Assessing the effects of water exchange on quantitative dynamic contrast enhanced MRI

Abstract

Applying mathematical models to dynamic contrast enhanced MRI (DCE MRI) datato perform quantitative tracer kinetic analysis enables the estimation of tissue characteristics such as vascular permeability and the fractional volume of plasma in atissue. However, it is unclear to what extent modeling assumptions, particularly regarding water exchange between tissue compartments, impacts parameter estimatesderived from clinical DCE MRI data. In this work, a new model is developed whichincludes water exchange effects, termed the water exchange modified two compartment exchange model (WX-2CXM). Two boundaries of this model (the fast and noexchange limits) were used to analyse a clinical DCE MRI bladder cancer dataset.Comparisons with DCE CT, which is not affected by water exchange, suggested thatwater exchange may have affected estimates of vp , the fractional volume of plasma.Further investigation and simulations led to the development of a DCE MRI protocol which was sensitised to water exchange, in order to further evaluate the waterexchange effects found in the bladder cancer dataset. This protocol was tested byimaging the parotid glands in eight healthy volunteers, and confirmed evidence ofwater exchange effects on vp , as well as flow Fp and the fractional volume of extravascular extracellular space ve . This protocol also enabled preliminary estimatesof the water residence times in parotid tissue, however, these estimates had a largevariability and require further validation.The work presented in this thesis suggests that, although water exchange effects donot have a large effect on clinical data, the effect is measurable, and may lead tothe ability to estimate of tissue water residence times. Results do not support achange in the current practise of neglecting water exchange effects in clinical DCEMRI acquisitions.

Date of Award	1 Jan 1824
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Josephine Naish (Supervisor) & Stephen Williams (Supervisor)