Controlling for premorbid brain size in imaging studies: T1-derived cranium scaling factor vs. T2-derived intracranial vault volume

• Published in: Psychiatry research Vol. 131; no. 2; pp. 169 - 176
• Main Authors: Fein, George, Di Sclafani, Victoria, Taylor, Colin, Moon, Kirk, Barakos, Jerome, Tran, Hoang, Landman, Bennett, Shumway, Robert
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 30.07.2004; Elsevier
• Subjects: Adult; Age Factors; Aged; Alcoholism - pathology; Atrophy; Biological and medical sciences; Black or African American; Black People; Brain - pathology; Brain atrophy; Cocaine-Related Disorders - pathology; Cross-Sectional Studies; Female; Humans; Image Processing, Computer-Assisted; Intracranial vault; Investigative techniques, diagnostic techniques (general aspects); Magnetic Resonance Imaging; Male; Mathematical Computing; Medical sciences; Middle Aged; Nervous system; Premorbid brain size; Radiodiagnosis. Nmr imagery. Nmr spectrometry; Reference Values; Reproducibility of Results; Sensitivity and Specificity; Sex Factors; SIENAX; Skull - pathology; White People; SIENAX; Intracranial vault; Premorbid brain size; Brain atrophy; Human; Intracranial; Central nervous system; Nuclear magnetic resonance imaging; Ethnic group; Encephalon; Investigation method; Morphology; Developmental stage; Sexual dimorphism; Vault; Morphometry; Age; Comparative study
• ISSN: 0925-4927; 0165-1781; 1872-7506
• DOI: 10.1016/j.pscychresns.2003.10.003

Intracranial vault (ICV) volume, obtained from T2-weighted magnetic resonance imaging (MRI), is generally used to estimate premorbid brain size in imaging studies. T1-weighted sequences lack the signal characteristics for ICV measurements [they have poor contrast at the outer boundary of sulcal cranium scaling factor (CSF)] but are valuable in imaging studies due to their excellent gray vs. white matter contrast. Smith et al. [NeuroImage 17 (2002) 479] suggested a T1-derived cranium scaling factor as an alternative control variable for premorbid brain size in cross-sectional studies. This index, which is computed using the SIENAX software, is a scaling factor comparing an individual's skull to a template skull derived from the Montreal Neurological Institute (MNI) average of 152 T1 studies (the MNI152). SIENAX computes coarsely defined estimates for the individual and MNI skulls rather than well-defined volumes. To test how well this approach would work as a control variable for premorbid brain size in cross-sectional studies, we compared the T1-derived cranium scaling factor to T2-derived ICV measurements in a sample of 92 individuals: 39 white males, 22 white females, and 31 African-American males, with an age range of 26–78 years. The correlation between T1- and T2-derived variables was 0.94 and did not differ across subject groups. The T1-derived cranium scaling factor accounted for a statistically significant portion (87%) of the variance of the T2-derived ICV measure and thus is a good surrogate for ICV measurement of premorbid brain size as a reference measure in MRI atrophy studies. Furthermore, neither race, sex, nor age accounted for any additional variance in ICV, indicating that neither race-, gender-, nor age-associated cranial bone thickness effects were present in this data set.