Olivier Rager

Detection and quantification of focal uptake in head and neck tumours: 18 F-FDG PET/MR versus PET/CT

PurposeOur objectives were to assess the quality of PET images and coregistered anatomic images obtained with PET/MR, to evaluate the detection of focal uptake and SUV, and to compare these findings with those of PET/CT in patients with head and neck tumours.MethodsThe study group comprised 32 consecutive patients with malignant head and neck tumours who underwent whole-body 18F-FDG PET/MR and PET/CT. PET images were reconstructed using the attenuation correction sequence for PET/MR and CT for PET/CT. Two experienced observers evaluated the anonymized data. They evaluated image and fusion quality, lesion conspicuity, anatomic location, number and size of categorized (benign versus assumed malignant) lesions with focal uptake. Region of interest (ROI) analysis was performed to determine SUVs of lesions and organs for both modalities. Statistical analysis considered data clustering due to multiple lesions per patient.ResultsPET/MR coregistration and image fusion was feasible in all patients. The analysis included 66 malignant lesions (tumours, metastatic lymph nodes and distant metastases), 136 benign lesions and 470 organ ROIs. There was no statistically significant difference between PET/MR and PET/CT regarding rating scores for image quality, fusion quality, lesion conspicuity or anatomic location, number of detected lesions and number of patients with and without malignant lesions. A high correlation was observed for SUVmean and SUVmax measured on PET/MR and PET/CT for malignant lesions, benign lesions and organs (ρ = 0.787 to 0.877, p < 0.001). SUVmean and SUVmax measured on PET/MR were significantly lower than on PET/CT for malignant tumours, metastatic neck nodes, benign lesions, bone marrow, and liver (p < 0.05). The main factor affecting the difference between SUVs in malignant lesions was tumour size (p < 0.01).ConclusionIn patients with head and neck tumours, PET/MR showed equivalent performance to PET/CT in terms of qualitative results. Comparison of SUVs revealed an excellent correlation for measurements on both modalities, but underestimation of SUVs measured on PET/MR as compared to PET/CT.

Diffusion-weighted and PET/MR Imaging after Radiation Therapy for Malignant Head and Neck Tumors.

Interpreting imaging studies of the irradiated neck constitutes a challenge because of radiation therapy-induced tissue alterations, the variable appearances of recurrent tumors, and functional and metabolic phenomena that mimic disease. Therefore, morphologic magnetic resonance (MR) imaging, diffusion-weighted (DW) imaging, positron emission tomography with computed tomography (PET/CT), and software fusion of PET and MR imaging data sets are increasingly used to facilitate diagnosis in clinical practice. Because MR imaging and PET often yield complementary information, PET/MR imaging holds promise to facilitate differentiation of tumor recurrence from radiation therapy-induced changes and complications. This review focuses on clinical applications of DW and PET/MR imaging in the irradiated neck and discusses the added value of multiparametric imaging to solve diagnostic dilemmas. Radiologists should understand key features of radiation therapy-induced tissue alterations and potential complications seen at DW and PET/MR imaging, including edema, fibrosis, scar tissue, soft-tissue necrosis, bone and cartilage necrosis, cranial nerve palsy, and radiation therapy-induced arteriosclerosis, brain necrosis, and thyroid disorders. DW and PET/MR imaging also play a complementary role in detection of residual and recurrent disease. Interpretation pitfalls due to technical, functional, and metabolic phenomena should be recognized and avoided. Familiarity with DW and PET/MR imaging features of expected findings, potential complications, and treatment failure after radiation therapy increases diagnostic confidence when interpreting images of the irradiated neck. Online supplemental material is available for this article.

Orbital tumours and tumour-like lesions: exploring the armamentarium of multiparametric imaging

AbstractAlthough the orbit is a small anatomical space, the wide range of structures present within it are often the site of origin of various tumours and tumour-like conditions, both in adults and children. Cross-sectional imaging is mandatory for the detection, characterization, and mapping of these lesions. This review focuses on multiparametric imaging of orbital tumours. Each tumour is reviewed in relation to its clinical presentation, compartmental location, imaging characteristics, and its histological features. We herein describe orbital tumours as lesions of the globe (retinoblastoma, uveal melanoma), optic nerve sheath complex (meningioma, optic nerve glioma), conal-intraconal compartment (hemangioma), extraconal compartment (dermoid/epidermoid, lacrimal gland tumours, lymphoma, rhabdomysarcoma), and bone and sinus compartment (fibrous dysplasia). Lesions without any typical compartmental localization and those with multi-compartment involvement (veno-lymphatic malformation, plexiform neurofibroma, idiopathic orbital pseudotumour, IgG4 related disease, metastases) are also reviewed. We discuss the role of advanced imaging techniques, such as MR diffusion-weighted imaging (DWI), diffusion tensor imaging, fluoro-2-deoxy-D-glucose positron emission tomography CT (FDG-PET CT), and positron emission tomography MRI (MRI PET) as problem-solving tools in the evaluation of those orbital masses that present with non-specific morphologic imaging findings. Main messages/Teaching points • A compartment-based approach is essential for the diagnosis of orbital tumours. • CT and MRI play a key role in the work-up of orbital tumours. • DWI, PET CT, and MRI PET are complementary tools to solve diagnostic dilemmas. • Awareness of salient imaging pearls and diagnostic pitfalls avoids interpretation errors.

PET/MR in Breast Cancer

Breast cancer is an international public health concern in which an optimal treatment plan requires a precise staging. Both MRI and PET imaging techniques have made significant progress in the last decades with constant improvements that made both modalities clinically relevant in several stages of breast cancer management and follow-up. On one hand, specific breast MRI permits high diagnostic accuracy for local tumor staging, and whole-body MRI can also be of great use in distant staging, eventually accompanied by organ-specific MRI sequences. Moreover, many different MRI sequences can be performed, including functional MRI, letting us foresee important improvements in breast cancer characterization in the future. On the contrary, (18)F-FDG-PET has a high diagnostic performance for the detection of distant metastases, and several other tracers currently under development may profoundly affect breast cancer management in the future with better determination of different types of breast cancers allowing personalized treatments. As a consequence PET/MR is a promising emerging technology, and it is foreseeable that in cases where both PET and MRI data are needed, a hybrid acquisition is justified when available. However, at this stage of deployment of such hybrid scanners in a clinical setting, more data are needed to demonstrate their added value beyond just patient comfort of having to undergo a single examination instead of two, and the higher confidence of diagnostic interpretation of these co-registered images. Optimized imaging protocols are still being developed and are prone to provide more efficient hybrid protocols with a potential improvement in diagnostic accuracy. More convincing studies with larger number of patients as well as cost-effectiveness studies are needed. This article provides insights into the current state-of-the-art of PET/MR in patients with breast cancer and gives an outlook on future developments of both imaging techniques and potential applications in the future.

SPECT/CT in differentiation of pseudarthrosis from other causes of back pain in lumbar spinal fusion: report on 10 consecutive cases.

Purpose: SPECT fused with computed tomography (CT) provides a new approach for more accurate diagnosis of pseudathrosis after spinal fusion procedures. The aim of this study was to compare the findings of SPECT fused with CT (SPECT/CT) with those of CT alone for the diagnosis of pseudarthrosis. Materials and Methods: SPECT and CT of 10 consecutive patients with recurrence of back and/or leg pain and with suspicion of pseudarthrosis on conventional radiologic imaging were analyzed retrospectively. All had previously undergone anterior and/or posterior lumbar fusion techniques. Presence of screw loosening, nonunion through or around the cages, and facet joint degeneration were assessed for diagnosis of pseudarthrosis. Based on SPECT/CT scan findings, the decision of surgical reintervention was made on 6 of 10 patients. The clinical follow-up (mean, 15.6 months; range, 5–29 months) was evaluated according to Macnab criteria (excellent, good, fair, poor). Results: All patients showing screw loosening on CT alone showed also an abnormal uptake on SPECT/CT. SPECT/CT did not show abnormal uptake in 3 of 5 patients who had nonunion through/around the cages on CT alone. SPECT/CT was able to show increased uptake in 6 cases in which CT alone did not show facet joint degeneration. Conclusions: In the lumbar spine, SPECT/CT seems to increase specificity for detection of nonunion of interbody devices compared with CT alone. It is more sensitive than CT to detect facet joint degeneration, and it can detect screw loosening as well as CT. These findings can be helpful for surgeons in planning appropriate surgical revision strategy.

Spinal uptake mimicking metastasis in SPECT/CT bone scan in a patient with superior vena cava obstruction.

A 46-year-old female patient with a mediastinal neuroendocrine carcinoma complicated by superior vena cava syndrome was referred for a bone metastatic workup. Bone scan with SPECT/CT showed several vertebral fixations without alterations on the unenhanced CT, but a CT scan with injection of contrast media showed vertebral densities matched to the lesions described on the SPECT/CT. This pattern confirmed presence of collateral paths through vertebral veins due to superior vena cava syndrome. Lack of metastases was confirmed by MRI.

Target Definition in Salvage Radiotherapy for Recurrent Prostate Cancer: The Role of Advanced Molecular Imaging

Salvage radiotherapy (SRT) represents the main treatment option for relapsing prostate cancer in patients after radical prostatectomy. Several open questions remain unanswered in terms of target volumes definition and delivered doses for SRT: the effective dose necessary to achieve biochemical control in the SRT setting may be different if the tumor recurrence is micro- or macroscopic. At the same time, irradiation of only the prostatic bed or of the whole pelvis will depend on the localization of the recurrence, local or locoregional. In the “theragnostic imaging” era, molecular imaging using positron emission tomography (PET) constitutes a useful tool for clinicians to define the site of the recurrence, the extent of disease, and individualize salvage treatments. The best option currently available in clinical routine is the combination of radiolabeled choline PET imaging and multiparametric magnetic resonance imaging (MRI), associating the nodal and distant metastases identification based on PET with the local assessment by MRI. A new generation of targeted tracers, namely, prostate-specific membrane antigen, show promising results, with a contrast superior to choline imaging and a higher detection rate even for low prostate-specific antigen levels; validation studies are ongoing. Finally, imaging targeting bone remodeling, using whole-body SPECT–CT, is a relevant complement to molecular/metabolic PET imaging when bone involvement is suspected.

Long-term Results of a Comparative PET/CT and PET/MRI Study of 11 C-Acetate and 18 F-Fluorocholine for Restaging of Early Recurrent Prostate Cancer

Purpose The aims of this study were to assess the intraindividual performance of 18F-fluorocholine (FCH) and 11C-acetate (ACE) PET studies for restaging of recurrent prostate cancer (PCa), to correlate PET findings with long-term clinical and imaging follow-up, and to evaluate the impact of PET results on patient management. Methods Thirty-three PCa patients relapsing after radical prostatectomy (n = 10, prostate-specific antigen [PSA] ⩽3 ng/mL), primary radiotherapy (n = 8, prostate-specific antigen ⩽5 ng/mL), or radical prostatectomy + salvage radiotherapy (n = 15) underwent ACE and FCH PET-CT (n = 29) or PET-MRI (n = 4) studies in a randomized sequence 0 to 21 days apart. Results The detection rate for ACE was 66% and for FCH was 60%. Results were concordant in 79% of the cases (26/33) and discordant in 21% (retroperitoneal, n = 5; pararectal, n = 1; and external iliac nodes, n = 1). After a median FU of 41 months (n = 32, 1 patient lost to FU), the site of relapse was correctly identified by ACE and FCH in 53% (17/32) and 47% (15/32) of the patients, respectively (2 M1a patients ACE+/FCH−), whereas in 6 of 32 patients the relapse was not localized. Treatment approach was changed in 11 (34.4%) of 32 patients and 9 (28%) of 32 patients restaged with ACE and FCH PET, respectively. Conclusions In early recurrent PCa, ACE and FCH showed minor discrepancies, limited to nodal staging and mainly in the retroperitoneal area, with true positivity of PET findings confirmed in half of the cases during FU. Treatment approach turned out to be influenced by ACE or FCH PET studies in one third of the patients.

Continuous bed motion Vs. step-and-shoot acquisition on clinical whole-body dynamic and parametric PET imaging

Continuous bed motion (CBM) has been recently introduced in the clinic as an alternative PET acquisition mode with respect to the traditional time-discretized step-and-shoot (SS) multi-bed acquisitions. In CBM mode, each slice can be considered as a different bed, since it is scanned over a different acquisition window. By reducing scan time discretization from a whole bed down to a single slice, the CBM acquisition offers additional degrees of freedom when designing acquisition protocols and thus larger margins for their optimization. Therefore, CBM mode could be particularly important for protocols of higher complexity, such as whole-body (WB) dynamic PET acquisitions. However, only a few studies have quantitatively validated the 2 modes on clinical data. In this work, we evaluate CBM vs. SS quantitative performance on a set of clinical data acquired over a 0-60min period using a WB dynamic PET acquisition protocol with a Biograph mCT TOF scanner. The TOF resolution (580ps) of the scanner allowed selecting faster CBM speeds (4.2mm/sec) and equivalent SS frames (30sec/bed), eventually permitting acquisition of 12 WB total passes of which half were performed in CBM mode and half in SS mode. The two modes were alternated between successive passes to allow a balanced interleaving of post-injection time between them to ensure an objective comparison. The evaluation of the 2 modes in terms of target-to-background (TBR) contrast and contrast-to-noise ratio (CNR) has been conducted for various noise levels by gradually adding all respective passes from each mode as well as in the parametric images after applying post-reconstruction WB Patlak analysis. Our results indicate a bias of ~10% between the 2 modes for the low count frames, reducing to <;3% as we gradually add all respective frames. In addition, a small bias of <;10% was observed in Patlak images at overlapped slices between beds, which is attributed to the non-uniformity of the axial sensitivity profile of SS mode.

High protracted 99mTc-HDP uptake in synthetic bone implants — A potentially misleading incidental finding on bone scintigraphy

We report the case of a 56-year-old male with bilateral total knee prostheses suffering from bilateral knee pain mainly on the right side and referred for bone scintigraphy. The medical history of the patient revealed an opening wedge high tibial osteotomy performed nine years earlier, with insertion of two blocks of ceramic made of hydroxyapatite and tricalcium phosphate in a wedge configuration as synthetic bone substitutes. The porous structure of these implants is analogous to the architecture of cancellous bone and permits fibrovascular and bone ingrowth, promoting the healing process. Planar scintigraphy and SPECT/CT showed an intense uptake within those implants in the early phase as well as in the late phase of the bone scan. It also showed bilateral patellofemoral arthritis. A (99m)Tc-labeled antigranulocyte antibody scintigraphy was negative for infection or inflammation. Bilateral patellar resurfacing led to complete symptom regression, confirmed at 10 months follow-up. To the best of our knowledge, this scintigraphic pattern with such a high tracer uptake reflecting bone substitute osteointegration has not yet been published. This should be considered in patients with such bone replacement materials that are increasingly used, in order to avoid false diagnosis of inflammation or infection.