Multi-institutional Protocol Guidance for Pediatric Photon-counting CT.

Performing CT in children comes with unique challenges such as greater degrees of patient motion, smaller and densely packed anatomy, and potential risks of radiation exposure. The technical advancements of photon-counting detector (PCD) CT enable decreased radiation dose and noise, as well as increased spatial and contrast resolution across all ages, compared with conventional energy-integrating detector CT. It is therefore valuable to review the relevant technical aspects and principles specific to protocol development on the new PCD CT platform to realize the potential benefits for this population. The purpose of this article, based on multi-institutional clinical and research experience from pediatric radiologists and medical physicists, is to provide protocol guidance for use of PCD CT in the imaging of pediatric patients.

Neurologic immune-related adverse events associated with adjuvant ipilimumab: report of two cases.

BACKGROUND: PD-1 and CTLA-4 inhibitors are associated with several adverse events including a spectrum of immune-related adverse effects (irAEs). Neurologic irAEs are uncommon occurrences with varied presentations. We describe two separate cases of ipilimumab associated meningoencephalomyelitis and demyelinating polyneuropathy with unusual presentations. CASE PRESENTATION: Two melanoma patients were treated with ipilimumab in the adjuvant setting. The first patient developed a meningoencephalitis following 3 doses of ipilimumab. MRI imaging of the brain confirmed leptomeningeal enhancement although cerebrospinal fluid (CSF) analyses were negative for malignant cells consistent with meningoencephalomyelitis. Although she initially improved following treatment with steroids and intravenous immunoglobulin, she subsequently relapsed. She was successfully treated with infliximab and made a complete neurological recovery. A second patient developed progressive lower extremity weakness following two doses of ipilimumab. MRI imaging of the spine confirmed diffuse nerve root enhancement consistent with acute inflammatory demyelinating polyneuropathy (AIDP). He was treated with high dose steroids with resolution of neurological symptoms. Both patients remain disease free. CONCLUSIONS: Neurological irAEs are uncommon adverse events in the context of CTLA-4 and/or PD-1 inhibitor therapy. Care must be taken to distinguish these from leptomeningeal disease. Early recognition of neurological irAEs is critical for the initiation of specific anti-inflammatory agents to prevent and potentially reverse neurological sequelae.

A novel model of large vessel ischemic stroke in rabbits: microcatheter occlusion of the posterior cerebral artery.

BACKGROUND AND PURPOSE: The rabbit small clot embolic model for large vessel occlusion (LVO) is well established, yet has limitations. Blind introduction of autologous thrombus often fails to completely occlude a target vessel and, when successful, the precise timing of occlusion and revascularization is difficult to control. Studies of cellular biology and neuroimaging of acute reversible cerebral ischemia (ie, penumbral tissue) would benefit from a rabbit model in which LVO can be reliably induced, easily confirmed, and in which the time of occlusion and revascularization can be precisely controlled. METHODS: Transfemoral 1.5 F microcatheterization of the posterior cerebral artery (PCA) was performed in anesthetized rabbits (n=7) using fluoroscopic guidance. LVO with the wedged microcatheter was maintained for 30-210 min followed by reperfusion. Diffusion-weighted and T2 fluid-attenuated inversion recovery (FLAIR) MRI was performed 3 h after catheter removal on a 3 T scanner. Post-mortem histopathologic analysis of brain tissue was performed using triphenyltetrazolium chloride (TTC). RESULTS: Placing of the 1.5 F microcatheter tip in the PCA was successful in all seven animals. Infarct size on matched diffusion-weighted and TTC sections was strongly correlated (r(2)=0.86). Transient PCA occlusion of 30-60 min resulted in infarction of the ipsilateral hippocampus and thalamus, sparing the cortex, while more prolonged occlusion (180-210 min) resulted in cortical infarction as well. CONCLUSIONS: Image-guided microcatheter induction of PCA occlusion in rabbits can consistently produce time-dependent infarction of cortical and subcortical structures that is reliably detected by diffusion-weighted MRI, and thus may be a useful model for therapeutic studies in acute ischemic stroke.