The arterial input function: Spatial dependence within the imaging volume and its influence on 3D quantitative dynamic contrast-enhanced MRI for head and neck cancer.

PURPOSE: To evaluate the dependence of the arterial input function (AIF) on the imaging z-axis and its effect on 3D DCE MRI pharmacokinetic parameters as mediated by the SPGR signal equation and Extended Tofts-Kermode model. THEORY: For SPGR-based 3D DCE MRI acquisition of the head and neck, inflow effects within vessels violate the assumptions underlying the SPGR signal model. Errors in the SPGR-based AIF estimate propagate through the Extended Tofts-Kermode model to affect the output pharmacokinetic parameters. MATERIALS AND METHODS: 3D DCE-MRI data were acquired for six newly diagnosed HNC patients in a prospective single arm cohort study. AIF were selected within the carotid arteries at each z-axis location. A region of interest (ROI) was placed in normal paravertebral muscle and the Extended Tofts-Kermode model solved for each pixel within the ROI for each AIF. Results were compared to those obtained with a published population average AIF. RESULTS: Due to inflow effect, the AIF showed extreme variation in their temporal shapes. Ktrans was most sensitive to the initial bolus concentration and showed more variation over the muscle ROI with AIF taken from the upstream portion of the carotid. kep was less sensitive to the peak bolus concentration and showed less variation for AIF taken from the upstream portion of the carotid. CONCLUSION: Inflow effects may introduce an unknown bias to SPGR-based 3D DCE pharmacokinetic parameters. Variation in the computed parameters depends on the selected AIF location. In the context of high flow, measurements may be limited to relative rather than absolute quantitative parameters.

Radiology Performed Fluoroscopy-Guided Lumbar Punctures Decrease Volume of Diagnostic Study Interpretation - Impact on Resident Training and Potential Solutions.

OBJECTIVES: Lumbar punctures performed in radiology departments have significantly increased over the last few decades and are typically performed in academic centers by radiology trainees using fluoroscopy guidance. Performing fluoroscopy-guided lumbar punctures (FGLPs) can often constitute a large portion of a trainee's workday and the impact of performing FGLPs on the trainee's clinical productivity (i.e. dictating reports on neuroradiology cross-sectional imaging) has not been studied. The purpose of the study was to evaluate the relationship between the number of FGLPs performed and cross-sectional neuroimaging studies dictated by residents during their neuroradiology rotation (NR). MATERIAL AND METHODS: The number of FGLPs and myelograms performed and neuroimaging studies dictated by radiology residents on our neuroradiology service from July 2008 to December 2017 were retrospectively reviewed. The relationship between the number of FGLPs performed and neuroimaging studies (CT and MRI) dictated per day by residents was examined. RESULTS: Radiology residents (n = 84) performed 3437 FGLPs and myelograms and interpreted 33402 cross-sectional studies. Poisson regression demonstrated an exponential decrease in number of studies dictated daily with a rising number of FGLPs performed (P = 0.0001) and the following formula was derived: Number of expected studies dictated per day assuming no FGLPs × e-0.25 x number of FGLPs = adjusted expected studies dictated for the day. CONCLUSION: We quantified the impact performing FGLPs can have on the number of neuroimaging reports residents dictate on the NR. We described solutions to potentially decrease unnecessary FGLP referrals including establishing departmental guidelines for FGLP referrals and encouraging bedside lumbar punctures attempts before referral. We also emphasized equally distributing the FGLPs among trainees to mitigate procedural burden.