Mario Quarantelli Biostructure and Bioimaging Institute – CNR Naples - Italy

1. Cortical GABA-A CBZR and rCBF in Alzheimer`s disease: SPET studieswith Partial Volume Effect Correction Mario Quarantelli Biostructure and Bioimaging Institute – CNR Naples - Italy HBM2004 - PVEOut Satellite Meeting Budapest, 12 June 2004 IBB, 2004

2. CBF The progression from Mild Cognitive Impairment (MCI) to Alzheimer’s Disease (AD) is characterized by the increase in severity and extension of cerebral hypometabolism and regional cerebral blood flow (rCBF) [Nestor 2003], already detectable in posterior cingulate, hippocampus and temporal neocortex in MCI patients.Concurrently, gray matter (GM) loss, essentially limited to hippocampal cortex in MCI [Chetelat 2002], progresses into a more widespread cortical loss. • Chetelat G, et al. Neuroreport 2002; 13:1939-1943 • Nestor PJ, et al. Ann Neurol 2003;54:343–351 IBB, 2004

3. CBF It is not currently known weather this pattern of progression is characterized by a strict coupling of these two phenomena (i.e. GM loss explains the metabolism reduction as detected by FDG-PET and rCBF-SPET studies), or if metabolic impairment exceeds the rate of GM loss.Aim of our study was to compare rCBF decrease independently of GM loss in two groups of MCI and AD patients, using a ROI-based method for partial volume effect (PVE) correction which takes into account both WM and CSF. IBB, 2004

4. CBF - METHODS • 12 MCI subjects (mean age 74.8 yrs, MMSE 27.8 range 24.9-30) • 10 AD patients (mean age 79.5 yrs, MMSE 21.2, range 16.9-24) • SPECT: • 64-slice brain-dedicated SPECT • 20-30 min after 740-1110 MBq of 99mTc-HMPAO • 120 steps, 3° angular step, 15 sec per step, 128 x 128 matrix, pixel size 1.673mm, Butterworth filter (cut-off = 0.9 cm-1, order=10), attenuation correction (0.120 cm-1) using Chang’s algorithm [Chang, 1987]. • Final FWHM 10.4mm (6mm axial) • MRI: • Magnetization-prepared 3D T1-weighted fast-GrE images, TR/TE/TI 11/2/600ms, 1.5T, voxel size 0.98x0.98x1.2mm • Probabilistic MRI segmentation [Ashburner J, 2000] and co-registration to SPECT studies [Friston KJ, 1995]. • Ashburner J, Friston KJ, NeuroImage 2000; 11:805-21 • Chang, L. IEEE Trans Nucl Sci 1987;25: 638-643 • Friston KJ, et al. Hum Brain Map 1995; 2:165–189 IBB, 2004

5. CBF - METHODS • VOI including cerebral lobes and hippocampus for each side, and a single region for cerebellum and posterior cingulate, were defined in the MNI space and adapted to each co-registered segmented GM using normalization parameters derived from the SPM99 affine normalization matrix [Berkouk 2003]. • For each VOI, uncorrected and PVE-corrected mean tracer concentrations were calculated [Rousset OJ, 1998; Quarantelli M, 2003] and normalized by corresponding cerebellum values. • Comparison between MCI and AD groups was carried out for each region by Student's T-test. Significance level was set to P<0.05. • Berkouk K, et al. 2003 HBM meeting; Abs. 1017 • Quarantelli M, et al. J Nucl Med. 2004;45:192-201 • Rousset OG, et al. J Nucl Med 1998;39:904-911 IBB, 2004

6. 77yo MCI IBB, 2004

7. 77yo AD IBB, 2004

8. CBF - Methods IBB, 2004

9. CBL-normalized rCBF(AD-MCI) / MCI Mean percentage reduction in AD compared to MCI patients. Data are reported before (uncorrected) abd after (corrected) correctionfor partial volume effects. Significant differences (P<0.05) are in yellow. IBB, 2004

10. CBF – CONCLUSIONS • Metabolic/CBF changes in AD are paralleled by GM loss [Baron JC, 2001a; Karas GB, 2003]. Accurate voxel-based comparisons of these changes have shown that the atrophy explains the GM hypometabolism with the exception of the posterior cingulate [Baron JC, 2001b], an area known to be affected precociously in AD [Minoshima S, 2000]. • Our results integrate these findings, showing in PVE-corrected rCBF-SPET data from AD patients, as compared to MCI, a similar pattern of posterior cingulate involvement independent of GM loss.Reduced metabolism in these regions may be related to remote functional disruption and/or by larger neuronal loss than expected from structural changes. • While larger cohorts are needed to confirm these preliminary findings, longitudinal studies are needed to confirm this pattern of progression of the disease. • Baron et al, NeuroImage 2001b; 13:S771 • Baron JC, et al. Neuroimage 2001a ; 14:298-309 • Karas GB, et al. Neuroimage 2003; 18:895-907 • Minoshima S, et al. Ann Neurol 1997, 42 :85-94 IBB, 2004

11. Cortical GABA-A CBZR loss measured with 123I-Iomazenil in Alzheimer’s disease: a SPECT study with Partial Volume Effect correction Cortical synaptic/neuronal loss has been reported in neuropathological studies of patients with AD and may contribute to GM density changes described recently in AD using VBM analysis of structural MRI. PET/SPECT markers of GABA-A central benzodiazepine receptors (cBZR) have been proposed to detect in vivo early cortical synaptic/neuronal loss in AD. Only few studies have been reported with discordant results [Meyer M et al, Arch neurol 1995; 52:314 - Soricelli A, et al. Eur J Nucl Med 1996;23:1323] IBB, 2004

12. GABA-A CBZR Aim of the study was to investigate whether cortical synaptic/neuronal loss may be detected in vivo in AD using SPECT with 123I-Iomazenil and to assess how the measurement of these receptor changes is affected by partial volume effect (PVE). For this we used a voxel-based method for PVE-correction which takes into account both WM and CSF. • Müller-Gartner HW, et al. J CBF Metab 1992;12:571-583 • Quarantelli M, et al. J Nucl Med. 2004;45:192-201 IBB, 2004

13. GABA-A CBZR IBB, 2004

14. GABA-A CBZR • 5 AD patients (NINDS-ADRDA criteria; mean age 70 ± 11 yrs, MMSE: 19±4) • 8 patients with MCI (74±6.5 yrs, MMSE: 27±2) • 3 healthy volunteers (60±5 yrs, MMSE: 30) • 20 minute SPECT acquisition, 180 min after injection • brain-dedicated camera (Ceraspect; 64 transaxial slices; voxel size 1.673 mm • Attenuation correction (Chang’s algorithm, attenuation factor 0.120 cm-1) • These 'late images' were assumed to reflect essentially receptor binding. • MRI: 1.5T, CSE sequences providing 32 T1w (600/15) and PD/T2w (2400/15-90) 4mm-thick axial images; Multiparametric segmentation • GM, WM and CSF maps were co-registered to SPECT studies. • VOI including frontal, parietal, temporal, and occipital lobes, hippocampus and posterior cingulate cortex for each side, and a single region for cerebellum, was defined in the MNI space and adapted to each co-registered segmented GM using the SPM99 affine normalization matrix. • Uncorrected and PVE-corrected mean tracer concentrations were normalized by corresponding cerebellum values. • Two tailed Student's T-test on CBL-normalized values. • Significance level was set to P<0.05. IBB, 2004

15. CBZR preliminary results Before PVE-correction AD vs NV reduction bilaterally in all cortical regions except the occipital and right frontal cortices and left hippocampus MCI vs NV reduction in the left posterior cingulate and a trend in the right posterior cingulate. AD vs MCI reduction of 123I-Iomazenil bilaterally in the parietal and temporal cortices and posterior cingulate and in the right hippocampus. IBB, 2004

16. CBZR preliminary results After PVE-correction AD vs NV reduction in the posterior cingulate bilaterally and in the left hippocampus MCI vs NV No significant differences AD vs MCI reduction in the posterior cingulate bilaterally IBB, 2004

17. ## ## ## ## # # # # # # # # # # # # # # # # ** ** ** ** # # # # ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** ** * * * * * * * * # # # # * * * * 123-Iomazenil before PVE correction in AD, MCI and Controls (C). Significant reduction in AD vs Controls= * p<0.05: ** p<0.01 Significant reduction in AD vs MCI s= # p<0.05; ## p<0.01. IBB, 2004

18. 123-Iomazenil after PVE correction in AD, MCI and Controls Significant reduction in AD vs Controls= * p<0.05: ** p<0.01 Significant reduction in AD vs MCI = # p<0.05; ## p<0.01 IBB, 2004

19. CBZR - Conclusions • These preliminary results provide two interesting observations: 1) In AD patients the GABA-A-cBZD receptors are significantly reduced as compared to Controls and MCI in associative cortical areas including the hippocampus. 2) This reduction survives the PVE-correction in some cortical areas particularly vulnerable in AD (posterior cingulate cortex and, to a lesser extent, the hippocampus). • Overall these findings suggest that GABA-A-cBZR alterations in AD parallel but also exceed structural changes as measured by MRI segmentation. Further data are required to confirm these findings in larger groups of subjects IBB, 2004