Clinical quantitative MRI and the need for metrology

Abstract

MRI has been an essential diagnostic tool in healthcare for several decades. It offers unique insights into most tissues without the need for ionising radiation. Historically, MRI has been predominantly used qualitatively, images are formed to allow visual discrimination of tissues types and pathologies, rather than providing quantitative measurements. Increasingly, quantitative MRI (qMRI) is also finding clinical application, where images provide the basis for physical measurements of, e.g. tissue volume measures and represent aspects of tissue composition and microstructure. This article reviews some common current research and clinical applications of qMRI from the perspective of measurement science. qMRI not only offers additional information for radiologists, but also the opportunity for improved harmonisation and calibration between scanners and as such it is well-suited to large-scale investigations such as clinical trials and longitudinal studies. Realising these benefits, however, presents a new kind of technical challenge to MRI practioners. When measuring a parameter quantitatively, it is crucial that the reliability and reproducibility of the technique are well understood. Strictly speaking, a numerical result of a measurement is meaningless unless it is accompanied by a description of the associated measurement uncertainty. It is therefore necessary to produce not just estimates of physical properties in a quantitative image, but also their associated uncertainties. As the process of determining a physical property from the raw MR signal is complicated and multistep, estimation of uncertainty is challenging and there are many aspects of the MRI process that require validation. With the clinical implementation of qMRI techniques and its continued expansion, there is a clear and urgent need for metrology in this field.

Clinical translation of quantitative magnetic resonance imaging biomarkers – An overview and gap analysis of current practice

“…To perform a gap analysis, we must provide a standard from which to assess the gap. That standard is established in metrology [60,106,107]. Box 2 gives an overview of metrology in relation to qMR IBs and Table 2 provides a gap analysis of relevant quality management domains and encapsulates the findings of this study with suggested best practice, the gaps and the challenges we face to bridge those gaps.…”

Repeatability and Reproducibility Uncertainty in Magnetic Resonance-Based Electric Properties Tomography of a Homogeneous Phantom

“…In order to make the result of a quantitative MRI technique a proper measurement result in the strict sense, the uncertainty with which the property values have been estimated must be assessed [ 41 ]. Up to now, only a few works have dealt with uncertainty quantification in EPT and only in theoretical cases [ 42 , 43 ].…”

Use of biexponential and stretched exponential models of intravoxel incoherent motion and dynamic contrast-enhanced magnetic resonance imaging to assess the proliferation of endometrial carcinoma

“…However, conventional MRI sequences can only assess the macroscopic morphological features of lesions, which makes it challenging to effectively evaluate features involving cellular microscopic information, such as Ki-67. Compared with conventional MRI, quantitative MRI can accurately assess the microscopic information of tissues, and with the continued progress in related technologies, an increasing number of studies have emphasized the growing contribution of quantitative MRI as a source of quantitative biomarkers (7,8). Intravoxel incoherent motion (IVIM) is a promising quantitative MRI sequence in which the biexponential model can reflect the true diffusion information and microcirculatory perfusion of water molecules in tissues, whereas the stretched exponential model describes the average diffusion information of water molecules and structural complexity in tissues (9,10).…”