Predictors of Clopidogrel Hyper-Responsiveness in Neuro-Interventional Procedures.

BACKGROUND: Hyper-responsiveness to clopidogrel abnormally inhibits platelet aggregation and increases hemorrhagic complications. The present study investigated clinical factors related to clopidogrel hyper-responsiveness in neuro-interventional procedures. METHODS: Two hundred twenty-four patients receiving clopidogrel for coil embolization to treat unruptured cerebral aneurysm or carotid artery stenting to treat carotid artery stenosis at the internal carotid artery origin were retrospectively reviewed for their P2Y12 reactivity unit (PRU) values and clinical characteristics. Hyper-responsiveness to clopidogrel was defined as a PRU of <95. RESULTS: The mean PRU was 218.2 ± 77.8. Hyper-responsiveness to clopidogrel was observed in 12 patients (5.4%). Hyper-responsiveness was observed in younger patients, patients with a lower concentration of hemoglobin A1c, and patients with a higher low-density lipoprotein cholesterol (LDL-C) concentration compared with non-hyper-responsive patients (P = 0.01, P < 0.01, P < 0.01, respectively). On analysis of concomitant drugs, the patients in the hyper-responsive group were less frequently administered calcium channel blockers (CCBs) compared with the non-hyper-responsive group (P = 0.01). No significant differences in the usage of proton pump inhibitors or statins were observed. A LDL-C concentration of >120 mg/dL and no usage of CCBs were significant independent predictors of hyper-responsiveness to clopidogrel with a multivariate analysis (OR; 6.16, 95% CI, 1.57-26.64, P = 0.01, OR; 0.09, 95% CI, 0.01-0.82, P = 0.03, respectively). CONCLUSION: The present study shows that a higher LDL-C concentration and no usage of CCBs are independent predictors of clopidogrel hyper-responsiveness. These results are useful to predict perioperative hemorrhagic complications. Considering dose reduction of clopidogrel or alternative drugs in high risk cases is necessary to prevent perioperative hemorrhagic complications.

Eye-Lens Dose Reduction using Region of Interest (ROI) Attenuators in Neuroimaging.

Lens dose can be high during neuro-interventional procedures, increasing the risk of cataractogenesis. Although beam collimation can be effective in reducing lens dose, it also restricts the FOV. ROI imaging with a reduced-dose peripheral field permits full-field information with reduced lens dose. This work investigates the magnitude of lens-dose reduction possible with ROI imaging. EGSnrc Monte-Carlo calculations of lens dose were made for the Zubal head phantom as a function of gantry angulation and head shift from isocenter for both large and small FOV's. The lens dose for ROI attenuators of varying transmission was simulated as the weighted sum of the lens dose from the small ROI FOV and that from the attenuated larger FOV. Image intensity and quantum mottle differences between ROI and periphery can be equalized by image processing. The lens dose varies considerably with beam angle, head shift, and field size. For both eyes, the lens-dose reduction with an ROI attenuator increases with LAO angulation, being highest for lateral projections and lowest for PA. For an attenuator with small ROI field (5 × 5 cm) and 20% transmission, the lens dose for lateral projections is reduced by about 75% compared to a full dose 10 ×10 cm FOV, while the reduction ranges between 30 and 40% for PA projections. Use of ROI attenuators can substantially reduce the dose to the lens of the eye for all gantry angles and head shifts, while allowing peripheral information to be seen in a larger FOV.

Lens of the eye dose calculation for neuro-interventional procedures and CBCT scans of the head.

The aim of this work is to develop a method to calculate lens dose for fluoroscopically-guided neuro-interventional procedures and for CBCT scans of the head. EGSnrc Monte Carlo software is used to determine the dose to the lens of the eye for the projection geometry and exposure parameters used in these procedures. This information is provided by a digital CAN bus on the Toshiba Infinix C-Arm system which is saved in a log file by the real-time skin-dose tracking system (DTS) we previously developed. The x-ray beam spectra on this machine were simulated using BEAMnrc. These spectra were compared to those determined by SpekCalc and validated through measured percent-depth-dose (PDD) curves and half-value-layer (HVL) measurements. We simulated CBCT procedures in DOSXYZnrc for a CTDI head phantom and compared the surface dose distribution with that measured with Gafchromic film, and also for an SK150 head phantom and compared the lens dose with that measured with an ionization chamber. Both methods demonstrated good agreement. Organ dose calculated for a simulated neuro-interventional-procedure using DOSXYZnrc with the Zubal CT voxel phantom agreed within 10% with that calculated by PCXMC code for most organs. To calculate the lens dose in a neuro-interventional procedure, we developed a library of normalized lens dose values for different projection angles and kVp's. The total lens dose is then calculated by summing the values over all beam projections and can be included on the DTS report at the end of the procedure.