A Method for Rapid Volumetric Analysis of Structural Magnetic Resonance Images of the Brain

Article excerpt

ABSTRACT

Objectives: To describe the methodology for volumetric analyses of brain volumes in vivo by structural magnetic resonance imaging. To assess the reliability and validity of the volumetric technique.

Methods: Patients were recruited for magnetic resonance imaging as part of a wider project studying biological determinants of psychosis. Volumetric analysis of brain scans was performed blind using a rapid automated in-house software package to remove non-brain elements (scalp-editing), and to calculate volumes of the whole brain, lateral ventricles, cerebrospinal fluid, and cortical gray and white matter compartments.

Results: Quantitative analyses of each magnetic resonance imaging scan took approximately 45 minutes for each patient (between-group results will be reported later). Test-retest reliability for 20% of scans selected at random was generally high. Spearman's rank correlation coefficient (rho) for whole brain was 0.99, grey matter was 0.79, white matter was 0.86, cerebrospinal fluid and sulcal compartment was 0.83 and lateral ventricle was 0.86. Inter-rater reliability by two independent assessors for the same sample of scans was high at 0.99 for whole brain and moderate for the other measures (grey matter and white matter was 0.62, cerebrospinal fluid and sulcal compartment was 0.60, lateral ventricle was 0.67). Face validity of the three-dimensional brain was good. An independent phantom analysis (measuring the volume of an object of known volume and intensity compartments) suggested that the estimated volumetric techniques were accurate to 97% and 98%, respectively.

Conclusion: This method is reliable, valid, and fast for the purpose of quantification of cerebral morphology on magnetic resonance imaging scans. We propose that it can be employed for the assessment and monitoring of neuropsychiatric disorders in which cerebral volumetric change occurs.

Keywords: Brain; Cerebral; Magnetic Resonance Imaging; Volume; Volumetric.

INTRODUCTION

Quantitative analysis of magnetic resonance imaging (MRI) brain images in vivo has became increasingly objective, fast and user-friendly. Traditional methods of volumetric analysis have depended upon manual tracing of regions of interest, but this is impractical for large data sets such as thin-slice contiguous images of the entire brain. These techniques are labour intensive, subject to individual bias, and based upon a priori hypothesis of regions of interest. In comparison, automated techniques are able to measure the whole data set in a fraction of the time previously required, utilise objective measurement algorithms, and, more importantly for complex disorders such as schizophrenia, there is no need to select regions of interest so that potentially useful data need not be discarded.

In recent years, there has been a wealth of studies which support the existence of cerebral morphological abnormalities in schizophrenia. (1,2) Of these the best-replicated finding is lateral ventricular enlargement; other changes which are somewhat more contentious include sulcal widening and cortical grey matter reduction. (3) One explanation contributing to the inconsistency in the literature is that different groups have employed different volumetric techniques. In this paper, we describe in detail the methodology for brain volumetric analysis, and endeavour to assess whether it is a reliable and valid method. The volumetric analysis method (General Electric Advantage Windows Version 2.0) described is utilised for clinical diagnostic purposes, thus it is necessary to ascertain its reliability and validity as a research tool.

AIM

We aimed to demonstrate the use of in-house software to conduct volumetric analyses of the following brain volume parameters: whole brain volume, cerebrospinal fluid (CSF), lateral ventricles, and cortical grey and white matter.

METHODS

PATIENTS

The study enrolled patients admitted to the Queen Mary Hospital or Pamela Youde Nethersole Eastern Hospital, who were participating in a wider project to study the biological determinants of psychosis in a consecutive sample of patients with a first episode of psychosis (the results of which will be reported separately). …