Assessment of the accuracy and reproducibility of adrenal volume measurements using MRI and its relationship with corticosteroid phenotype: a normal volunteer pilot study

Abstract

The significant role of corticosteroids in hypertension and cardiovascular disease highlights the importance of the adrenal gland in these disorders. The ability to correlate corticosteroid production with adrenal volume offers a novel research tool and intermediate phenotype in cardiovascular disease. The aim of this study was to develop and validate the use of magnetic resonance imaging (MRI) in adrenal volume assessment and investigate whether this associates with corticosteroid production. Twenty normotensive men underwent noncontrast 1·5T MRI scanning of adrenals, measurement of blood pressure and plasma corticosteroids. Left adrenal volume was calculated twice using standard segmentation software by four independent observers with differing levels of clinical expertise and segmentation experience. To optimize this process, adrenal 'phantoms' with known fixed volumes underwent MRI scanning and analysis by two observers. Intra-observer coefficients of repeatability (CoRs) in phantoms ranged from 0·23 to 0·43ml (interobserver CoR 0·48ml). In the subject group, mean adrenal volumes were 3·99-5·82ml with intra-observer CoRs 0·27-1·94ml. Interobserver variability was 2·73ml. Segmentation expertise was the main factor affecting variability, with experienced observers having the lowest CoRs; clinical knowledge was a factor when combined with segmentation experience. Mean adrenal volume correlated with plasma glucocorticoids (r=0·523, P<0·05) and aldosterone (r=0·515, P<0·05) for the most experienced observer only. Measurement of adrenal volume using MRI is challenging; most accurate volumes are achieved using a single observer with both segmentation experience and anatomical knowledge. The data also provide novel preliminary evidence that adrenal gland volume may be associated with plasma corticosteroid concentrations supporting further study of adrenal volume and steroid production across a range of blood pressures.