PubMed · 11893647
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S Halligan. 2002. Reproducibility, repeatability, correlation and measurement error.. https://doi.org/10.1259/bjr.75.890.750193
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Functional magnetic resonance imaging (fMRI) based on both perfusion and blood oxygenation level-dependent (BOLD) contrasts has been widely applied in spatiotemporal mapping of the human brain function. Temporal resolving power of fMRI is limited by the smoothed hemodynamic response function dispersed from the neuronal activity. In this study, temporal modulation transfer functions were utilized to quantify the resolving powers of perfusion and BOLD fMR signals in time domain. The impulse response function was determined using brief visual stimulations and event-related image acquisition schemes. An important feature of arterial spin labeling techniques is that quantitative perfusion and BOLD signals could be simultaneously acquired. This simultaneous BOLD response may arise from signals that are more proximal to capillary beds, and its temporal resolution may be different from that of the typical BOLD response. Therefore, we assessed and compared the temporal resolving capabilities of perfusion, simultaneous BOLD, and the typical BOLD response obtained from the gradient echo EPI pulse sequence. Full-width-at-half-maximums of perfusion and simultaneous BOLD measurements were significantly smaller than that of BOLD ones (4.3+/- 0.6 s vs 5.5 +/- 0.9 s, p<0.02 and 4.7 +/- 1.3 s vs 5.5 +/- 0.9 s, p<0.01, respectively). The corresponding temporal resolving powers of perfusion and simultaneous BOLD signals were statistically better than that of BOLD signals (0.23 +/- 0.03 Hz vs 0.17 +/- 0.02 Hz, p<0.01 and 0.21 +/- 0.04 Hz vs 0.17 +/- 0.02 Hz, p<0.01, respectively). Our results showed that the typical BOLD response was significantly smoothed from the perfusion response, thus resulting in a degraded temporal resolving power. However, results from the simultaneous BOLD and perfusion measurements were not significantly different. Biophysical implications of the experimental outcomes were further investigated using a computer simulation based on the Balloon model. By fitting the measured data into the model, an apparently longer transit time was obtained for the typical BOLD signal (1.7 s), comparing to that for the simultaneous BOLD one (1.2 s). Therefore, the simultaneous BOLD signal was regarded as less susceptible to the variations from local draining veins. Combining the simulation result with the significantly discrepant resolving powers between the two BOLD signals, we speculated that the blurred effects from large vessels played a predominant role that further reduced the temporal resolution of the BOLD-based fMRI from the perfusion response.
Stereolithographic (SL) biomodeling is a new technology that allows three-dimensional (3D) imaging data to be used in the manufacture of accurate solid plastic replicas of anatomical structures. The authors describe their experience with a patient series in which this relatively new visualization method was used in surgery for cerebral aneurysms. Using the rapid prototyping technology of stereolithography, 13 solid anatomical biomodels of cerebral aneurysms with parent and surrounding vessels were manufactured based on 3D computerized tomography scans (three cases) or 3D rotational angiography (10 cases). The biomodels were used for diagnosis, operative planning, surgical simulation, instruction for less experienced neurosurgeons, and patient education. The correspondence between the biomodel and the intraoperative findings was verified in every case by comparison with the intraoperative video. The utility of the biomodels was judged by three experienced and two less experienced neurosurgeons specializing in microsurgery. A prospective comparison of SL biomodels with intraoperative findings proved that the biomodels replicated the anatomical structures precisely. Even the first models, which were rather rough, corresponded to the intraoperative findings. Advances in imaging resolution and postprocessing methods helped overcome the initial limitations of the image threshold. The major advantage of this technology is that the surgeon can closely study complex cerebrovascular anatomy from any perspective by using a haptic, "real reality" biomodel, which can be held, allowing simulation of intraoperative situations and anticipation of surgical challenges. One drawback of SL biomodeling is the time it takes for the model to be manufactured and delivered. Another is that the synthetic resin of the biomodel is too rigid to use in dissecting exercises. Further development and refinement of the method is necessary before the model can demonstrate a mural thrombus or calcification or the relationship of the aneurysm to nonvascular structures. This series of 3D SL biomodels demonstrates the feasibility and clinical utility of this new visualization medium for cerebrovascular surgery. This medium, which elicits the intuitive imagination of the surgeon, can be effectively added to conventional imaging techniques. Overcoming the present limitations posed by material properties, visualization of intramural particularities, and representation of the relationship of the lesion to parenchymal and skeletal structures are the focus in an ongoing trial.
The anatomical brain regions involved in the therapeutic and adverse actions of electroconvulsive therapy (ECT) are unknown. Previous studies suggest that bifrontal vs. bitemporal ECT differ in therapeutic efficacy and cognitive side effects. We therefore performed cerebral blood flow (CBF) imaging during bitemporal vs. bifrontal ECT-induced seizures to identify regions crucial for the differences between these treatments. Patients with major depression, undergoing bitemporal or bifrontal ECT, were studied. Ictal-interictal SPECT images were analyzed with statistical parametric mapping for bitemporal (n=11 image pairs in 8 patients) and bifrontal (n=4 image pairs in 2 patients) ECT-induced seizures to identify regions of ictal CBF changes. Bifrontal ECT was found to cause increases in CBF in prefrontal and anterior cingulate regions. Bitemporal ECT, however, caused CBF increases in the lateral frontal cortex and in the anterior temporal lobes. In bifrontal ECT, a greater increase in prefrontal activation, while sparing the temporal lobes, may result in a better therapeutic response and fewer adverse effects on memory than bitemporal ECT.