The Peritoneum: What Nuclear Radiologists Need to Know.

The peritoneum is the largest and most complex serous membrane in the human body. The peritoneal membrane is composed of a layer of mesothelium supported by a thin layer of connective tissue. The peritoneum is one continuous sheet, forming two layers and a potential space between them - the peritoneal cavity- which is subdivided into multiple communicating spaces containing small amount of serous fluid that facilitates frictionless movement of mobile intraabdominal viscera. Peritoneum also contributes to fluid exchange mechanism and plays a role in immune response. The peritoneum is subject to many neoplastic and non-neoplastic processes including infections, trauma, developmental and inflammatory processes. Different Nuclear Medicine imaging techniques can be used to diagnose peritoneal diseases, most of these techniques can be customized depending on the clinical scenario and expected findings. Peritoneal scintigraphy can detect abnormal peritoneal communication or compartmentalization. Several nuclear medicine techniques can help characterize intraperitoneal fluid collections and differentiate sterile from infected fluid. PET imaging plays an important role in imaging of different neoplastic and non-neoplastic peritoneal pathologies. Nuclear radiologists need to be familiar with peritoneal anatomy and pathology to interpret peritoneal findings in dedicated peritoneal nuclear medicine imaging studies, as part of more general nuclear medicine scans, or on CT or MRI component of hybrid imaging studies. The purpose of this article is to review the normal peritoneal anatomy, various pathologic processes involving the peritoneum, and different nuclear medicine and hybrid imaging techniques that can help detect, characterize, and follow up peritoneal pathology.

The Role of the Cerebellum in Pain Perception: A Brain SPECT Perfusion Study in Patients with Burn Injuries.

BACKGROUND AND PURPOSE: Virtual reality (VR) is a promising tool for distraction analgesia. This study aims to compare brain perfusion patterns while patients were undergoing burn wound care in two conditions-VR distraction and control (NoVR). METHODS: With IRB approval, four patients hospitalized for acute burn care (three males and one female) participated in the study. All patients underwent wound care on two consecutive days; 1 day with standard analgesia and adjunctive VR, and the other day with standard analgesia alone, otherwise the wound care was very similar. Tc-99m ethyl cysteinate dimer was injected during wound care at the time of peak pain. Subjective patient reports on a 0-10 scale of pain intensity, time spent thinking about pain, and "fun" as well as opioid equivalent usage were analyzed. Voxel by voxel subtraction analysis of brain perfusion Single Photon Emission Computed Tomography (SPECT) images was performed at the group level. Statistical significance threshold was defined as P < .05. RESULTS: Mean group subjective scores (VR, NoVR, statistical significance, and P-value) were observed for maximal pain intensity (9.0, 8.8, insignificant, and P = .809), time spent thinking about pain (5.2, 10.0, significant, and P = .015), and fun (6.0, 2.5, significant, and P = .012). Subtraction group analysis demonstrated VR-induced modulation of brain activity with statistically significant relative suppression of cerebellar activation in the VR compared to intense cerebellar activation in the NoVR environments. CONCLUSION: Relative decrease in cerebellar perfusion based on stringent statistical threshold in the VR environment combined with improved subjective pain experience supports the hypotheses on the role of cerebellum in perception of noxious stimuli.

Virtual Reality to Relieve Pain in Burn Patients Undergoing Imaging and Treatment.

Pain from burn injuries is among the most excruciating encountered in clinical practice. Pharmacological methods often fail to achieve acceptable level of analgesia in these patients, especially during burn wound dressing and debridement. Virtual reality (VR) distraction is a promising analgesic technique that progressed significantly in the last decade with development of commercially available, low-cost, high-resolution, wide field-of-view, standalone VR devices that can be used in many clinical scenarios. VR has demonstrated clinical benefit as an adjunctive analgesic during burn wound dressing and other painful medical procedures. The technique has proven useful also in preparing patients for magnetic resonance imaging scans, particularly in claustrophobic patients. Modulation of pain-related brain activity at cortical and subcortical levels by VR, and its correlation with subjective improvement in various laboratory and clinical pain experiences has been demonstrated using multiple functional brain imaging studies including functional magnetic resonance imaging and brain perfusion single photon emission computed tomography.

Two signs indicative of successful access in nuclear medicine cerebrospinal fluid diversionary shunt studies.

BACKGROUND: Successful shunt access is the first step in a properly performed nuclear medicine cerebrospinal fluid (CSF) shunt study. OBJECTIVE: To determine the significance of the radiotracer configuration at the injection site during initial nuclear medicine CSF shunt imaging and the lack of early systemic radiotracer activity as predictors of successful shunt access. MATERIALS AND METHODS: With Institutional Review Board approval, three nuclear medicine physicians performed a retrospective review of all consecutive CSF shunt studies performed in children at our institution in 2015. Antecedent nuclear medicine CSF shunt studies in these patients were also assessed and included in the review. The appearance of the reservoir site immediately after radiotracer injection was classified as either figure-of-eight or round/ovoid configuration. The presence or absence of early systemic distribution of the tracer on the 5-min static images was noted and separately evaluated. RESULTS: A total of 98 nuclear medicine ventriculoperitoneal CSF shunt studies were evaluated. Figure-of-eight configuration was identified in 87% of studies and, when present, had 93% sensitivity, 78% specificity, 92% accuracy, 98% positive predictive value (PPV) and 54% negative predictive value (NPV) as a predictor of successful shunt access. Early systemic activity was absent in 89 of 98 studies. Lack of early systemic distribution of the radiotracer had 98% sensitivity, 78% specificity, 96% accuracy, 98% PPV and 78% NPV as a predictor of successful shunt access. Figure-of-eight configuration in conjunction with the absence of early systemic tracer activity had 99% PPV for successful shunt access. CONCLUSION: Figure-of-eight configuration at the injection site or lack of early systemic radiotracer activity had moderate specificity for successful shunt access. Specificity and PPV significantly improved when both signs were combined in assessment.

Optimization of Pediatric PET/CT.

PET/CT, the most common form of hybrid imaging, has transformed oncologic imaging and is increasingly being used for nononcologic applications as well. Performing PET/CT in children poses unique challenges. Not only are children more sensitive to the effects of radiation than adults but, following radiation exposure, children have a longer postexposure life expectancy in which to exhibit adverse radiation effects. Both the PET and CT components of the study contribute to the total patient radiation dose, which is one of the most important risks of the study in this population. Another risk in children, not typically encountered in adults, is potential neurotoxicity related to the frequent need for general anesthesia in this patient population. Optimizing pediatric PET/CT requires making improvements to both the PET and the CT components of the procedure while decreasing the potential for risk. This can be accomplished through judicious performance of imaging, the use of recommended pediatric 18fluorine-2-fluoro-2-deoxy-d-glucose (18F-FDG) administered activities, thoughtful selection of pediatric-specific CT imaging parameters, careful patient preparation, and use of appropriate patient immobilization. In this article, we will review a variety of strategies for radiation dose optimization in pediatric 18F-FDG-PET/CT focusing on these processes. Awareness of and careful selection of pediatric-specific CT imaging parameters designed for appropriate diagnostic, localization, or attenuation correction only CT, in conjunction with the use of recommended radiotracer administered activities, will help to ensure image quality while limiting patient radiation exposure. Patient preparation, an important determinant of image quality, is another focus of this review. Appropriate preparative measures are even more crucial in children in whom there is a higher incidence of brown fat, which can interfere with study interpretation. Finally, we will discuss measures to improve the patient experience, the resource use, the departmental workflow, and the diagnostic performance of the study through the use of appropriate technology, all in the context of minimizing procedure-related risks.

A Case of Nasal Merkel Cell Carcinoma Draining to a Buccinator Sentinel Lymph Node.

A 73-year-old man diagnosed with Merkel cell carcinoma of the left nasal ala was referred for preoperative scintigraphic sentinel lymph node mapping. In three separate foci around the lesion, 0.2 mCi of Tc-sulfur colloid was intradermally administered. Planar images demonstrated accumulation of tracer midway between the nose and left ear. SPECT/CT images localized radiotracer uptake to the left buccinator/buccal space, consistent with a buccinator lymph node, which is an inconsistent part of the facial lymphatic drainage. This case illustrates the added value of SPECT/CT and 3D reconstruction in sentinel lymph node localization, particularly in the head and neck.