Material and Methods, SPECT Brain Perfusion Findings in Mild / Moderate Traumatic Brain Injury

SPECT BRAIN PERFUSION FINDINGS IN MILD OR MODERATE TRAUMATIC BRAIN INJURY

MATERIAL AND METHODS:

We retrospectively reviewed the record of all the patients who had a SPECT brain perfusion study between Jan 1994-Feb 1997. We identified 228 studies of patients who were status post mild or moderate TBI with or without LOC. Patients may or may not have received a CT or MRI. Any patient with a CT, or MRI, and significant important cortical atrophy or focal lesions were excluded from the study. Any patient with significant past medical history such as a previous cranial trauma, epilepsy, other previously known neurological disorders before the trauma, psychiatric diseases, HIV, drug or alcohol abuse were also excluded. In addition to the 228 studies , another 132 other SPECT brain perfusion studies were included to blind the reader and prevent bias towards the "selected group" during the review process. These additional studies included 42 studies with mild TBI and significant past medical history, 30 normal SPECTs for patients that were referred for other reasons, 30 abnormal SPECTs with documented neuro-vascular diseases, and 30 studies with severe TBI. All studies were randomized and were read twice by an expert nuclear medicine physician in the field of traumatic brain injury (HMA). No history was provided while reading the studies.

We divided the patients into 2 groups: early (i.e. imaged before 3 months after the injury), and delayed (i.e. imaged after more than 3 months but less than 3 years from the date of injury).

SPECT Procedure:

SPECT studies were performed following the IV injection of Tc-99m HMPAO (2-hour delay)¹, or Tc-99m ECD² (one-hour delay). The patients were supine with eyes open in a dimly lit, quiet room. Scanning was performed on Triple head gamma camera³, using low energy, ultrahigh resolution parallel hole collimator. The data were collected as 64 X 64 matrix, 3.56 mm/pxl, a total of 120 projections at 40 seconds / view , with a radius of rotation not to exceed 14 cm, and as close to head as possible. The raw data was smoothed with Butterworth filtered Nyquist (cyc/cm) of 1.404, and high cutoff frequency of 0.56 cyc/cm. The reconstruction was performed with ramp filter Nyquist (cyc/cm) of 1.404, and high cut frequency (cyc/cm) of 1.404. The uniform attenuation was applied. The images were then reoriented in the axial, coronal and sagittal planes. The final data was displayed 2 pixels thick (7.4 mm) on 10 graded color scale. The cerebellum was used as the reference site for 100% maximum value of the maximum cerebellar uptake, and studies with cerebellar abnormalities were excluded. The brain was divided into 24 distinct regions: R and L caudate nuclei; R and L thalami; R and L putamen; R and L anterior frontal lobes; R and L superior frontal; R and L inferior frontal; R and L anterior temporal; R and L medial temporal; R and L lateral temporal; and R and L cerebellum. The R and L insular region and R and L occipital regions. Any measurement of cerebral perfusion in the cortex or basal ganglia under 70%, or 50% in the medial temporal was considered abnormally decreased ⁽³²⁾.

Statistical Analysis:

Statistical Analysis was done by a two-tailed T-test from available commercial software - EXCEL from Microsoft which returns the probability associated with a Student's T-test. The T-test studied a hypothesis which states that the two samples were likely to have come from the populations that have the same mean.