Technical Note: Error metrics for estimating the accuracy of needle/instrument placement during transperineal MR/US-guided prostate interventions - Bonmati, E; Hu, Y; Villarini, B; Rodell, R; Martin, P; Han, L; Donaldson, I; Ahmed, HU; Moore, CM; Emberton, M; Barratt, DC (Medical Physics, 2018)