Study DesignRetrospective review of an initial cohort of consecutive patients undergoing robot-assisted pedicle screw placement.PurposeWe aimed to evaluate the learning curve, if any, of this new technology over the course of our experience.Overview of LiteraturePercutaneous pedicle screws have specific advantages over open freehand screws. However, they require intraoperative imaging for their placement (e.g., fluoroscopy and navigation) and require increased surgeon training and skill with the learning curve estimated at approximately 20–30 cases. To our knowledge, this is the first study that measures the learning curve of robot-guided purely percutaneous pedicle screw placement with comprehensive objective postoperative computed tomography (CT) scoring, time per screw placement, and fluoroscopy time.MethodsWe included the first 80 consecutive patients undergoing robot-assisted spinal surgery at Melbourne Private Hospital. Data were collected for pedicle screw placement accuracy, placement time, fluoroscopy time, and revision rate. Patient demographic and relevant perioperative and procedural data were also collected. The patients were divided equally into four sub-groups as per their chronological date of surgery to evaluate how the learning curve affected screw placement outcomes.ResultsTotal 80 patients were included; 73 (91%) had complete data and postoperative CT imaging that could help assess that placement of 352 thoracolumbar pedicle screws. The rate of clinically acceptable screw placement was high (96.6%, 95.4%, 95.6%, and 90.7%, in groups 1 to 4, respectively, p=0.314) over time. The median time per screw was 7.0 minutes (6.5, 7.0, 6.0, and 6.0 minutes in groups 1 to 4, respectively, p=0.605). Intraoperative revision occurred in only 1 of the 352 screws (0.3%).Conclusions We found that robot-assisted screw placement had high accuracy, low placement time, low fluoroscopy time, and a low complication rate. However, there were no significant differences in these parameters at the initial experience and the practiced, experience placement (after approximately 1 year), indicating that robot-assisted pedicle screw placement has a very short (almost no) learning curve.

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Background Following reperfusion treatment in ischemic stroke, CT imaging at 24-hours is widely used to assess radiological outcomes. Even without visible hyperattenuation, occult angiographic contrast may persist in the brain and confound Hounsfield Unit-based imaging metrics such as Net Water Uptake (NWU). Aims We aimed to assess the presence and factors associated with retained contrast post-thrombectomy on 24-hour imaging using Dual Energy CT (DECT), and its impact on the accuracy of NWU as a measure of cerebral edema. Methods Consecutive patients with anterior circulation large vessel occlusion who had post-thrombectomy DECT performed 24-hours post-treatment from two thrombectomy stroke centers were retrospectively studied. NWU was calculated by interside comparison of Hounsfield Units of the infarct lesion and its mirror homolog. Retained contrast was quantified by the difference in NWU values with and without adjustment for iodine. Patients with visible hyperdensities from hemorrhagic transformation or visible contrast retention, and bilateral infarcts were excluded. Cerebral edema was measured by relative hemispheric volume (rHV) and midline shift (MLS). Results Of 125 patients analyzed (median age 71 [IQR 61-80], baseline NIHSS 16 [IQR 9.75-21]), reperfusion (defined as extended-Thrombolysis-In-Cerebral-Infarction 2b-3) was achieved in 113 patients (90.4%). Iodine-subtracted NWU was significantly higher than unadjusted NWU (17.1% vs 10.8%, p<0.001). In multivariable median regression analysis, increased age (p=0.024), number of passes (p=0.006), final infarct volume (p=0.023) and study site (p=0.021) were independently associated with amount of retained contrast. Iodine-subtracted NWU correlated with rHV (rho=0.154, p=0.043) and MLS (rho=0.165, p=0.033) but unadjusted NWU did not (rHV rho=-0.035, p=0.35; MLS rho=0.035, p=0.347). Conclusions Angiographic iodine contrast is retained in brain parenchyma 24-hours post-thrombectomy, even without visually obvious hyperdensities on CT, and significantly affects NWU measurements. Adjustment for retained iodine using DECT is required for accurate NWU measurements post-thrombectomy. Future quantitative studies analyzing CT after thrombectomy should consider occult contrast retention.

Introduction: CT performed 24h post-treatment is widely used to assess radiological outcomes in stroke studies. Even without visible hyperattenuation, occult angiographic contrast may persist in the brain and confound Hounsfield Unit-based imaging metrics such as Net Water Uptake (NWU), a measure of cerebral edema based on tissue hypoattenuation. We aimed to assess (1) the presence of retained contrast post-thrombectomy on 24h CT by comparing NWU measurements with and without adjustment for iodine using dual energy CT (DECT), (2) factors associated with amount of retention, and (3) its impact on the accuracy of NWU. Methods: In a prospective study of patients with anterior circulation large vessel occlusion who had post-thrombectomy follow-up DECT performed 24h post-treatment from two Comprehensive Stroke Centres (November 2021 to May 2022), NWU was calculated by interside comparison of Hounsfield Units of the infarct lesion and its mirror homolog. Retained contrast was quantified by the difference in NWU values with and without adjustment for iodine. We tested correlation between NWU and tissue swelling using relative hemispheric volume (rHV) and midline shift (MLS). Patients with visible hyperdensities from hemorrhagic transformation or visible contrast retention, and bilateral infarcts were excluded. Results: Of 125 patients analysed (median age 71 [IQR 61-80], baseline NIHSS 16 [IQR 9.75-21]), reperfusion (eTICI 2b-3) was achieved in 120 patients (96.8%). NWU measured with iodine adjustment was significantly higher than NWU measured without adjustment (17.1% vs 10.8%, p<0.001). In multivariable median regression analysis, age (p=0.031), number of passes (p<0.001) and having CT perfusion at baseline (p=0.008) were independently associated with amount of retained contrast. NWU measured with iodine adjustment correlated with rHV (p=0.043) and MLS (p=0.033), but NWU without adjustment did not (rHV p=0.350; MLS p=0.347). Conclusion: Occult angiographic iodine contrast significantly affects NWU on CT at 24h. Our data suggest adjustment for retained iodine using DECT is required for accurate NWU measures post-thrombectomy. Future studies analysing CT post-thrombectomy should consider the significance of occult contrast retention.

Background: Magnetic Resonance Imaging is used for evaluation of bone in Gaucher disease (GD), but a widely available quantitative scoring method remains elusive. Aims:The study purpose was to assess the reproducibility of the LiverLab tool for assessing bone marrow fat fraction (FF) and determine whether it could differentiate GD patients from healthy subjects.Methods: Ten healthy volunteers and 18 GD patients were prospectively recruited. FF was calculated at L3, L4 and L5. GD patient bone marrow burden (BMB) score assessed by one observer. Inter and intra-rater agreement assessed with Bland-Altman data plots. Differences in FF between healthy volunteers versus GD patients and between subjects treated versus not treated assessed using two-sample t-tests. In GD patients, the relationship between FF, BMB and glucosylsphingosine was determined using the Pearson's correlation coefficient.Results: Healthy volunteer mean FF was 0.36, standard deviation (SD) 0.10 (range 0.20-0.57). Intra and inter-rater SD were both 0.02. GD patient mean FF was 0.40, SD 0.13 (range 0.09-0.57). No statistical difference was shown between healthy volunteers and GD patients (P = 0.447) or between GD patients whether on enzyme replacement therapy or not (P = 0.090). No significant correlation between mean FF and total BMB (r = À0.525, P = 0.253) or between FF and glucosylsphingosine levels (r = 0.287, P = 0.248). Conclusion:Excellent reproducibility of LiverLab FF measurements across studies and observers is comparable to Dixon quantitative chemical shift imaging (QCSI). Lack of statistical difference between GD patients and controls may be explained by limited patient numbers, active treatment or mild disease severity in untreated patients.