Non-invasive assessment of stimulation-specific changes in cerebral glucose metabolism with functional PET.

PURPOSE: Functional positron emission tomography (fPET) with [18F]FDG allows quantification of stimulation-induced changes in glucose metabolism independent of neurovascular coupling. However, the gold standard for quantification requires invasive arterial blood sampling, limiting its widespread use. Here, we introduce a novel fPET method without the need for an input function. METHODS: We validated the approach using two datasets (DS). For DS1, 52 volunteers (23.2 ± 3.3 years, 24 females) performed Tetris® during a [18F]FDG fPET scan (bolus + constant infusion). For DS2, 18 participants (24.2 ± 4.3 years, 8 females) performed an eyes-open/finger tapping task (constant infusion). Task-specific changes in metabolism were assessed with the general linear model (GLM) and cerebral metabolic rate of glucose (CMRGlu) was quantified with the Patlak plot as reference. We then estimated simplified outcome parameters, including GLM beta values and percent signal change (%SC), and compared them, region and whole-brain-wise. RESULTS: We observed higher agreement with the reference for DS1 than DS2. Both DS resulted in strong correlations between regional task-specific beta estimates and CMRGlu (r = 0.763…0.912). %SC of beta values exhibited strong agreement with %SC of CMRGlu (r = 0.909…0.999). Average activation maps showed a high spatial similarity between CMRGlu and beta estimates (Dice = 0.870…0.979) as well as %SC (Dice = 0.932…0.997), respectively. CONCLUSION: The non-invasive method reliably estimates task-specific changes in glucose metabolism without blood sampling. This streamlines fPET, albeit with the trade-off of being unable to quantify baseline metabolism. The simplification enhances its applicability in research and clinical settings.

Assessment of the Size of the Surgical Site in Minimally Invasive Hip Surgery.

Objective: Minimally invasive approaches to the hip are beneficial to the patient, but reduce the space available for manipulation by the surgeon. Determining the available working space is important for the development of surgical instruments, to track movements during surgery, as well as to classify the invasiveness of the procedure. Approach: We evaluate three measurement methods to assess the volume of eight surgical sites in a cadaver study. The cavities were filled with an alginate cast to determine its dimensions. Second, the depth, height, and width of the surgical site were measured with a ruler and the volume was calculated. Last, the surface registration method was used to reconstruct the site. Results: We found that the mold filling method provides accurate results in determining the volume of a surgical site. The manual method using a ruler showed excellent reliability, but the calculations tended to overestimate the volume of the surgical site. In contrast, surface reconstruction tended to underestimate the volume of a surgical site, but the results closer resembled the ones derived from the mold filling method. Innovation: We presented a new method to assess the size of the surgical site intraoperatively in minimally invasive hip surgery. Conclusion: The manual method is reliable, but not as accurate as the surface reconstruction, while the mold filling method cannot be used in an intraoperative setup. Although surface reconstruction showed deficits regarding reliability, due to the lack of direct contact to the patient, it remains an appealing technique to measure the surgical site.