Positron emission tomography/magnetic resonance imaging: the next generation of multimodality imaging?

Multimodal imaging is now well-established in routine clinical practice. Especially in the field of nuclear medicine, new positron emission tomography (PET) installations comprise almost exclusively combined PET/computed tomography (CT) scanners rather than PET-only systems. However, PET/CT has certain notable shortcomings, including the inability to perform simultaneous data acquisition and the significant radiation dose to the patient contributed by CT. Magnetic resonance imaging (MRI) offers, compared with CT, better contrast among soft tissues as well as functional-imaging capabilities. Therefore, the combination of PET with MRI provides many advantages that go far beyond simply combining functional PET information with structural MRI information. Many technical challenges, including possible interference between these modalities, have to be solved when combining PET and MRI, and various approaches have been adapted to resolving these issues. Here, we present an overview of current working prototypes of combined PET/MRI scanners from different groups. In addition, besides PET/MRI images of mice, the first such images of a rat acquired with the first commercial clinical PET/MRI scanner, are presented. The combination of PET and MRI is a promising tool in preclinical research and will certainly progress to clinical application.     

Imaging in multiple myeloma: Computed tomography or magnetic resonance imaging?

Multiple myeloma (MM) is the second most common type of hematological disease with its incidence rising in the elderly. In MM, the extent of the bone disease increases both morbidity and mortality. The detection of lytic bone lesions on imaging, especially computerized tomography (CT) and magnetic resonance imaging (MRI) is crucial to separate asymptomatic from symptomatic MM patients even when no clinical symptoms are present. Although radiology is essential in the staging and management of patients with MM there is still high variability in the choice between MRI and CT. In addition, there is still suboptimal agreement among readers. The potential of medical imaging in MM is largely under-evaluated: artificial intelligence, radiomics and new quantitative methods to report CT and MRI will improve imaging usage.     

FDG positron emission tomography/computed tomography studies of Wilms’ tumor

Purpose  

The purpose of this analysis was to evaluate the utility of FDG PET/CT scanning in patients with Wilms’ tumors.     

FDG positron emission tomography in head and neck cancer: pitfall or pathology?

PURPOSE: Fluorodeoxyglucose (FDG) positron emission tomography (PET) is a functional imaging technique used for imaging and staging malignant diseases. In many oncologic situations, however, abnormal changes seen on the PET studies are not caused by tumor, which is especially true in the head and neck region. The authors present an overview of the phenomena that may confound the interpretation of the images in head and neck cancer. MATERIALS AND METHODS: FDG PET studies were performed in patients with primary head and neck cancer and in patients in whom recurrent disease was likely. The results were correlated with clinical findings. Eight solitary cases were selected from a total of 180 patients studied. RESULTS AND CONCLUSIONS: Benign lesions and iatrogenic and physiologic changes may show increased FDG uptake. Therefore, clinical information on previous surgical interventions and optimal patient preparation are necessary for adequate interpretation. If these prerequisites can be met, benign lesions appear to be the only lesions that may interfere with the specificity of FDG PET.     

Is hybridic positron emission tomography/computerized tomography the only option? The future of nuclear medicine and molecular imaging

As we all know, Nuclear Medicine is the medical science using nuclear radiation for diagnosis, treatment and research. Nuclear Medicine, in contrast to Radiology, makes use of unsealed sources of radiation. Nuclear Medicine a few years ago has partly offered Nuclear Cardiology, the most lucrative of all Nuclear Medicine "children" at that time, to Cardiology. Radiology, has succeeded in being recognized by the European Union Authorities as Clinical Radiology. The word "clinical" offers greater independence to Clinical Radiology and makes it difficult for such a specialty to relinquish any of its equipment i.e. the diagnostic CT scan or the newly developed fast angiography CT, to other specialties. Contrary to Clinical Radiology, Nuclear Medicine being a laboratory specialty in most countries seems to have no right to deny offering, after some period of "proper certified education", its PET camera to Clinical Radiologists. Nuclear Medicine by virtue of its unique diagnostic techniques and treatments, is and should be recognized as a "Clinical Specialty" The interference of other specialties in the fields of Nuclear Medicine is also indicated by the fact that in vitro techniques of Nuclear Medicine are often used by Endocrinologists and Oncologists in their own laboratories. Also in some hospitals the Director of the Radiology Department acts as the Director of Nuclear Medicine Laboratory. Finally at present, Radiologists wish after "proper certified education", to be on equal terms in charge of the new hybridic equipment, the PET/CT scanner. If that is followed to happen, Nuclear Medicine will be in a difficult position losing at least part of PET and consequently should ask for help from its "Overlords and Protectors" i.e. the National and the European Societies of Nuclear Medicine and the Society of Nuclear Medicine of the United States of America. Radiology as a specialty participating om equal terms with the PET camera will then include the study of: a) "open sources of radiation" b) nuclear radiation and c) molecular nuclear medicine. The "European Journal of Nuclear Medicine and Molecular Imaging" shall have to erase the three last words of its title and be renamed. As Professor Abass Alavi et al (2007), have mentioned: "Is PET/CT the only option?" In favor of PET/CT are the following: Attenuation correction (AC) and better anatomical localization of lesions visualized with PET. Also PET/CT can be used as a diagnostic CT scanner (dCT). Against using the PET/CT scanners are the following arguments: a) This equipment is not necessary because we can always ask the Radiologists for a dCT scan. Many patients have already done a dCT scan at the time they are referred for a PET scan to the Nuclear Medicine Department. b) The absolute clinical indications for PET/CT with the use of a contrast agent, are under investigation. c) Although there is at present a list of indications suggested for the PET/CT scanner, there are studies disputing some of these indications, as for example in metastatic colon cancer where a high diagnostic accuracy for PET study alone, has been reported. d) The option of AC performed by the PET/CT scanner has also been questioned. Artifacts may be up to 84%. e) The PET/CT is expensive, time consuming, space occupying, and needs additional medical and technical personnel. f) Not to mention the extra radiation dose to the patients. g) Shall we inform those young medical students who wish to become nuclear medicine physicians, to hold their decision till the content of future Nuclear Medicine is clarified? We may suggest that: Our specialty could be renamed as: "Clinical Nuclear Medicine" and include additional "proper certified education" on the PET/CT equipment. The PET/CT scanner should remain in the Nuclear Medicine Department where Radiologists could act as advisors.     

Muscular involvement of Behçet's disease: ultrasonography, computed tomography, and magnetic resonance imaging findings

Behçet's disease (BD) is a form of systemic vasculitis with the classic triad of recurrent oral and genital ulcers along with uveitis. In BD, muscular involvement is very rare. We report a case of muscular involvement in BD with characteristic findings using ultrasonography, computed tomography, and magnetic resonance imaging.     

Diagnosis of pulmonary infarction in post-mortem computed tomography and post-mortem magnetic resonance imaging—a technical note

International Journal of Legal Medicine - Pulmonary thromboembolism may be accompanied by pulmonary infarction. Even though pulmonary thromboembolism (PTE) is a frequently found cause of death at...     

Vacuum phenomenon: prevalence and appearance in the knee with 3 T magnetic resonance imaging

Objectives  

To determine the prevalence of vacuum phenomenon (VP) in the knee on magnetic resonance (MR) images, describe the imaging features that characterize VP, and assess how often VP mimics pathological knee lesions.     

Tumor lesion detection: when is integrated positron emission tomography/computed tomography more accurate than side-by-side interpretation of positron emission tomography and computed tomography?

OBJECTIVES: To determine if there is added value to oncology studies performed with a dedicated in-line positron emission tomography (PET)/computed tomography (CT) scanner as compared with PET read side by side with diagnostic CT (DCT). METHODS: Forty-one consecutive oncology patients referred for PET/CT who had contemporary DCT scans for review were enrolled. Body regions assessed on a DCT scan were assessed on PET/CT and by side-by-side reading of PET and DCT (SBS PET/DCT). Lesions identified on DCT, the CT portion of PET/CT, SBS PET/DCT, and the reading of fused PET/CT images were scored as benign or malignant. The PET portion of the PET/CT study was read by 2 teams: the first read the SBS PET/DCT scan and the other read the complete fused PET/CT scan. For discordant lesions, the final diagnosis was determined by pathologic findings (n = 6) or imaging follow-up (n = 21). RESULTS: Twenty-seven (16.1%) of the 168 lesions were discordant when comparing analysis of fused PET/CT and SBS PET/DCT. Sixteen (9.5%) were fundamentally discordant, and 11(6.6%) were discordant in degree of confidence. For all discordant lesions only, the sensitivity, specificity, negative predictive value, positive predictive value, and accuracy for PET/CT were 100%, 33%, 100%, 94%, and 78%, respectively, and for SBS PET/DCT, they were 38%, 50%, 19%, 73%, and 30%, respectively (P < 0.001 for sensitivity, P = not specific for specificity). The 2 main causes for misclassification on SBS PET/DCT were incorrect localization (n = 12) and changes occurring in the time gap between DCT and PET/CT (n = 4). CONCLUSIONS: In-line PET/CT offers better lesion localization in comparison to the visual fusion of PET and CT, especially for small lymph nodes, lesions adjacent to mobile organs, or lesions adjacent to the chest or abdominal wall.     

Can dynamic susceptibility contrast magnetic resonance imaging replace single-photon emission computed tomography in the diagnosis of patients with Alzheimer's disease? A pilot study

Purpose: To compare single-photon emission computed tomography (SPECT) and magnetic resonance imaging (MRI) in a cohort of patients examined for suspected dementia, including patients with no objective cognitive impairment (control group), mild cognitive impairment (MCI), and Alzheimer's disease (AD).

Material and Methods: Twenty-four patients, eight with AD, 10 with MCI, and six controls were investigated with SPECT using ^99mTc-hexamethylpropyleneamine oxime (HMPAO) and dynamic susceptibility contrast magnetic resonance imaging (DSC-MRI) with gadobutrol. Three observers performed a visual interpretation of the SPECT and MR images using a four-point visual scale.

Results: SPECT was superior to DSC-MRI in differentiating normal from pathological. All three observers showed statistically significant results in discriminating between the control group, AD, and MCI by SPECT, with a P value of 0.0006, 0.04, and 0.01 for each observer. The statistical results were not significant for MR (P values 0.8, 0.1, and 0.2, respectively).

Conclusion: DSC-MRI could not replace SPECT in the diagnosis of patients with Alzheimer's disease. Several patient- and method-related improvements should be made before this method can be recommended for clinical practice.     

Simultaneous in vivo magnetic resonance imaging and radioactive measurements with the β-MicroProbe

Purpose Multimodal instrumentation is a new technical approach allowing simultaneous and complementary in vivo recordings of complementary biological parameters. To elucidate further the physiopathological mechanisms in intact small animal models, especially for brain studies, a challenging issue is the actual coupling of magnetic resonance imaging (MRI) techniques with positron emission tomography (PET): it has been shown that running the technology for radioactive imaging in a magnet alters the spatiotemporal performance of both modalities. Thus, we propose an alternative coupling of techniques that uses the β-MicroProbe instead of PET for local measurements of radioactivity coupled with MRI. Methods We simultaneously recorded local radioactivity due to [¹⁸F]MPPF (a 5-HT_1A receptor PET radiotracer) binding in the hippocampus with the β-MicroProbe and carried out anatomical MRI in the same anaesthetised rat. Results The comparison of [¹⁸F]MPPF kinetics obtained from animals in a magnet with kinetics from a control group outside the magnet allowed us to determine the stability of tracer biokinetic measurements over time in the magnet. We were thus able to show that the β-MicroProbe reliably measures radioactivity in rat brains under an intense magnetic field of 7 Tesla. Conclusion The biological validation of a β-MicroProbe/MRI dual system reported here opens up a wide range of future multimodal approaches for functional and pharmacological measurements by the probe combined with various magnetic resonance technologies, including anatomical MRI, functional MRI and MR spectroscopy.     

Synthesis and biological evaluation of two agents for imaging estrogen receptor β by positron emission tomography: challenges in PET imaging of a low abundance target

IntroductionIndependent measurement of the levels of both the estrogen receptors, ERα and ERβ, in breast cancer could improve prediction of benefit from endocrine therapies. While ERα levels can be measured by positron emission tomography (PET) using 16α-[¹⁸F]fluoroestradiol (FES), no effective agent for imaging ERβ by PET has yet been reported.MethodsWe have prepared the fluorine-18 labeled form of 8β-(2-fluoroethyl)estradiol (8BFEE₂), an analog of an ERβ-selective steroidal estrogen, 8β-vinylestradiol; efficient incorporation of fluorine-18 was achieved, but required very vigorous conditions. We have examined the biodistribution of this compound, as well as of Br-041, an analog of a known non-steroidal ERβ-selective ligand (ERB-041), labeled with bromine-76. Studies were done in immature female rodents, with various pharmacological and endocrine perturbations to assess ERβ selectivity of uptake.ResultsLittle evidence of ERβ-mediated uptake was observed with either [¹⁸F]8BFEE₂ or [⁷⁶Br]Br-041. Attempts to increase the ERβ content of target tissues were not effective and failed to improve biodistribution selectivity.ConclusionsBecause on an absolute basis level, ERβ levels are low in all target tissues, these studies have highlighted the need to develop improved in vivo models for evaluating ERβ-selective radiopharmaceuticals for use in PET imaging. Genetically engineered breast cancer cells that are being developed to express either ERα or ERβ in a regulated manner, grown as xenografts in immune-compromised mice, could prove useful for future studies to develop ER subtype-selective radiopharmaceuticals.     

Oncocytic carcinoid tumor of the lung with intense F-18 fluorodeoxyglucose (FDG) uptake in positron emission tomography–computed tomography (PET/CT)

The present report describes a case of typical carcinoid tumor with intense fluorodeoxyglucose (FDG) uptake. The most of tumor cells were characterized by eosinophilic cytoplasm resulting from accumulation of mitochondria, which was called an oncocytic carcinoid tumor. Glucose transporter type 1 (GLUT-1) was expressed in a membranous pattern in the oncocytic component. Oncocytic carcinoid tumors could show intense FDG uptake due to the numerous intracellular mitochondria and the membranous overexpression of GLUT-1. Thus, it could be a potential pitfall of interpreting FDG-PET/CT image.     

Can magnetic resonance imaging predict the success of parturition in oxytocin-induced pregnant women?

The aim of this study was to assess whether magnetic resonance imaging could predict the outcome of attempted vaginal delivery in a group of pregnant women whose parturition had to be induced by oxytocin. The signal intensity and morphology alterations in the cervix of 21 full-term pregnant women were analyzed before the induction of parturition. T2-weighted gradient echo sequences were utilized and signal intensity in the cervix was measured from the anterior and posterior lips of the cervix. An index indicating the brightness range of the cervix was formulated to overcome the effects of the individual intensity changes. Imaging features including the signal intensity and the evidence of effacement were correlated with the actual type of delivery performed. Images were also assessed visually by two independent radiologists. Statistical analysis of brightness indexes that were considered to have a predictive value as an indicator for possible delivery was not significant. However, visually assessed signal intensity of the cervix correlated strongly with the type of delivery. Effacement itself was the most reliable parameter in predicting the progress of the delivery. In conclusion, MR imaging seems to be useful for predicting normal parturition in full-term pregnant women who need oxytocin induction. However, the presence of effacement seems to be a more reliable and practical parameter that will be preferred in that prediction. Received: 21 October 1998; Revised: 19 April 1999; Accepted: 21 October 1999     

F-18 FDG positron emission tomographic imaging in a case of ruptured breast implant: inflammation or recurrent tumor?

F-18 fluorodeoxyglucose (FDG) positron emission tomography (PET) has proved clinically useful for both malignant and inflammatory lesions. The author describes a 54-year-old woman with previously treated carcinoma of the breast. There was spontaneous rupture of a breast implant placed previously as part of a reconstruction. While being evaluated clinically, prominent axillary lymph nodes were palpated on the ipsilateral side of the recent implant rupture. An F-18 FDG PET scan demonstrated intense uptake in these nodes. Lymph node biopsy demonstrated benign inflammatory reaction and no recurrence of malignancy.     

Clinical application of bilateral high temporal and spatial resolution dynamic contrast-enhanced magnetic resonance imaging of the breast at 7 T

Objective

The objective of our study was to evaluate the clinical application of bilateral high spatial and temporal resolution dynamic contrast-enhanced magnetic resonance imaging (HR DCE-MRI) of the breast at 7 T.

Methods

Following institutional review board approval 23 patients with a breast lesion (BIRADS 0, 4–5) were included in our prospective study. All patients underwent bilateral HR DCE-MRI of the breast at 7 T (spatial resolution of 0.7 mm³ voxel size, temporal resolution of 14 s). Two experienced readers (r1, r2) and one less experienced reader (r3) independently assessed lesions according to BI-RADS®. Image quality, lesion conspicuity and artefacts were graded from 1 to 5. Sensitivity, specificity and diagnostic accuracy were assessed using histopathology as the standard of reference.

Results

HR DCE-MRI at 7 T revealed 29 lesions in 23 patients (sensitivity 100 % (19/19); specificity of 90 % (9/10)) resulting in a diagnostic accuracy of 96.6 % (28/29) with an AUC of 0.95. Overall image quality was excellent in the majority of cases (27/29) and examinations were not hampered by artefacts. There was excellent inter-reader agreement for diagnosis and image quality parameters (κ?=?0.89–1).

Conclusion

Bilateral HR DCE-MRI of the breast at 7 T is feasible with excellent image quality in clinical practice and allows accurate breast cancer diagnosis.

Key points

? Dynamic contrast-enhanced 7-T MRI is being developed in several centres. ? Bilateral high resolution DCE-MRI of the breast at 7 T is clinically applicable. ? 7-T HR DCE-MRI of the breast provides excellent image quality. ? 7-T HR DCE-MRI should detect breast cancer with high diagnostic accuracy.     

Is contrast material needed after treatment of malignant lymphoma in positron emission tomography/computed tomography?

Purpose  

Positron emission tomography (PET)/computed tomography (CT) with ¹⁸F-fluorodeoxyglucose is widely used for post-therapeutic surveillance of malignant lymphoma. Debate still exists as to whether intravenous contrast media during the CT stage of a PET/CT scan should be used. The purpose of this study was to investigate the clinical value of contrast agent in PET/CT in patients with lymphoma following treatment.     

Role of magnetic resonance imaging in entrapment and compressive neuropathy—what, where, and how to see the peripheral nerves on the musculoskeletal magnetic resonance image: part 2. Upper extremity

The diagnosis of nerve entrapment and compressive neuropathy has been traditionally based on the clinical and electrodiagnostic examinations. As a result of improvements in the magnetic resonance (MR) imaging modality, it plays not only a fundamental role in the detection of space-occupying lesions, but also a compensatory role in clinically and electrodiagnostically inconclusive cases. Although ultrasound has undergone further development in the past decades and shows high resolution capabilities, it has inherent limitations due to its operator dependency. We review the course of normal peripheral nerves, as well as various clinical demonstrations and pathological features of compressed and entrapped nerves in the upper extremities on MR imaging, according to the nerves involved. The common sites of nerve entrapment of the upper extremity are as follows: the brachial plexus of the thoracic outlet; axillary nerve of the quadrilateral space; radial nerve of the radial tunnel; ulnar nerve of the cubital tunnel and Guyon’s canal; median nerve of the pronator syndrome, anterior interosseous nerve syndrome, and carpal tunnel syndrome. Although MR imaging can depict the peripheral nerves in the extremities effectively, radiologists should be familiar with nerve pathways, common sites of nerve compression, and common space-occupying lesions resulting in nerve compression in MR imaging.