Biomedical subjects

Rudi Dierckx

Publications and source records attributed to Rudi Dierckx.

40 records · Page 3Linked to original sources

PubMed2002

Analysis of clinical brain SPECT data based on anatomic standardization and reference to normal data: an ROC-based comparison of visual, semiquantitative, and voxel-based methods.

UNLABELLED: The technique of anatomic standardization and comparison with normal templates is increasingly used in clinical brain SPECT practice and allows automated, operator-independent volume-of-interest (VOI) or voxel-based analysis of whole-brain data. In 2 distinct clinical populations with severe traumatic brain injury and cognitive impairment, this study compared 3 widely available approaches that use normal templates to evaluate SPECT brain perfusion deficits. METHODS: In total, 74 subjects were studied. These included 14 patients with severe, traumatic brain injury (group 1; 10 males, 4 females; mean age +/- SD, 27.6 +/- 8.2 y) and 15 patients with cognitive impairment (group 2; 7 males, 8 females; mean age, 75.8 +/- 8.6 y). These data were compared with those from, respectively, 25 and 20 age- and sex-adjusted healthy volunteers. All data were analyzed in 4 ways. Three semiquantitative statistical algorithms were used: statistical parametric mapping (SPM) using SPM99, brain registration and analysis of SPECT studies (BRASS) using a voxelwise region-growing technique, and a predefined VOI approach. These results were compared with visual analysis based on consensus reading by 3 experienced nuclear medicine physicians. Receiver operating characteristic (ROC) analysis was performed at various statistical cutoffs. Moreover, as a measure of regional agreement, relative regional agreement between methods was assessed. RESULTS: In both study groups, BRASS voxel-based analysis was most accurate, as defined by the area under the ROC curve (0.97 for group 1 and 0.96 for group 2). VOI assessment was slightly more accurate than visual consensus analysis, whereas SPM showed, overall, a lower area under the ROC curve. SPM analysis was also significantly less sensitive at thresholds corresponding to low false-positive fractions. Regional analysis showed 83%-92% agreement between all methods. CONCLUSION: Under clinical conditions, classification of brain SPECT studies can greatly be aided by anatomic standardization techniques and reference to normal data. Under the investigated circumstances, SPM was found to have a lower sensitivity than VOI or voxelwise region-growing techniques, especially at low false-positive fractions.

Adolescent↗

PubMed2002

Perfusion SPECT changes after acute and chronic vagus nerve stimulation in relation to prestimulus condition and long-term clinical efficacy.

UNLABELLED: Left-sided vagus nerve stimulation (VNS) is an efficacious treatment for patients with refractory epilepsy. Previous studies have implicated thalamic and mesial temporal involvement in acute stimulation. In this study, acute and chronic effects of VNS in patients with refractory complex partial seizures with or without secondary generalization (CPS +/- SG) were evaluated with respect to the prestimulus condition and long-term follow-up. METHODS: Twenty-three patients (12 females, 11 males; mean age, 32.4 +/- 10.6 y; mean CPS +/- SG duration, 21.0 +/- 11.7 y) were prospectively included. All patients were considered unsuitable candidates for resective surgery because of nonlocalizing findings in the presurgical evaluation. All underwent a split-dose (99m)Tc-ethyl cysteinate dimer activation study before and immediately after their initial stimulation (0.25 or 0.5 mA, 30 Hz) on a high-resolution triple-head gamma camera. Ten patients also underwent a SPECT activation study 5.7 +/- 1.6 mo after implantation with an additional 0.25-mA stimulus superposed on a therapeutic intensity of 1.5 +/- 0.3 mA. Data were analyzed by an automated semiquantitative volume-of-interest analysis after stereotactic anatomic standardization. RESULTS: In the acute, initial setting, the left thalamus, right parahippocampal gyrus, and right hippocampus were deactivated by VNS (P < 0.011). Acute stimulation in the chronic state resulted in a significant left thalamic activation (P < 0.001). When chronic perfusion was compared with the initial pre-VNS baseline, perfusion decreases were found in both thalami (-5.3% on the left and -3.4% on the right, P < or = 0.04). Perfusion changes in chronic VNS correlated negatively with the prestimulus perfusion pattern, indicating the tendency toward decreased brain activity on VNS. Initial stimulation changes in the right amygdala in the group of 10 patients with chronic assessment were predictive of therapeutic response (P = 0.018); in addition, right chronic hippocampal perfusion changes correlated strongly with the long-term clinical efficacy of VNS (P = 0.004). CONCLUSION: Under initial and chronic conditions, acute VNS stimulation produces different perfusion changes that are related to the interictal perfusion pattern before stimulation. The long-term mechanism of clinically effective VNS may rely on mainly hippocampal/amygdala and thalamic inhibition. Acute amygdala and chronic hippocampal perfusion changes are predictive of long-term therapeutic response in specific patient subgroups.

Adult↗

PubMed2002

18 F-Fluorodeoxyglucose triple-headed coincidence detection imaging in oncology: preliminary results and comparison with dedicated PET.

BACKGROUND: Dual head coincidence (DHC) imaging has been proposed as a valuable and cheaper alternative to oncological PET. The increased sensitivity of the recently-developed triple-headed gamma camera (THC) optimized for coincidence detection has not been either validated or compared to the sensitivity of a dedicated PET system in a clinical study. MATERIAL/METHODS: Differences in contrast-to-noise-ratio (CNR) between dedicated FDG PET, DHC and THC imaging were assessed using a hot sphere phantom. Twenty-two oncological patients were prospectively studied with consecutive whole body FDG PET and FDG THC imaging. The images were visually read by 2 experienced nuclear medicine specialists. The diagnostic sensitivity of FDG THC imaging was assessed using FDG PET as the imaging gold standard. Lesion size was determined using computed tomography or magnetic resonance imaging. RESULTS: The mean gain in CNR for THC as compared to DHC imaging was 35% (10-56%). Of 63 lesions, 58 (92%) on FDG PET were also detected with THC imaging. Considering only lesions smaller than 15 mm, the relative sensitivity was 86% (24/29). All lesions above 15 mm (n=34) were detected using THC imaging. CONCLUSIONS: The first clinical results for THC imaging are promising. The overall relative sensitivity in this limited series was 92%. Only a few lesions smaller than 15 mm were missed.

Adult↗

PubMed2002

Toward clinical application of neuropsychological activation probes with SPECT: a spatial working memory task.

UNLABELLED: The concept of working memory is central to theories of human cognition, because it is essential to human skills such as decision making and deductive reasoning. Although PET and functional MRI have provided robust data on the recruitment of specific pathways in working memory tasks, the experimental settings of these studies may not be transferable to a clinical situation. Hence, to develop neuropsychological SPECT activation probes that are suitable for daily clinical practice, this study reports on a neuropsychological activation task of spatial working memory under classical neuropsychological test conditions in healthy subjects. METHODS: Reaction times and accuracy were measured as behavioral parameters and functional imaging data were analyzed with statistical parametric mapping to determine significant voxel-wise changes between the perception task and the memory task. RESULTS: Subjects reacted more slowly and performed less accurately during the memory task compared with the perception task, findings that are in keeping with other neuropsychological studies. Also, the overall pattern of brain activations revealed in our experiment is consistent with the data of the literature, thereby validating our test probe. CONCLUSION: From a practical viewpoint, the close resemblance of the test conditions of the SPECT procedure with those of the investigation room and the relative simplicity of the task under study probably constitute major advantages for future clinical application of the SPECT procedure in patients with cognitive impairments.

Adult↗