Application of stereological estimates in patients with severe head injuries using CT and MR scanning images

Abstract

Severe brain damage is often followed by serious complications. Quantitative measurements, such as regional volume and surface area under various conditions, are essential for understanding functional changes in the brain and assessing prognosis. The affected brain tissue is variable, hence traditional imaging methods are not always applicable and automatic methods may not be able to match the individual observer. Stereological techniques are alternative tools in the quantitative description of biological structures, and have been increasingly applied to the human brain. In the present study, we applied stereological techniques to representative CT and MRI brain scans from five patients to describe how stereological methods, when applied to scans of trauma patients, can provide a useful supplement to the estimation of structural brain changes in head injuries. The reliability of the estimates was tested by obtaining repeated intra- and interobserver estimates of selected subdivisions of the brain in patients with acute head injury, as well as in an MR phantom. The estimates of different subdivisions showed a coefficient of variation (CV) below 12% in the patients and below 7% for phantom estimation. The validity of phantom estimates was tested by the average deviation from the true geometric values, and was below 10%. The stereological methods were compared with more traditional region-based methods performed on medical imaging, which showed a CV below 7% and bias below 14%. It is concluded that the stereological estimates may be useful tools in head injury quantification.

Figure 1

MR phantom estimation. Five objects of different diameter are shown in (a). Purple = 20 cm diameter; green = 6 cm diameter; red = 3 cm diameter; yellow = 1.5 cm diameter, and turquoise = 1 cm diameter. (b) Point counting grids with difference area per point for volume estimation. This is an example for the phantom 1 cm in diameter. (c) As the phantoms are spherical and isotropic, perpendicular test lines were used to estimate surface. Only red lines intersect with the surface. This is an example for a phantom 6 cm in diameter.

Figure 2

Scanning image examples. Acute (CT) and follow-up (FU) (MR) scanning images from Patient 2.

Figure 3

Stereological grids. (a) Points used for volume estimation (Cavalieri's method). All brains were divided into unaffected tissue (red), lesion (turquoise) and haematoma (yellow) and were counted simultaneously. (b) Test lines used for surface estimation. All intersections between the borders of neocortical matter and the test line were counted. Red = one intersection; turquoise = two intersections; and green = three intersections. It was assumed that there was isotropy.

Figure 4

Simulated stereology on BrainWeb data. Automated point counting was performed of different brain compartments using the BrainWeb anatomical brain model. All possible grid positions and 10 starting slice positions were tested using an in-plane point spacing varying between 1 mm and 30 mm, and 10 slices equally spaced over the entire brain. Points were assigned to a given compartment if the BrainWeb probability for that compartment was more than 50. The total volume for each compartment was calculated using Equation 1, and CV for each grid density was calculated according to Equation 9. gm, grey matter; wm, white matter; csf, cerebrospinal fluid; icv, total intracranial volume.