Feasibility of low-dose CT protocols for evaluating the sinonasal cavity and reducing radiation exposure in dogs

© 2022 American College of Veterinary RadiologyWith the increasing use of radiation therapy for treatment of canine sinonasal neoplasia, there is a need for developing low-dose CT protocols to help minimize radiation exposure. The purpose of this study was to assess the trade-off between image quality and reduced radiation exposure of a low-dose CT technique in the canine sinonasal cavity. In this prospective, experimental study, CT images of the sinonasal cavities from 10 normal Beagles were acquired using high-dose (130 kVp) or low-dose (110 kVp, 80 kVp) protocol. Radiation dose and image quality were compared. Radiation exposure measured by the volume-weighted CT dose index and dose–length product was reduced by 36% at 110 kVp and 74% at 80 kVp respectively, compared to the corresponding values at 130 kVp (P = 0.000). Low-dose protocol resulted in higher image noise and reduced signal-to-noise ratio and contrast-to-noise ratio than 130 kVp in most evaluated regions of interest (P < 0.05). CT numbers of the contrast-enhanced structures were highest at 80 kVp (P = 0.000). Conspicuity of most sinonasal structures was similar for high dose and both lower dose protocols. The results of this study indicate that 80 or 110 kVp can be used for sinonasal CT examinations to reduce radiation exposure to the patient without compromising image quality.N

Quantification of renal T2 relaxation rate by use of blood oxygen level-dependent magnetic resonance imaging before and after furosemide administration in healthy Beagles

OBJECTIVE To assess the feasibility of blood oxygen level-dependent (BOLD) MRI for measurement of the renal T2* relaxation rate (R2*; proxy for renal oxygenation) before and after furosemide administration and to evaluate the reliability and repeatability of those measurements in healthy dogs. ANIMALS 8 healthy adult Beagles (4 males and 4 females). PROCEDURES Each dog was anesthetized and underwent BOLD MRI before (baseline) and 3 minutes after administration of furosemide (1 mg/kg, IV) twice, with a 1-week interval between scanning sessions. Mapping software was used to process MRI images and measure R2* and the difference in R2* (Delta R2*) before and after furosemide administration. The intraclass correlation coefficient was calculated to assess measurement reliability, and the coefficient of variation and Bland-Altman method were used to assess measurement repeatability. RESULTS Mean +/- SD baseline R2* in the renal medulla (24.5 +/- 3.8 seconds(-1)) was significantly greater than that in the renal cortex (20.6 +/- 2.7 seconds(-1)). Mean R2* in the renal cortex (18.6 +/- 2.6 seconds-1) and medulla (17.8 +/- 1.5 seconds(-1)) decreased significantly after furosemide administration. Mean Delta R2* in the medulla (6.7 +/- 2.4 seconds(-1)) was significantly greater than that in the renal cortex (2.1 +/- 0.7 seconds(-1)). All R2* and Delta R2* values had good or excellent reliability and repeatability, except the cortical Delta R2*, which had poor repeatability. CONCLUSIONS AND CLINICAL RELEVANCE Results suggested that BOLD MRI, when performed before and after furosemide administration, was noninvasive and highly reliable and repeatable for dynamic evaluation of renal oxygenation in healthy dogs.N