RPS 706 - Clinical utility of hybrid imaging with PET/CT/MRI

Purpose:

To elucidate the patterns of characteristic hypometabolism on 18F-FDG PET/CT in various subtypes of MSA and correlation with the patterns of uptake on Dopamine transporter imaging with 99mTc TRODAT-1 SPECT.

Methods and materials:

A retrospective analysis of 65 patients of clinically suspected MSA was done. All the subjects underwent 99mTc TRODAT-1 SPECT study and 18F-FDG PET/CT scan on two separate days, between 2013 and 2018. The scans were analysed both qualitatively (visually) and semi-quantitatively. The FDG uptake patterns were recorded, and areas of hypometabolism that were two standard deviations from the mean were considered abnormal.

Results:

All the subjects had an abnormal pattern of FDG uptake on PET scan, both on a visual inspection and semiquantitative analysis. In MSA-P subjects (n=22), diffuse predominant hypometabolism of the globus pallidus-putamen complex was noted with relative sparing of the caudate nuclei. In MSA-C subjects (n=23), characteristic hypometabolism was noted in the cerebellum and brainstem. In mixed subtypes (n=10), variable involvement of the basal ganglia, cerebellum, and brainstem was noted with frontoparietal hypometabolism. TRODAT scan was abnormal in all and showed pronounced asymmetry with prominent rostrocaudal gradient seen in the MSA-P subtype.

Conclusion:

Dopamine transporter imaging agent 99mTc TRODAT-1 SPECT not only helps in the confirmation of Parkinsonian disorders but also demonstrates varying patterns of distribution in different subtypes of MSA. Characteristic patterns of hypometabolism may help in the differentiation of the subtypes of MSA in the presence of clinically overlapping symptoms.

Limitations:

Retrospective design and semiquantitative assessment are the major limitations of this study.

Ethics committee approval

IRB approval was not required as it was a retrospective study.

Funding:

No funding was received for this work.

Purpose:

The aim was to evaluate the usefulness of ¹⁸F-choline (¹⁸F-FCH) PET-CT for parathyroid adenoma detection in patients with hyperparathyroidism in comparison with neck ultrasound (US) and parathyroid 99mTc-MIBI scintigraphy.

Methods and materials:

The 50 patients (45F/5M) underwent neck US, 99mTc- MIBI scintigraphy (subtractive and dual-phase planar and SPECT-CT imaging) and ¹⁸F-FCH PET-CT within 6 months. The findings were classified as positive, inconclusive or negative in terms of images typical for parathyroid adenoma in each imaging modality. The localisation of possible parathyroid adenoma in subsequent surgical operation was performed based on the ¹⁸F-FCH PET-CT images. The results were compared to the surgical and pathological findings and the follow-up evaluation. Additionally, laboratory tests were performed (plasma calcium and parathormone levels).

Results:

Primary hyperparathyroidism was diagnosed in 46/50 and secondary in 4/50 patients. The mean radioactivity of ¹⁸F-FCH was 215 MBq and the average time from radiotracer injection to scan was 67 minutes. 44 patients scanned with ¹⁸F-FCH PET-CT were classified as positive, 3 as inconclusive and 3 as negative. In the neck US results, 6 patients were scored as positive, 8 as inconclusive and 36 as negative. The results of 99mTc- MIBI scintigraphy were as follows: 8 patients positive, 4 inconclusive, 38 negative. Thirty-five patients underwent surgery, in 30 out of them (85,7%) surgical treatment was effective. Among 35 patients, 11 had previously undergone unsuccessful surgery (none of those patients had previously performed ¹⁸F-FCH PET-CT).

Conclusion:

The ¹⁸F-FCH PET-CT method demonstrates high accuracy in the detection of parathyroid adenomas compared to neck US and 99mTc-MIBI parathyroid scintigraphy, increasing the efficacy of surgical operation in patients with hyperparathyroidism.

Limitations:

Not all patients underwent surgery.

Ethics committee approval

The ethics committee approved this study.

Funding:

Purpose:

To investigate whether radiomic features computed on high b-value DWI sequences referring to tumour cellularity correlate with the ⁶⁸GA-PSMA PET/CT ligand, highly specific for the diagnosis of prostate cancer (PCa).

Methods and materials:

This study retrospectively enrols 17 patients belonging to a multi-cohort investigation for the clinical impact of 3T-mpMRI and ⁶⁸GA-PSMA PET/CT in PCa diagnosis and staging. PCa lesions were contoured in consensus by two experienced radiologists in either DWI or T2w sequences, depending on where they were more visible. 40% of SUV_max was used as the threshold to contour lesions on PET images and, on these regions, the median of the last decile of SUV (SUV_M90th) was computed. Instead, 84 radiomic features were computed on b-2000 DWI lesions and their value was correlated to SUV_M90th through the absolute Spearman index (ρ).

Results:

Several radiomic features showed excellent correlations with ⁶⁸GA-PSMA-SUV_M90th. In particular, the radiomic feature performing as the best is related to local tumour heterogeneity and showed ρ≥0.7 in 82% of patients, ρ≥0.5 in just two cases, and one-only patient yielded ρ=0.3.

Conclusion:

The outcome reveals a rank correlation between the degrees of PCa cellularity heterogeneity and ⁶⁸GA- PSMA -SUV_M90th. In other words, a wider expression of membrane receptors for PSMA seems corresponding to an over-proliferation of cells, which theoretically is suggestive of tumour onset and malignancy progression.

Limitations:

A wider cohort of patients is needed to better understand this correlation and to deepen the physiological and biomolecular causes of such behaviour.

Ethics committee approval

IRB approval, written informed consent was waived.

Funding:

No funding was received for this work.

Purpose:

EXPLORER is a new generation PET/CT scanner with unprecedented sensitivity and total-body coverage. Its clinical implementation changes the way PET/CT is interpreted and the radiologist needs to gain familiarity with the new way that the functional anatomy is seen. This work aims to characterise aspects of the impact of this new technology on the visualisation of small structures through a semiquantitative evaluation.

Methods and materials:

PET data from 19 subjects (healthy subjects, n=5, and oncology patients with limited disease, n=14) were acquired on the EXPLORER scanner for 20 min at 90-min post-injection of 18F-FDG. Data were reconstructed in 1-mm isotropic voxels using an OSEM iterative algorithm with 4 iterations and 20 subsets. At least 1-cm volumes of interest (VOIs) were placed on the liver (Lbkg), ascending aorta (AAbkg) and bone marrow at L3 vertebral body (L3), and smaller structures such as spinal cord (SC), adrenals (AG) and pituitary gland (PG). Semiquantitative values including the SUVmean, SUVmax and SUVpeak were recorded.

Results:

SUVmean values for larger structures were: Lbkg=2.5±0.70; AAbkg=1.61±0.39; L3=2.39±1.33. For smaller structures, SUVmax & peak were: for SC, 4.13±0.1.42 & 2.70±0.59 (varied by region); for PG, 5.54±1.60 & 3.26±0.88; and for AGs, 4.64±2.14 & 2.73±0.92. When PG and AG values were normalised for Lbkg, their ratios were: 2.4 & 1.9 for SUVmax and 1.4 & 1.1 for SUVpeak, respectively. No significant differences were seen between healthy and cancer patients.

Conclusion:

Initial EXPLORER scans in healthy and oncology subjects demonstrated that biodistribution values in small structures are higher than that usually seen from standard scanners. For example, the adrenals and pituitary gland uptake are higher than the liver background. This notion is critical to correctly interpret total-body PET/CT scans.

Limitations:

Small sample size.

Ethics committee approval

IRB#1498688-1 &1341792-4

Funding:

NIH R01 CA206187-01