Value of a Dixon-based MR/PET attenuation correction sequence for the localization and evaluation of PET-positive lesions

Purpose

In this study, the potential contribution of Dixon-based MR imaging with a rapid low-resolution breath-hold sequence, which is a technique used for MR-based attenuation correction (AC) for MR/positron emission tomography (PET), was evaluated for anatomical correlation of PET-positive lesions on a 3T clinical scanner compared to low-dose CT. This technique is also used in a recently installed fully integrated whole-body MR/PET system.

Methods

Thirty-five patients routinely scheduled for oncological staging underwent ¹⁸F-fluorodeoxyglucose (FDG) PET/CT and a 2-point Dixon 3-D volumetric interpolated breath-hold examination (VIBE) T1-weighted MR sequence on the same day. Two PET data sets reconstructed using attenuation maps from low-dose CT (PET_{AC_CT}) or simulated MR-based segmentation (PET_{AC_MR}) were evaluated for focal PET-positive lesions. The certainty for the correlation with anatomical structures was judged in the low-dose CT and Dixon-based MRI on a 4-point scale (0?C3). In addition, the standardized uptake values (SUVs) for PET_{AC_CT} and PET_{AC_MR} were compared.

Results

Statistically, no significant difference could be found concerning anatomical localization for all 81 PET-positive lesions in low-dose CT compared to Dixon-based MR (mean 2.51?±?0.85 and 2.37?±?0.87, respectively; p?=?0.1909). CT tended to be superior for small lymph nodes, bone metastases and pulmonary nodules, while Dixon-based MR proved advantageous for soft tissue pathologies like head/neck tumours and liver metastases. For the PET_{AC_CT}- and PET_{AC_MR}-based SUVs (mean 6.36?±?4.47 and 6.31?±?4.52, respectively) a nearly complete concordance with a highly significant correlation was found (r?=?0.9975, p?Conclusion Dixon-based MR imaging for MR AC allows for anatomical allocation of PET-positive lesions similar to low-dose CT in conventional PET/CT. Thus, this approach appears to be useful for future MR/PET for body regions not fully covered by diagnostic MRI due to potential time constraints.     

Evaluation of the PET component of simultaneous [18F]choline PET/MRI in prostate cancer: comparison with [18F]choline PET/CT

Purpose

The aim of this study was to evaluate the positron emission tomography (PET) component of [¹⁸F]choline PET/MRI and compare it with the PET component of [¹⁸F]choline PET/CT in patients with histologically proven prostate cancer and suspected recurrent prostate cancer.

Methods

Thirty-six patients were examined with simultaneous [¹⁸F]choline PET/MRI following combined [¹⁸F]choline PET/CT. Fifty-eight PET-positive lesions in PET/CT and PET/MRI were evaluated by measuring the maximum and mean standardized uptake values (SUV_max and SUV_mean) using volume of interest (VOI) analysis. A scoring system was applied to determine the quality of the PET images of both PET/CT and PET/MRI. Agreement between PET/CT and PET/MRI regarding SUV_max and SUV_mean was tested using Pearson’s product-moment correlation and Bland-Altman analysis.

Results

All PET-positive lesions that were visible on PET/CT were also detectable on PET/MRI. The quality of the PET images was comparable in both groups. Median SUV_max and SUV_mean of all lesions were significantly lower in PET/MRI than in PET/CT (5.2 vs 6.1, p?<?0.05 and 2.0 vs 2.6, p?<?0.001, respectively). Pearson’s product-moment correlation indicated highly significant correlations between SUV_max of PET/CT and PET/MRI (R?=?0.86, p?<?0.001) as well as between SUV_mean of PET/CT and PET/MRI (R?=?0.81, p?<?0.001). Bland-Altman analysis revealed lower and upper limits of agreement of ?2.77 to 3.64 between SUV_max of PET/CT vs PET/MRI and ?1.12 to +2.23 between SUV_mean of PET/CT vs PET/MRI.

Conclusion

PET image quality of PET/MRI was comparable to that of PET/CT. A highly significant correlation between SUV_max and SUV_mean was found. Both SUV_max and SUV_mean were significantly lower in [¹⁸F]choline PET/MRI than in [¹⁸F]choline PET/CT. Differences of SUV_max and SUV_mean might be caused by different techniques of attenuation correction. Furthermore, differences in biodistribution and biokinetics of [¹⁸F]choline between the subsequent examinations and in the respective organ systems have to be taken into account.     

Diagnostic accuracy of 68Ga-DOTANOC PET/CT imaging in pheochromocytoma

Purpose

The purpose of the present study was to evaluate the diagnostic accuracy of ⁶⁸Ga-DOTANOC positron emission tomography (PET)/CT in patients with suspicion of pheochromocytoma.

Methods

Data of 62 patients [age 34.3?±?16.1 years, 14 with multiple endocrine neoplasia type 2 (MEN2)] with clinical/biochemical suspicion of pheochromocytoma and suspicious adrenal lesion on contrast CT (n?=?70), who had undergone ⁶⁸Ga-DOTANOC PET/CT, were retrospectively analyzed. PET/CT images were analyzed visually as well as semiquantitatively, with measurement of maximum standardized uptake value (SUV_max), SUV_mean, SUV_max/SUV_liver, and SUV_mean/SUV_liver. Results of PET/CT were compared with ¹³¹I-metaiodobenzylguanidine (MIBG) imaging, which was available in 40 patients (45 lesions). Histopathology and/or imaging/clinical/biochemical follow-up (minimum 6 months) was used as reference standard.

Results

The sensitivity, specificity, and accuracy of ⁶⁸Ga-DOTANOC PET/CT was 90.4, 85, and 88.7 %, respectively, on patient-based analysis and 92, 85, and 90 %, respectively, on lesion-based analysis. ⁶⁸Ga-DOTANOC PET/CT showed 100 % accuracy in patients with MEN2 syndrome and malignant pheochromocytoma. On direct comparison, lesion-based accuracy of ⁶⁸Ga-DOTANOC PET/CT for pheochromocytoma was significantly higher than ¹³¹I-MIBG imaging (91.1 vs 66.6 %, p?=?0.035). SUV_max was higher for pheochromocytomas than other adrenal lesions (p?=?0.005), MEN2-associated vs sporadic pheochromocytoma (p?=?0.012), but no difference was seen between benign vs malignant pheochromocytoma (p?=?0.269).

Conclusion

⁶⁸Ga-DOTANOC PET/CT shows high diagnostic accuracy in patients with suspicion of pheochromocytoma and is superior to ¹³¹I-MIBG imaging for this purpose. Best results of ⁶⁸Ga-DOTANOC PET/CT are seen in patients with MEN2-associated and malignant pheochromocytoma.     

Evaluation of intratumoural heterogeneity on 18F-FDG PET/CT for characterization of peripheral nerve sheath tumours in neurofibromatosis type 1

Purpose

The aim of the study was to evaluate the potential usefulness of intratumoural tracer uptake heterogeneity on ¹⁸F-fluorodeoxyglucose (FDG) positron emission tomography (PET)/CT as compared to a cut-off maximum standardized uptake value (SUV_max) for characterization of peripheral nerve sheath tumours (PNSTs) in neurofibromatosis type 1 (NF1).

Methods

Fifty patients suffering from NF1 were examined by ¹⁸F-FDG PET/CT. Intralesional tracer uptake was analysed qualitatively and semi-quantitatively by measuring the mean and maximum SUV. Uptake heterogeneity was graded qualitatively using a three-point scale and semi-quantitatively by calculating an SUV-based heterogeneity index (HI_SUV). Cohen’s κ was used to determine inter- and intra-rater agreement. Histopathological evaluation and clinical as well as radiological follow-up examinations served as the reference standards.

Results

A highly significant correlation between the degree of intratumoural uptake heterogeneity on ¹⁸F-FDG PET and malignant transformation of PNSTs was observed (p?<?0.0001). Semi-quantitative HI_SUV was significantly higher in malignant PNSTs (MPNSTs) than in benign tumours (p?=?0.0002). Both intralesional heterogeneity and SUV_max could be used to identify malignant tumours with a sensitivity of 100 %. Cohen’s κ was 0.86 for inter-rater agreement and 0.88 for intra-rater agreement on heterogeneity.

Conclusion

MPNSTs in patients with NF1 demonstrate considerable intratumoural uptake heterogeneity on ¹⁸F-FDG PET/CT. Assessment of tumour heterogeneity is highly reproducible. Both tumour heterogeneity and a cut-off SUV_max may be used to sensitively identify malignant PNSTs, but the specificity is higher for the latter. A combination of both methods leads to a non-significant improvement in diagnostic performance.     

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.     

Prospective evaluation of solitary thyroid nodule on 18F-FDG PET/CT and high-resolution ultrasonography

Purpose

The utility of 18F-FDG PET/CT in the assessment of thyroid nodules is unclear as there are several conflicting reports on the usefulness of SUV as an indicator to distinguish benign from malignant thyroid lesions. This study incorporated an additional parameter, namely dual time point imaging, to determine the diagnostic accuracy of PET/CT imaging. The performance of 18F-FDG PET/CT was compared to that of high-resolution ultrasound which is routinely used for the evaluation of thyroid nodules.

Methods

Two hundred patients with incidentally detected solitary thyroid nodules were included in the study. Each patient underwent ultrasound and PET/CT evaluation within 7 days of each other, reported by an experienced radiologist and nuclear medicine specialist, respectively, in a blinded manner. The PET/CT criteria employed were maximum SUV (SUV_max) at 60 min and change in SUV_max at delayed (120 min) imaging. Final diagnosis was based on pathological evaluation and follow-up.

Results

Of the 200 patients, 26 had malignant and 174 had benign nodules. The sensitivity, specificity, positive predictive value (PPV), negative predictive value (NPV) and accuracy of ultrasound were 80.8, 81.6, 39.6, 96.6 and 81.5%, respectively. Using SUV_max at 60 min as the diagnostic criterion, the above indices were 80.8, 84.5, 43.8, 96.7 and 84%, respectively, for PET/CT. The SUV_max of malignant thyroid lesions was significantly higher than benign lesions (16.2 ± 10.6 vs. 4.5 ± 3.1, respectively; p = 0.0001). Incorporation of percentage change in SUV_max at delayed imaging as the diagnostic criterion yielded a slightly improved sensitivity, specificity, PPV, NPV and accuracy of 84.6, 85.6, 46.8, 97.4 and 85.5%, respectively. There was a significant difference in percentage change in SUV_max between malignant and benign thyroid lesions (14.9 ± 11.4 vs. ?1.6 ± 13.7, respectively; p = 0.0001). However, there was no statistically significant difference (95% confidence interval) between the diagnostic performance of PET/CT and ultrasound.

Conclusions

Routine use of 18F-FDG PET/CT with SUV_max at 60 min as the sole diagnostic criterion does not appear to have a significant advantage over high-resolution ultrasound in the evaluation of thyroid nodules. Incorporation of dual time point imaging enhances image interpretation, and yields a higher diagnostic performance, yet it is not statistically significant. Bearing in mind the cost, limited availability and radiation exposure, routine use of 18F-FDG PET/CT for distinguishing benign from malignant thyroid nodules cannot be recommended.     

Preoperative lymph node staging in patients with primary prostate cancer: comparison and correlation of quantitative imaging parameters in diffusion-weighted imaging and 11C-choline PET/CT

Purpose

To compare the diagnostic performance of DWI and 11C-choline PET/CT in the assessment of preoperative lymph node status in patients with primary prostate cancer.

Material and methods

Thirty-three patients underwent DWI and 11C-choline PET/CT prior to prostatectomy and extended pelvic lymph node dissection. Mean standardised uptake value (SUV_mean) and mean apparent diffusion coefficient (ADC) of 76 identified lymph nodes (LN) were measured and correlated with histopathology. ADC values and SUVs were compared using linear regression analysis.

Results

A significant difference between benign and malignant LN was observed for ADC values (1.17 vs. 0.96?×?10^-3 mm²/s; P?<?0.001) and SUV_mean (1.61 vs. 3.20; P?<?0.001). ROC analysis revealed an optimal ADC threshold of 1.01?×?10^-3 mm²/s for differentiating benign from malignant LN with corresponding sensitivity/specificity of 69.70 %/78.57 % and an area under the curve (AUC) of 0.785. The optimal threshold for SUV_mean was 2.5 with corresponding sensitivity/specificity of 69.72 %/90.48 % and with an AUC of 0.832. ADC values and SUV_mean showed a moderate significant inverse correlation (r?=?-0.63).

Conclusion

Both modalities reveal similar moderate diagnostic performance for preoperative lymph node staging of prostate cancer, not justifying their application in routine clinical practice at this time. The only moderate inverse correlation between ADC values and SUV_mean suggests that both imaging parameters might provide complementary information on tumour biology.

Key Points

? Conventional imaging shows low performance for lymph node staging in prostate cancer. ? DWI and 11C-choline PET/CT both provide additional functional information ? Both functional modalities reveal only moderate diagnostic performance.     

Comparison of integrated whole-body [11C]choline PET/MR with PET/CT in patients with prostate cancer

Purpose

To evaluate the performance of conventional [¹¹C]choline PET/CT in comparison to that of simultaneous whole-body PET/MR.

Methods

The study population comprised 32 patients with prostate cancer who underwent a single-injection dual-imaging protocol with PET/CT and subsequent PET/MR. PET/CT scans were performed applying standard clinical protocols (5 min after injection of 793?±?69 MBq [¹¹C]choline, 3 min per bed position, intravenous contrast agent). Subsequently (52?±?15 min after injection) PET/MR was performed (4 min per bed position). PET images were reconstructed iteratively (OSEM 3D), scatter and attenuation correction of emission data and regional allocation of [¹¹C]choline foci were performed using CT data for PET/CT and segmented Dixon MR, T1 and T2 sequences for PET/MR. Image quality of the respective PET scans and PET alignment with the respective morphological imaging modality were compared using a four point scale (0–3). Furthermore, number, location and conspicuity of the detected lesions were evaluated. SUVs for suspicious lesions, lung, liver, spleen, vertebral bone and muscle were compared.

Results

Overall 80 lesions were scored visually in 29 of the 32 patients. There was no significant difference between the two PET scans concerning number or conspicuity of the detected lesions (p not significant). PET/MR with T1 and T2 sequences performed better than PET/CT in anatomical allocation of lesions (2.87?±?0.3 vs. 2.72?±?0.5; p?=?0.005). The quality of PET/CT images (2.97?±?0.2) was better than that of the respective PET scan of the PET/MR (2.69?±?0.5; p?=?0.007). Overall the maximum and mean lesional SUVs exhibited high correlations between PET/CT and PET/MR (ρ?=?0.87 and ρ?=?0.86, respectively; both p?<?0.001).

Conclusion

Despite a substantially later imaging time-point, the performance of simultaneous PET/MR was comparable to that of PET/CT in detecting lesions with increased [¹¹C]choline uptake in patients with prostate cancer. Anatomical allocation of lesions was better with simultaneous PET/MR than with PET/CT, especially in the bone and pelvis. These promising findings suggest that [¹¹C]choline PET/MR might have a diagnostic benefit compared to PET/CT in patients with prostate cancer, and now needs to be further evaluated in prospective trials.     

Anatomical and functional volume concordance between FDG PET,and T2 and diffusion-weighted MRI for cervical cancer: a hybrid PET/MR study

Purpose

To evaluate the concordance among ¹⁸F-FDG PET imaging, MR T2-weighted (T2-W) imaging and apparent diffusion coefficient (ADC) maps with diffusion-weighted (DW) imaging in cervical cancer using hybrid whole-body PET/MR.

Methods

This study prospectively included 35 patients with cervical cancer who underwent pretreatment ¹⁸F-FDG PET/MR imaging. ¹⁸F-FDG PET and MR images were fused using standard software. The percent of the maximum standardized uptake values (SUV_max) was used to contour tumours on PET images, and volumes were calculated automatically. Tumour volumes measured on T2-W and DW images were calculated with standard techniques of tumour area multiplied by the slice profile. Parametric statistics were used for data analysis.

Results

FDG PET tumour volumes calculated using SUV_max (14.30?±?4.70) and T2-W imaging volume (33.81?±?27.32 cm³) were similar (P?>?0.05) at 35 % and 40 % of SUV_max (32.91?±?18.90 cm³ and 27.56?±?17.19 cm³ respectively) and significantly correlated (P?<?0.001; r?=?0.735 and 0.766). The mean DW volume was 30.48?±?22.41 cm³. DW volumes were not significantly different from FDG PET volumes at either 35 % SUV_max or 40 % SUV_max or from T2-W imaging volumes (P?>?0.05). PET subvolumes with increasing SUV_max cut-off percentage showed an inverse change in mean ADC values on DW imaging (P?<?0.001, ANOVA).

Conclusion

Hybrid PET/MR showed strong volume concordance between FDG PET, and T2-W and DW imaging in cervical cancer. Cut-off at 35 % or 40 % of SUV_max is recommended for ¹⁸F-FDG PET/MR SUV-based tumour volume estimation. The linear tumour subvolume concordance between FDG PET and DW imaging demonstrates individual regional concordance of metabolic activity and cell density.     

Dual-time-point F-18 FDG PET/CT for evaluation in patients with malignant lymphoma

Objective

The aim of this study was to evaluate the usefulness of F-18 fluorodeoxyglucose (FDG) dual-time-point (DTP) positron emission tomography (PET)/computed tomography (CT) with semiquantitative analyses for the initial staging in patients with malignant lymphoma.

Methods

Forty-three patients had DTP PET/CT, with 60-min and 2-h scan [n?=?8, Hodgkin??s lymphoma (HL); n?=?12, indolent non-Hodgkin lymphoma (NHL); n?=?23, aggressive NHL].

Results

A total of 524 lesions were evaluated (406 lymph nodes and 118 extra-nodal lesions). The maximum standardized uptake value (SUV_max) on 2-h delayed scan (SUV₂) was significantly higher than those on 1-h early scan (SUV₁) for all groups (P?<?0.0001 for HL; P?<?0.0001 for indolent NHL; P?<?0.0001 for aggressive NHL). Significant differences were detected between HL and indolent NHL, between indolent NHL and the aggressive NHL for both SUV₁ and SUV₂ (each P?<?0.0001). No significant differences were detected between HL and aggressive NHL for both SUV₁ and SUV₂ (P?=?0.6891 for SUV₁; P?=?0.8828 for SUV₂); however, significant differences were detected for the retention index of SUV_max between these groups (P?=?0.0238).

Conclusions

DTP F-18 FDG PET/CT with a semiquantitative technique may have the potential to provide the more accurate diagnoses for the staging of malignant lymphoma and the more important role in predicting the histological grades of malignancy compared with single-time-point F-18 FDG-PET scan.     

68Ga-DOTA-TOC uptake in neuroendocrine tumour and healthy tissue: differentiation of physiological uptake and pathological processes in PET/CT

Purpose

We wanted to establish the range of ⁶⁸Ga-DOTA-TOC uptake in liver and bone metastases of patients with neuroendocrine tumours (NET) and to establish the range of its uptake in pancreatic NET. This would allow differentiation between physiological uptake and tumour-related somatostatin receptor expression in the pancreas (including the uncinate process), liver and bone. Finally, we wanted to test for differences in patients with NET, either treated or not treated with peptide receptor radionuclide therapy (PRRT).

Methods

In 249 patients, 390 ⁶⁸Ga-DOTA-TOC PET/CT studies were performed. The clinical indications for PET/CT were gastroenteropancreatic NET (194 studies), nongastroenteropancreatic NET (origin in the lung and rectum; 46 studies), NET of unknown primary (111 studies), phaeochromocytoma/glomus tumours (18 studies), and radioiodine-negative metastatic thyroid carcinoma (21 studies).

Results

SUV_max (mean ± standard deviation) values of ⁶⁸Ga-DOTA-TOC were 29.8?±?16.5 in 162 liver metastases, 19.8?±?18.8 in 89 bone metastases and 34.6?±?17.1 in 43 pancreatic NET (33.6?±?14.3 in 30 tumours of the uncinate process and 36.3?±?21.5 in 13 tumours of the pancreatic tail). A significant difference in SUV_max (p?<?0.02) was found in liver metastases of NET patients treated with PRRT. There were significant differences in SUV_max between nonmalignant and malignant tissue for both bone and liver metastases and for pancreatic NET including the uncinate process (p?<?0.0001). At a cut-off value of 17.1 the specificity and sensitivity of SUV_max for differentiating tumours in the uncinate process were 93.6 % and 90.0 %, respectively (p?<?0.0001).

Conclusion

⁶⁸Ga-DOTA-TOC is an excellent tracer for the imaging of tumours expressing somatostatin receptors on the tumour cell surface, facilitating the detection of even small tumour lesions. The noninvasive PET/CT approach by measurement of regional SUV_max can offer important clinical information to distinguish between physiological and pathological somatostatin receptor expression, especially in the uncinate process. PRRT does not significantly influence SUV_max, except in liver metastases of patients with NET.     

Dual-time-point [18F]-FDG PET/CT in the diagnostic evaluation of suspicious breast lesions

Purpose

The authors sought to evaluate whether the reacquisition of images 3 h after administration of radiotracer improves the sensitivity of fluorine-18 fluorodeoxyglucose positron emission tomography computed tomography ([¹⁸F]-FDG PET/CT) in patients with suspicious breast lesions.

Materials and methods

Forty-eight patients with 59 breast lesions underwent an [¹⁸F]-FDG PET/CT study in the prone position with a dual-time-point acquisition performed in the early phase 1 h after FDG administration (PET-1) and in the delayed phase 3 h after FDG administration (PET-2). Both examinations were evaluated qualitatively and semiquantitatively with calculation of the mean percentage variation of the standard uptake values (Δ% SUV_max) between PET-1 and PET-2. All lesions with an SUV_max ≥2.5 at PET-1 or a reduction in SUV between PET-1 and PET-2 were considered benign. The definitive histopathological diagnosis was available for all patients included in the study.

Results

The dual-time-point acquisition of [¹⁸F]-FDG PET/CT displayed an accuracy of 85% for lesions with an SUV_max ≥2.5 and/or positive Δ% SUV_max, with sensitivity and specificity values of 81% and 100% compared with 69%, 63% (both p<0.001) and 100% (p=n.s.), respectively, for the single-time-point acquisition. Malignant lesions showed an increase in FDG uptake between PET-1 and PET-2, with a Δ% SUV_max of 10±7 (p<0.04). In contrast, benign lesions showed a decrease in SUV between PET-1 and PET-2, with aΔ% SUV_max of ?21±7 (p<0.001).

Conclusions

The delayed repeat acquisition of PET images improves the accuracy of [¹⁸F]-FDG PET/CT in patients with suspicious breast lesions with respect to the single-time-point acquisition. In addition, malignant breast lesions displayed an increase in FDG uptake over time, whereas benign lesions showed a reduction. These variations in FDG uptake between PET-1 and PET-2 are a reliable parameter that can be used for differentiating between benign and malignant breast lesions.     

Comparison of PET/CT and PET/MRI hybrid systems using a 68Ga-labelled PSMA ligand for the diagnosis of recurrent prostate cancer: initial experience

Purpose

⁶⁸Ga-labelled HBED-CC-PSMA is a highly promising tracer for imaging recurrent prostate cancer (PCa). The intention of this study was to evaluate the feasibility of PET/MRI with this tracer.

Methods

Twenty patients underwent PET/CT 1 h after injection of the ⁶⁸Ga-PSMA ligand followed by PET/MRI 3 h after injection. Data from the two investigations were first analysed separately and then compared with respect to tumour detection rate and radiotracer uptake in various tissues. To evaluate the quantification accuracy of the PET/MRI system, differences in SUVs between PET/CT and corresponding PET/MRI were compared with differences in SUVs between PET/CT 1 h and 3 h after injection in another patient cohort. This cohort was investigated using the same PET/CT system.

Results

With PET/MRI, different diagnostic sequences, higher contrast of lesions and higher resolution of MRI enabled a subjectively easier evaluation of the images. In addition, four unclear findings on PET/CT could be clarified as characteristic of PCa metastases by PET/MRI. However, in PET images of the PET/MRI, a reduced signal was observed at the level of the kidneys (in 11 patients) and around the urinary bladder (in 15 patients). This led to reduced SUVs in six lesions. SUV_mean values provided by the PET/MRI system were different in muscles, blood pool, liver and spleen.

Conclusion

PCa was detected more easily and more accurately with Ga-PSMA PET/MRI than with PET/CT and with lower radiation exposure. Consequently, this new technique could clarify unclear findings on PET/CT. However, scatter correction was challenging when the specific ⁶⁸Ga-PSMA ligand was used. Moreover, direct comparison of SUVs from PET/CT and PET/MR needs to be conducted carefully.     

Correlation of measurements from diffusion weighted MR imaging and FDG PET/CT in GIST patients: ADC versus SUV

Purpose

We investigated the correlation relationship between ADCs measured by MRI and SUVs measured by PET/CT of lesions on GIST (gastrointestinal stromal tumor) patients to verify if MR is able to replace or serve as an alternative to PET/CT in GIST staging and treatment monitoring.

Materials and methods

Between September 2010 and January 2011, five patients with histologically proven metastatic GIST in Queen Mary Hospital, Hong Kong were enrolled into our study. All patients underwent both MRI and PET/CT scans at prognosis. Pearson's correlations of twenty-nine lesions were conducted between 5 pairs of ADCs and SUVs values.

Results

Lesions in the liver, peritoneum or bowel loops were found by PET/CT and no extra-abdominal lesion was identified. All twenty-nine lesions are identifiable by MRI with sensitivity of 100%. Significant inverse correlation were found between ADC_mean and SUV_mean (P = 0.006), ADC_mean and SUV_max (P = 0.010), ADC_min and SUV_max (P = 0.014), ADC_min and SUV_mean (P = 0.026), rADC_min and rSUV_max (P = 0.047).

Conclusion

DWI is comparable to PET/CT in visually detecting the GIST lesions’ location. Significant inverse correlations were found between ADCs from DWIBS and SUVs from PET/CT on data of GIST patients. This finding demonstrates that DWI is potentially capable of offering similar information for diagnosis and treatment response evaluating in GIST's patients as PET/CT does. Furthermore, ADC_min, which is determined by single pixel, is not as reliable as ADC_mean, which is weighted average value of the whole lesion volume.     

Use of diffusion-weighted imaging (DWI) in PET/MRI for head and neck cancer evaluation

Objective

The purpose of this study was to analyze whether diffusion-weighted imaging (DWI) adds significant information to positron emission tomography/magnetic resonance imaging (PET/MRI) on lesion detection and characterization in head and neck cancers.

Methods

Seventy patients with different head and neck cancers were enrolled in this prospective study. All patients underwent sequential contrast-enhanced (ce) PET/computed tomography (CT) and cePET/MRI using a tri-modality PET/CT-MR setup either for staging or re-staging. First, the DWI alone was evaluated, followed by the PET/MRI with conventional sequences, and in a third step, the PET/MRI with DWI was evaluated. McNemar’s test was used to evaluate differences in the accuracy of PET/MRI with and without DWI compared to the standard of reference.

Results

One hundred eighty-eight (188) lesions were found, and of those, 118 (62.8 %) were malignant and 70 (37.2 %) were benign. PET/MRI without DWI had a higher accuracy in detecting malignant lesions than DWI alone (86.8 % vs. 60.6 %, p?Conclusion The use of DWI as part of PET/MRI to evaluate head and neck cancers does not provide remarkable information. Thus, the use of DWI might not be needed in clinical PET/MRI protocols for the staging or restaging of head and neck cancers.     

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.     

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.     

Whole-body [18F]FDG PET/MRI vs. PET/CT in the assessment of bone lesions in oncological patients: initial results

Objectives

To compare [¹⁸?F]FDG PET/MRI with PET/CT for the assessment of bone lesions in oncologic patients.

Methods

This prospective study included 67 patients with solid tumours scheduled for PET/CT with [¹⁸?F]FDG who also underwent a whole-body PET/MRI scan. The datasets (PET/CT, PET/MRI) were rated by two readers regarding lesion conspicuity (four-point scale) and diagnostic confidence (five-point scale). Median scores were compared using the Wilcoxon test.

Results

Bone metastases were present in ten patients (15 %), and benign bone lesions in 15 patients (22 %). Bone metastases were predominantly localized in the pelvis (18 lesions, 38 %) and the spine (14 lesions, 29 %). Benign bone lesions were exclusively osteosclerotic and smaller than the metastases (mean size 6 mm vs. 23 mm). While PET/CT allowed identification of 45 of 48 bone metastases (94 %), PET/MRI allowed identification of all bone metastases (100 %). Conspicuity of metastases was high for both modalities with significantly better results using PET/MRI (p?<?0.05). Diagnostic confidence in lesion detection was high for both modalities without a significant difference. In benign lesions, conspicuity and diagnostic confidence were significantly higher with PET/CT (p?<?0.05).

Conclusions

[¹⁸?F]FDG PET/MRI shows high potential for the assessment of bone metastases by offering superior lesion conspicuity when compared to PET/CT. In hypersclerotic, benign bone lesions PET/CT still sets the reference.

Key Points

? PET/MRI and PET/CT are of equal value for the identification of disease-positive patients ? PET/MRI offers higher lesion conspicuity as well as diagnostic confidence ? PET/MRI is an attractive new alternative for the assessment of bone metastases     

PET/MRI in head and neck cancer: initial experience

Purpose

To evaluate the feasibility of PET/MRI (positron emission tomography/magnetic resonance imaging) with FDG (¹⁸F-fluorodeoxyglucose) for initial staging of head and neck cancer.

Methods

The study group comprised 20 patients (16 men, 4 women) aged between 52 and 81?years (median 64?years) with histologically proven squamous cell carcinoma of the head and neck region. The patients underwent a PET scan on a conventional scanner and a subsequent PET/MRI examination on a whole-body hybrid system. FDG was administered intravenously prior to the conventional PET scan (267?C395?MBq FDG, 348?MBq on average). The maximum standardized uptake values (SUV_max) of the tumour and of both cerebellar hemispheres were determined for both PET datasets. The numbers of lymph nodes with increased FDG uptake were compared between the two PET datasets.

Results

No MRI-induced artefacts where observed in the PET images. The tumour was detected by PET/MRI in 17 of the 20 patients, by PET in 16 and by MRI in 14. The PET/MRI examination yielded significantly higher SUV_max than the conventional PET scanner for both the tumour (p?<?0.0001) and the cerebellum (p?=?0.0009). The number of lymph nodes with increased FDG uptake detected using the PET dataset from the PET/MRI system was significantly higher the number detected by the stand-alone PET system (64 vs. 39, p?=?0.001).

Conclusion

The current study demonstrated that PET/MRI of the whole head and neck region is feasible with a whole-body PET/MRI system without impairment of PET or MR image quality.     

Preoperative PET/CT standardized FDG uptake values of pelvic lymph nodes as a significant prognostic factor in patients with endometrial cancer

Purpose

Using integrated PET/CT, we evaluated the prognostic relevance of preoperative pelvic lymph node (LN) ¹⁸F-FDG uptake in endometrioid endometrial cancer.

Methods

We retrospectively reviewed patients with pathologically proven endometrial cancer who underwent preoperative ¹⁸F-FDG PET/CT scans to evaluate the prognostic significance of PET/CT parameters and other clinicopathological variables. We used Cox proportional hazards regression to examine the relationship between recurrence and the maximum standardized uptake value (SUV_max) in pelvic LNs (SUV_LN) on FDG PET/CT.

Results

Clinical data, treatment modalities and results were reviewed in 70 eligible patients. The median postsurgical follow-up was 29 months (range 6 to 95 months). Receiver-operating characteristic analysis identified the significant SUV_LN cut-off value as 15. The SUV_LN correlated with FIGO stage (P?<?0.001), LN metastasis (P?<?0.001), lymphovascular space invasion (P?<?0.001), SUV_tumour (P?=?0.001), metastatic LN size (P?=?0.004), primary tumour size (P?=?0.012), tumour grade (P?=?0.015) and depth of tumour invasion (P?=?0.035). Regression analysis showed a statistically significant association between recurrence and SUV_LN (P?=?0.002). Recurrence differed significantly (P?<?0.001) between patients with SUV_LN >15 and those with SUV_LN ≤15.

Conclusion

Preoperative pelvic LN FDG uptake exhibited a strong significant association with recurrence of endometrioid endometrial cancer.