VERDICT‐AMICO: Ultrafast fitting algorithm for non‐invasive prostate microstructure characterization

Abstract

VERDICT (vascular, extracellular and restricted diffusion for cytometry in tumours) estimates and maps microstructural features of cancerous tissue non‐invasively using diffusion MRI. The main purpose of this study is to address the high computational time of microstructural model fitting for prostate diagnosis, while retaining utility in terms of tumour conspicuity and repeatability. In this work, we adapt the accelerated microstructure imaging via convex optimization (AMICO) framework to linearize the estimation of VERDICT parameters for the prostate gland. We compare the original non‐linear fitting of VERDICT with the linear fitting, quantifying accuracy with synthetic data, and computational time and reliability (performance and precision) in eight patients. We also assess the repeatability (scan‐rescan) of the parameters. Comparison of the original VERDICT fitting versus VERDICT‐AMICO showed that the linearized fitting (1) is more accurate in simulation for a signal‐to‐noise ratio of 20 dB; (2) reduces the processing time by three orders of magnitude, from 6.55 seconds/voxel to 1.78 milliseconds/voxel; (3) estimates parameters more precisely; (4) produces similar parametric maps and (5) produces similar estimated parameters with a high Pearson correlation between implementations, r 2 > 0.7. The VERDICT‐AMICO estimates also show high levels of repeatability. Finally, we demonstrate that VERDICT‐AMICO can estimate an extra diffusivity parameter without losing tumour conspicuity and retains the fitting advantages. VERDICT‐AMICO provides microstructural maps for prostate cancer characterization in seconds.

Magnetic resonance imaging of mean cell size in human breast tumors

“…It is therefore of interest to compare the accuracy and precision of different methods. The VERDICT approach attempts to map mean cell size in human tumors, but to date has been exclusively used in human prostate cancers . The VERDICT approach is different from IMPULSED in that though VERDICT also uses multiple diffusion times; it uses conventional PGSE sequences with higher b values.…”

“…Moreover, an optimization of experimental parameters could maintain the precision while minimizing scan time, such as utilized in our previous work using the Cramér‐Rao lower bound approach for optimizing T 1 and quantitative magnetization transfer protocols . Recent optimization efforts have shortened VERDICT acquisition time from 35 minutes to 12 minutes, suggesting that there is much room to accelerate the acquisition protocol of diffusion MRI‐based methods.…”

VERDICT MRI for Prostate Cancer: Intracellular Volume Fraction versus Apparent Diffusion Coefficient

“…VERDICT MRI maps (as shown in Fig 2 ) were generated by using the accelerated microstructure imaging via convex optimization, or AMICO, framework, which has previously been described by Bonet-Carne et al ( 9 ). The methods used for and results of extravascular extracellular volume fraction and vascular volume fraction analyses are presented in Appendix E1 (online).…”

Insights into tissue microstructure using a double diffusion encoding sequence on a clinical scanner: Validation and application to experimental tumor models

“…Models were written as dictionaries as in the Accelerated Microstructure Imaging via Convex Optimization (AMICO) framework . Signals were modeled using up to 3 compartments: an intracellular (ic), an extracellular (ec) and a vascular (va) compartment.…”

“…Models were written as dictionaries as in the Accelerated Microstructure Imaging via Convex Optimization (AMICO) framework. 43,44 Signals were modeled using up to compartments: an intracellular (ic), an extracellular (ec) and a vascular (va) compartment. The problem of estimating amplitudes (x) of dictionary entries from experimental data d (column vector) can be written as:…”