Novel contrast mixture achieves contrast resolution of human bladder wall suitable for T1 mapping: applications in interstitial cystitis and beyond.

Abstract

Instillation of novel contrast mixture (NCM) was recently shown to improve the contrast resolution of rat bladder wall with high contrast-to-noise ratio (CNR). Here, the clinical safety and the feasibility of NCM-enhanced MRI to achieve artifact-free visualization of human bladder wall suitable for quantitative measurement of the magnetic resonance (MR) longitudinal relaxation time (T1) was assessed. Six female subjects [two controls and two with Hunner-type interstitial cystitis ICand two with non-Hunner-type IC] consented for MRI at 3T before and after instillation of NCM [4mM gadobutrol and 5mM ferumoxytol in 50mL of sterile water for injection]. Single breath-hold fast MR acquisition in large readout bandwidth for 5-mm-thick single slice with variable flip angle was applied to minimize the motion and chemical shift artifacts in measurements of bladder wall thickness (BWT), CNR and T1 from 20 pixels. NCM instillation in subjects did not evoke pain or discomfort. Fourfold increase in bladder wall CNR (*p<0.02) and pixel size of 0.35mm with minimal influence of artifacts allowed accurate determination of bladder wall thinning~0.46mm from 50mL NCM (*p<0.05). Pre-contrast bladder wall T1 of 1544±34.2ms was shortened to 860.09±13.95ms in Hunner-type IC (*p<0.0001) relative to only 1257.42±20.59 and 1258.16±6.16ms in non-Hunner-type IC and controls, respectively. Findings demonstrate the safety and feasibility of NCM-enhanced MRI to achieve artifact-free differential contrast and spatial resolution of human bladder wall, which is suitable for measuring BWT and pixel-wise measurement of T1 in post-contrast setting.