Source image

Coutts SB, Lev MH, Eliasziw M, Roccatagliata L, Hill MD, Schwamm LH, Pexman JH, Koroshetz WJ, Hudon ME, Buchan AM, Gonzalez RG, Demchuk AM. ASPECTS on CTA source images versus unenhanced CT added value in predicting final infarct extent and clinical outcome. Stroke 2004 35 2472-2476. 

Review of postcontrast CTA source images might provide a good estimate of whole-brain perfusion." If time allows, MR or CT perfusion maps are obtained to characterize more accurately the ischemic penumbra." Careful but expedited preprocedural analysis of the CTA, done in parallel with transport of the patient to the treatment area, may be extremely helpful in establishing the presence of anatomic variants (e.g., bovine aortic arch) or pathological states (e.g., vessel origin or carotid bifurcation disease) prior to the catheterization procedure. 

Also, for parallel multichannel devices, the source image can be divided, and injected simultaneously into a number (for example up to eight) of output fibers. Alternatively for more demanding diffuse reflectance or diffuse transmission applications with much lower optical throughput, the whole source image dimension can be used, but injected into micro- or macrobundle fiber optics. 

In general the physical dimensions of the source image, as it is focused onto the fibre input, even when the NAs are matched will be larger than the fibre diameter, and there will be consequent injection losses for smaller diameter fibres. However, these may be compensated for by the fact that the spread of input angles, when the source image is... 

The reflected ray may also be constructed by considering the mirror image of the source as reflected across the plane of the wall. In figure 3.2, the image source thus constructed is denoted AThis technique of reflecting sources across wall surfaces is called the source image method. The method allows a source with reflective boundaries to be modeled as multiple sources with no boundaries. 

The simplifying assumptions that permit us to consider only specular reflections are no longer met when the wall surfaces contain features that are comparable in size to the wavelength of the sound. In this case, the reflected sound will be scattered in various directions, a phenomenon referred to as difjusion. The source image model cannot be easily extended to handle diffusion. Most auralization systems use another geometrical model, called ray tracing [Krokstad et al., 1968], to model diffuse reflections. A discussion of these techniques is beyond the scope of this paper. 

This is possible because the projection lens system, which for clarity was not shown in Figure 4.7, is normally included behind the objective lens and below the source image plane. This lens system allows the projection of both the diffraction pattern and the specimen image on the observation screen. In Figure 4.8, [50] the electron diffraction pattern of a Fe thin film is shown. In Figure 4.9, the transmission electron micrograph of the mordenite included in the sample CMT-C (see Table 4.1), where fiber-like crystals of mordenite are seen, is shown [51],... 

Figure 3 Diagram of the ion source imaging instrument. The spatially resolved ion beam is projected onto the image intensifier to produce an image of the ion emitting regions of the emitter.

Fig. 5.8a,b. Assumed signal intense plaque (a). Source image of TOF-MRA at the level of the carotid bulb displays bright material, ultrasound showed no evidence of a thrombus. On CE-MRA there is a short eccentric stenosis of the left ICA (b)... 

The anterior choroidal artery is mostly detectable only on source images, not on MIP of a TOF-MRA (Wiesmann et al. 2001), because of its very small size. Consequently, definite statements about pathology can not be made. 

Superior to DSA, MRI can depict arterial flow or lumen as well as the vessel walls. Analysis of plaque morphology was improved in recent years by the development of specific MRI techniques. Plaques can now be characterized in vivo with regard to fibroid or lipid content or hemorrhagic lesions (Fig. 5.8). It can be expected that, in the future, plaque examination will influence stroke treatment protocols if the risk of plaque rupture can be reliably estimated (Cappendijk et al. 2005 Hayes et al. 1996 Trivedi et al. 2004 Yuan et al. 2001). Plaque examinations, however, are not yet clinical routine. Source images of TOF-MRA allow only limited assessment of vascular walls. 

Fig. 5.23a-c. Carotid dissection. While the characteristic intramural hematoma is easily recognized as bright on TOF-MRA source images (a) and MIP (b), CE-MRA (c) outlines the long high grade stenosis of the distal extracranial vessel, but not the hematoma itself... 

Fig. 5.24a-c. Moya Moya syndrome. TOF-MRA demonstrates on source images (a,b) and MIP image (c) multiple small collateral vessels and distal occlusions of the carotids... 

Fig. 6.1. Source images of a dynamic susceptibility contrast-enhanced series in a healthy volunteer, acquired 20-50 s after bolus injection during the bolus passage the signal decrease in gray matter is more prominent than that in white matter. After the bolus passage, the signal returns to normal...

Do not rely on MIP images without looking at the source images. The information loss may be crucial as visualized in Fig. 18.10. 

Reite M, Sheeder J, Teale P, Adams M, Richardson D, et al. 1997. Magnetic source imaging evidence of sex differences in cerebral lateralization in schizophrenia. Arch Gen Psychiatry 54(5) 433-440. 

SOURCE Image courtesy of G. Tayhas Palmore, Brown University. 

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