lesions and performed similarly in extrahepatic tumour manifestations. Hence, under the assumption that the technical issue of MR AC for whole-body PET examinations is solved, in abdominal PET/MR imaging the replacement of low-dose CT by a single Dixon-based MR pulse sequence for anatomical lesion correlation appears to be valid and robust.     

Focal tracer uptake: a potential artifact in contrast-enhanced dual-modality PET/CT scans.

This study was performed to evaluate a possible artifact related to the administration of intravascular contrast agent in dual-modality PET/CT imaging. METHODS: Thirty oncology patients underwent whole-body PET/CT. CT images, which were collected in the presence of intravenous and oral iodinated contrast agent, were used for PET attenuation correction. PET images were assessed for the artifact, defined as a region of high count rate on attenuation-corrected images in accurate coregistration with a contrast-enhanced blood vessel. Intravascular enhancement of thoracic veins was quantified by application of regions of interest, and quantities in patients with the artifact (group 1) and without the artifact (group 2) were correlated. Body surface area was calculated for all patients. RESULTS: The contrast-induced PET artifact was present in 4 (13%) of 30 patients. Mean density differences in intravascular enhancement were highly significant (P < 0.001) in a comparison of group 1 (2,262 +/- 304 Hounsfield units [HU]) and group 2 (1,058 +/- 209 HU). Body surface area was significantly lower (P = 0.035) in the patients of group 1 (1.67 +/- 0.11 m(2)) than in the patients of group 2 (2.01 +/- 0.18 m(2)). CONCLUSION: Contrast-enhanced dual-modality PET/CT examinations may result in a PET artifact that is due to the transient bolus passage of undiluted intravenous contrast agent.     

Attenuation correction of PET images with respiration-averaged CT images in PET/CT.

Attenuation correction (AC) of PET images with helical CT (HCT) in PET/CT matches only the spatial resolution of CT and PET, not the temporal resolution. We therefore proposed the use of respiration-averaged CT (ACT) to match the temporal resolution of CT and PET and evaluated the improvement of tumor quantification in PET images of the thorax with ACT. METHODS: First, we examined 100 consecutive clinical PET/CT studies for the frequency and magnitude of misalignment at the diaphragm position between the HCT and the PET data. Patients were injected with 555-740 MBq of (18)F-FDG and scanned 1 h after injection. The HCT data were acquired at the following settings: 120 kV, 300 mA, pitch of 1.35:1, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. Patients were instructed to hold their breath at midexpiration during HCT of the thorax. The PET acquisition was 3 min per bed. Second, we retrospectively analyzed studies of 8 patients (1 with esophageal cancer and 7 with lung cancer). Each study included regular PET/CT followed by 4-dimensional (4D) CT for radiation treatment planning. We compared the results of AC of the PET data with HCT and ACT. There were 13 tumors in these 8 patients. The 4D CT data were acquired at the following settings: 120 kV, 50-150 mA, cine duration of 1 breathing cycle plus 1 s, collimation of 8 x 1.25 mm, and rotation cycle of 0.5 s. The acquisition was taken when the patient was in the free-breathing state. We averaged the 10 phases of the 4D CT data to obtain ACT for AC of the PET data. Both the ACT and the HCT data were used for AC of the same PET data. RESULTS: There was a misalignment between the HCT and the PET data in 50 of 100 patient studies. In 34 studies, the misalignment was greater than 2 cm. In a comparison of HCT and ACT, 5 tumors had differences in standardized uptake values (SUV) between HCT-and ACT-attenuation-corrected PET of less than 20%, and 4 tumors had differences in SUV of more than 50%. The latter 4 tumors were found in the patient with esophageal cancer and in 2 of the patients with lung cancer. The PET data from these 3 patients had a misalignment of 2-4.5 cm relative to the HCT data. Breathing artifacts were significantly reduced by ACT. Seven of the 8 patients had a lower diaphragm position on HCT than on ACT, suggesting that the patients tended to hold a deeper breath during HCT than during ACT. CONCLUSION: The high rate of misalignment suggested a potential mismatch between the HCT and the PET data with the limited-breath-hold CT protocol. In the comparison of HCT and ACT, significant differences (>50%) in SUV were attributable to different breathing states between HCT and PET. The PET data corrected by ACT did not show breathing artifacts, suggesting that ACT may be more accurate than HCT for AC of the PET data.     

Comparison of lesion detection and quantitation of tracer uptake between PET from a simultaneously acquiring whole-body PET/MR hybrid scanner and PET from PET/CT

Purpose

PET/MR hybrid scanners have recently been introduced, but not yet validated. The aim of this study was to compare the PET components of a PET/CT hybrid system and of a simultaneous whole-body PET/MR hybrid system with regard to reproducibility of lesion detection and quantitation of tracer uptake.

Methods

A total of 46 patients underwent a whole-body PET/CT scan 1?h after injection and an average of 88?min later a second scan using a hybrid PET/MR system. The radioactive tracers used were ¹⁸F-deoxyglucose (FDG), ¹⁸F-ethylcholine (FEC) and ⁶⁸Ga-DOTATATE (Ga-DOTATATE). The PET images from PET/CT (PET_CT) and from PET/MR (PET_MR) were analysed for tracer-positive lesions. Regional tracer uptake in these foci was quantified using volumes of interest, and maximal and average standardized uptake values (SUV_max and SUV_avg, respectively) were calculated.

Results

Of the 46 patients, 43 were eligible for comparison and statistical analysis. All lesions except one identified by PET_CT were identified by PET_MR (99.2?%). In 38 patients (88.4?%), the same number of foci were identified by PET_CT and by PET_MR. In four patients, more lesions were identified by PET_MR than by PET_CT, in one patient PET_CT revealed an additional focus compared to PET_MR. The mean SUV_max and SUV_avg of all lesions determined by PET_MR were by 21?% and 11?% lower, respectively, than the values determined by PET_CT (p?<?0.05), and a strong correlation between these variables was identified (Spearman rho 0.835; p?<?0.01).

Conclusion

PET/MR showed equivalent performance in terms of qualitative lesion detection to PET/CT. The differences demonstrated in quantitation of tracer uptake between PET_CT and PET_MR were minor, but statistically significant. Nevertheless, a more detailed study of the quantitative accuracy of PET_MR and the factors governing it is needed to ultimately assess its accuracy in measuring tissue tracer concentrations.     

Assessment of malignant skeletal disease: initial experience with 18F-fluoride PET/CT and comparison between 18F-fluoride PET and 18F-fluoride PET/CT.

18F-fluoride PET/CT was performed on 44 oncologic patients to evaluate its diagnostic accuracy in assessing malignant osseous involvement and in differentiating malignant from benign bone lesions. METHODS: (18)F-fluoride PET and (18)F-fluoride PET/CT were interpreted separately. Lesions showing increased (18)F-fluoride uptake were categorized as malignant, benign, or inconclusive. The final diagnosis of lesions was based on histopathology, correlation with contemporaneous diagnostic CT or MRI, or clinical follow-up of at least 6 mo (mean, 10 +/- 3 mo). RESULTS: Increased (18)F-fluoride uptake was detected at 212 sites, including 111 malignant lesions, 89 benign lesions, and 12 lesions for which the final diagnosis could not be determined. In a lesion-based analysis, the sensitivity of PET alone in differentiating benign from malignant bone lesions was 72% when inconclusive lesions were considered false negative and 90% when inconclusive lesions were considered true positive. On PET/CT, 94 of 111 (85%) metastases presented as sites of increased uptake with corresponding lytic or sclerotic changes, and 16 of the 17 remaining metastases showed normal-appearing bone on CT, for an overall sensitivity of 99% for tumor detection. For only 1 metastasis was PET/CT misleading, suggesting the false diagnosis of a benign lesion. The specificity of PET/CT was significantly higher than that of PET alone (97% vs. 72%, P < 0.001). PET/CT identified benign abnormalities at the location exactly corresponding to the scintigraphic increased uptake for 85 of 89 (96%) benign lesions. In a patient-based analysis, the sensitivity of PET and PET/CT was 88% and 100%, respectively (P < 0.05) and the specificity was 56% and 88%, respectively (not statistically significant). Among the 12 patients referred for (18)F-fluoride assessment because of bone pain despite negative findings on (99m)Tc-methylene diphosphonate bone scintigraphy, (18)F-fluoride PET/CT suggested malignant bone involvement in all 4 patients with proven skeletal metastases, a potential benign cause in 4 of 7 patients who had no evidence of metastatic disease, and a soft-tissue tumor mass invading a sacral foramen in 1 patient. CONCLUSION: The results indicate that (18)F-fluoride PET/CT is both sensitive and specific for the detection of lytic and sclerotic malignant lesions. It accurately differentiated malignant from benign bone lesions and possibly assisted in identifying a potential cause for bone pain in oncologic patients. For most lesions, the anatomic data provided by the low-dose CT of the PET/CT study obviates the performance of full-dose diagnostic CT for correlation purposes.     

Pulmonary FDG uptake without a CT counterpart - a pitfall in interpreting PET/CT images

Abnormal pulmonary 18F-FDG foci may occur with benign lesions like pneumonia but seldomly without any pathological CT findings. We report the case of a focal pulmonary 18F-FDG uptake without CT correlate in an initial staging examination of a patient with squamous cell carcinoma of the base of the tongue. A follow-up study did not show any suspicious lesion in this area, but pneumonia with 18F-FDG uptake in another region of the lung. 18F-FDG foci without pathological CT are a rare finding and have been associated with emboli. In the literature two main mechanisms underlying focal 18F-FDG uptake in pulmonary embolism are mentioned: an inflammatory reaction of a pre-existing vascular thrombus and an iatrogenic microembolism caused during injection. In our case the 18F-FDG accumulation was assessed as an iatrogenic pulmonary microembolism.     

A retrospective comparison between 68Ga-DOTA-TOC PET/CT and 18F-DOPA PET/CT in patients with extra-adrenal paraganglioma

Purpose

¹⁸F-Fluoro-l-dihydroxyphenylalanine (¹⁸F-DOPA) PET offers high sensitivity and specificity in the imaging of nonmetastatic extra-adrenal paragangliomas (PGL) but lower sensitivity in metastatic or multifocal disease. These tumours are of neuroendocrine origin and can be detected by ⁶⁸Ga-DOTA-Tyr³-octreotide (⁶⁸Ga-DOTA-TOC) PET. Therefore, we compared ⁶⁸Ga-DOTA-TOC and ¹⁸F-DOPA as radiolabels for PET/CT imaging for the diagnosis and staging of extra-adrenal PGL. Combined cross-sectional imaging was the reference standard.

Methods

A total of 5 men and 15 women (age range 22 to 73 years) with anatomical and/or histologically proven extra-adrenal PGL were included in this study. Of these patients, 5 had metastatic or multifocal lesions and 15 had single sites of disease. Comparative evaluation included morphological imaging with CT and functional imaging with ⁶⁸Ga-DOTA-TOC PET and ¹⁸F-DOPA PET. The imaging results were analysed on a per-patient and a per-lesion basis. The maximum standardized uptake value (SUV_max) of each functional imaging modality in concordant tumour lesions was measured.

Results

Compared with anatomical imaging, ⁶⁸Ga-DOTA-TOC PET and ¹⁸F-DOPA PET each had a per-patient and per-lesion detection rate of 100 % in nonmetastatic extra-adrenal PGL. However, in metastatic or multifocal disease, the per-lesion detection rate of ⁶⁸Ga-DOTA-TOC was 100 % and that of ¹⁸F-DOPA PET was 56.0 %. Overall, ⁶⁸Ga-DOTA-TOC PET identified 45 lesions; anatomical imaging identified 43 lesions, and ¹⁸F-DOPA PET identified 32 lesions. The overall per-lesion detection rate of ⁶⁸Ga-DOTA-TOC PET was 100 % (McNemar, P?<?0.5), and that of ¹⁸F-DOPA PET was 71.1 % (McNemar, P?<?0.001). The SUV_max (mean ± SD) of all 32 concordant lesions was 67.9?±?61.5 for ⁶⁸Ga-DOTA-TOC PET and 11.8?±?7.9 for ¹⁸F-DOPA PET (Mann-Whitney U test, P?<?0.0001).

Conclusion

⁶⁸Ga-DOTA-TOC PET may be superior to ¹⁸F-DOPA PET and diagnostic CT in providing valuable information for pretherapeutic staging of extra-adrenal PGL, particularly in surgically inoperable tumours and metastatic or multifocal disease.     

Non-malignant FDG uptake in infradiaphragmatic adipose tissue: a new site of physiological tracer biodistribution characterised by PET/CT

The purpose of this study was to characterise a benign pattern of infradiaphragmatic ¹⁸F-fluorodeoxyglucose (FDG) uptake in cancer patients using PET/CT. Infradiaphragmatic foci of FDG uptake, localised by PET/CT in regions of normal fat tissues, were demonstrated, in conjunction with fatty uptake in the neck and shoulders, in 9 of 1,241 (0.7%) patients. The imaging and clinical characteristics of this pattern and its possible clinical significance were assessed. PET/CT precisely localised infradiaphragmatic fat uptake (IDFU) within normal retroperitoneal fatty tissue of the perirenal space (nine patients) and in the paracolic or parahepatic space (four patients). Perirenal uptake was bilateral in five patients and focal in six. Paracolic and parahepatic uptake was bilateral in three patients and linear in all four patients. There was no evidence of malignancy at any of the sites during a follow-up period of 9–21 months. IDFU was significantly more prevalent in young patients assessed for monitoring response to therapy, and was always associated with the benign supradiaphragmatic uptake pattern, although its prevalence was significantly lower. There were no significant differences between the clinical characteristics of these two patterns of benign fatty FDG uptake. It is concluded that PET/CT allows for precise identification of increased FDG uptake in abdominal fatty tissue and further exclusion of disease at such sites. This benign uptake may represent increased glucose consumption in activated brown adipose tissue, similar to the mechanism suggested for supradiaphragmatic uptake. Recognition of this benign IDFU pattern is important for correct interpretation of abdominal PET findings in cancer patients.     

Integrated PET/CT in the preoperative staging of lung cancer: A prospective comparison of CT,PET and integrated PET/CT

Purpose

The purpose of this study was to evaluate the role of integrated PET/CT in the staging of lung cancer compared with CT alone or PET alone.

Materials and methods

Thirty-three patients underwent integrated PET/CT for the staging of lung cancer. The tumor, node and metastasis (TNM) stages were assessed with CT, PET and integrated PET–CT and compared with the surgical and pathological staging.

Results

CT correctly evaluated the (T) status in (64%) of the patients, PET in (59%) and PET/CT in (86%). CT correctly evaluated the (N) status in (73%) of the patients, PET in (76%), and PET/CT (88%) with accuracy, sensitivity, specificity, PPV and NPV were 73%, 78%, 71%, 50% and 94% for CT, 76%, 67%, 79%, 55% and 95% for PET and 88%, 89%, 88%, 73% and 100% for PET/CT respectively, and for (M) status were 91%, 86%, 92%, 75% and 96% for CT, 88%, 71%, 92%, 71% and 92% for PET and 97%, 100%, 96%, 88% and 100% for PET/CT respectively. Regarding the overall TNM staging CT correctly staged 24 patients. PET correctly staged 23 cases while PET/CT correctly staged 30 cases. A significant difference in the accuracy of overall tumor staging between PET/CT and CT (P = 0.0412) or PET (P = 0.0233).

Conclusion

The integrated PET/CT is superior to either CT or PET in the staging of lung cancer which has an important impact on selection of the appropriate treatment regimen.     

PET/CT in lymphoma: prospective study of enhanced full-dose PET/CT versus unenhanced low-dose PET/CT.

PET/CT combines functional and morphologic data and increases diagnostic accuracy in a variety of malignancies. This study prospectively compares the agreement between contrast-enhanced full-dose PET/CT and unenhanced low-dose PET/CT in lesion detection and initial staging of Hodgkin's disease and non-Hodgkin's lymphoma. METHODS: Forty-seven biopsy-proven lymphoma patients underwent a 18F-FDG PET/CT study that included unenhanced low-dose CT and enhanced full-dose CT for initial staging. Patients who had undergone previous diagnostic CT for initial staging were excluded. For every patient, each modality of PET/CT images was evaluated by either of 2 pairs of readers, with each pair comprising 1 experienced radiologist and 1 experienced nuclear physician. While evaluating one of the 2 types of PET/CT, the readers were unaware of the results of the other type. Lesion detection, number of sites affected in each anatomic region, and disease stage were assessed. Agreement between techniques was determined by the kappa-statistic, and discordances were studied by the McNemar test. Clinical, analytic, histopathologic, diagnostic CT, and PET data; data from other imaging techniques; and follow-up data constituted the reference standard. RESULTS: For region-based analysis, no significant differences were found between unenhanced low-dose PET/CT and contrast-enhanced full-dose PET/CT, although full-dose PET/CT showed fewer indeterminate findings and a higher number of extranodal sites affected than did low-dose PET/CT. Agreement between the 2 types of PET/CT was almost perfect for disease stage (kappa = 0.92; P < 0.001). CONCLUSION: Our study showed a good correlation between unenhanced low-dose PET/CT and contrast-enhanced full-dose PET/CT for lymph node and extranodal disease in lymphomas, suggesting that unenhanced low-dose PET/CT might suffice in most patients as the only imaging technique for the initial staging of lymphomas, reserving diagnostic CT for selected cases.     

Metallic artifacts caused by dental metal prostheses on PET images: a PET/CT phantom study using different PET/CT scanners

Objective  The objective of this study was to investigate the effects of computed tomography (CT) artifacts caused by dental metal prostheses on positron emission tomography (PET) images. Methods  A dental arch cast was fixed in a cylindrical water-bath phantom. A spherical phantom positioned in the vicinity of the dental arch cast was used to simulate a tumor. To simulate the tumor imaging, the ratio of the ¹⁸F-fluoro-deoxy-glucose radioactivity concentration of the spherical phantom to that of the water-bath phantom was set at 2.5. A dental bridge composed of a gold–silver–palladium alloy on the right mandibular side was prepared. A spherical phantom was set in the white artifact area on the CT images (site A), in a slightly remote area from the white artifact (site B), and in a black artifact area (site C). A PET/CT scan was performed with and without the metal bridge at each simulated tumor site, and the artifactual influence was evaluated on the axial attenuation-corrected (AC) PET images, in which the simulated tumor produced the strongest accumulation. Measurements were performed using three types of PET/CT scanners (scanners 1 and 2 with CT-based attenuation correction, and 3 with Cesium-137 (¹³⁷Cs)-based attenuation correction). The influence of the metal bridge was evaluated using the change rate of the SUVmean with and without the metal bridge. Results  At site A, an overestimation was shown (scanner 1: +5.0% and scanner 2: +2.5%), while scanner 3 showed an underestimation of −31.8%. At site B, an overestimation was shown (scanner 1: +2.1% and scanner 2: +2.0%), while scanner 3 showed an underestimation of −2.6%. However, at site C, an underestimation was shown (scanner 1: −25.0%, scanner 2: −32.4%, and scanner 3: −8.4%). Conclusions  When CT is used for attenuation correction in patients with dental metal prostheses, an underestimation of radioactivity of accumulated tracer is anticipated in the dark streak artifact area on the CT images. In this study, the dark streak artifacts of the CT caused by metallic dental prostheses may cause false negative finding of PET/CT in detecting small and/or low uptake tumor in the oral cavity.