Patient motion

Using the currently available rod sources, the above method requires the transmission scan to be taken before the emission scan and obviously requires a long time to acquire enough counts for good accuracy of the measured attenuation correction factors. An alternative to this approach is to collect the transmission scan postinjection immediately after the emission scan without moving the patient from the bed. This method obviates the need for patient repositioning and hence the need for correction for patient motion... 

Several factors affect the contrast of an image, namely count density, scattered radiations, type of film, size of the lesion, and patient motion. Each contributes to the contrast to a varying degree. These factors are briefly discussed here. 

Since this technique relies on detecting the highest pixel on a given ray, it is sensitive to overlap from adjacent bony and opacified venous structures, as shown in Fig. 4.12. Currently, attempts are being made to subtract the underlying bony structures, but to date these have been limited by multiple technical factors, not least of which is subtle patient motion resulting in inaccurate representation of the composite image. 

Potential pitfalls in the computation of CBF using deconvolution methods include patient motion and partial volume averaging, which can cause underestimation of the AIF(f). Image coregistration software to correct for patient motion and careful choice of ROIs for the AIF can minimize these pitfalls. 

D time of flight (3D TOF) Noninvasive High spatial resolution Shows complex vascular flow Less susceptible to intravoxel dephasing Can be repeated if suboptimal Can be obtained after contrast Only small volumes due to marked saturation effects Cannot image slow flow because of saturation effects Time-consuming, susceptible to patient motion Artifact from T1 hyperintense lesions Routine to evaluate circle of Wfllis for large vessel stenoses/ occlusions Can estimate carotid bifurcation stenoses... 

MRA performs reasonably well in detecting major vessel occlusion, but is prone to patient motion and flow-related artifact. Additionally, it is less sensitive for detecting M2 occlusions... 

Scanning with a minimum of artifacts due to patient motion and other causes. 

Interventional procedures can be affected by patient motion or organ movement due to respiration (Xu et al. 2005). Thus, target movement must be recognized and accurately tracked, in addition to the constant calculation of the actual trajectory of a needle guide, based on the internal sensor systems of the robot. 

Commercially available PET-CT scanners are based on the imaging principle described by Beyer et al. (2000). Two separate scarmers, a CT and a PET, are installed in series. A single examination table serves both imaging components of the PET-CT (Fig. 33.4). The patient is positioned on the examination table this is followed by acquisition of the CT, and then by acquisition of the PET. In between the two scans, the patient remains in the same position on the examination table. This assures that morphological and functional data sets can be accurately fused after image acquisition. Patient motion in between the two scans or motion of internal organs may result in different positions of an organ or a lesion... 

Apart from organ movement and patient motion, inaccuracies in image co-registration may result from differences in image acquisition with CT and PET. CT data are acquired with continuous table movement over a very short period, typically allowing coverage of a... 

HIFU and achieved partial or total success in 73% of cases. They described problems due to patient motion, lesion undertreatment through inadequate power settings, and beam reflection caused by the formation of gas bubbles during treatment or local anesthetic. 

Sometimes a 2nd ( passive) arm is strqiped to patient to monitw patient motion, on othma a number of markers are tracked by an extmnal camera system. Target location on a quantitative model is iqrdated in real time to idlow surgeon to track target with tool on turn. 

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