Image acquisition protocols

With a properly selected image acquisition protocol, state-of-the-art C-arm CT systems such as syngo DynaCT (Siemens AG, Healthcare Sector, Forchheim, Germany) can at least resolve 5-mm (10-mm) diameter objects with a contrast difference of 10 HU (SHU) (Fahrig et al. 2006). Even better results are sometimes possible as demonstrated in Fig. 3.5. From a chnical point of view, the low-contrast imaging performance of today s C-arm systems not only can be expected to differentiate between fat and muscle tissue, but C-arm CT can also resolve smaller contrast differences and possibly even visuahze bleeds. 

The technique of mid-IR microspectroscopy and imaging has great potential for the rapid and reliable identification of tissue structures not only for scientific research purposes but also in a real clinical set-up. The standardisation of the data acquisition and the assessment of the quality of the spectra constitute key factors for the successful transfer to elinical application. Furthermore the problem of overfitting and the role of independent validation have been discussed. In this chapter we also exemplified the question of standardisation of the hyperspectral image acquisition protocol and demonstrated how the... 

Ga-DOTATOC (150-210 MBq) or 68Ga-Bombesin (3 nmol) is usually injected into adult patients for receptor imaging (see Notes 2-4). The acquisition protocols are the same as in FDG. If different tracer studies are planned, the studies should be performed at different days to avoid background activity due to the decay of the injected isotope. 

This chapter will discuss the role of CTA in the diagnosis and triage of acute stroke patients. First, the general principles of helical CT scanning will be reviewed, including image acquisition and reconstruction techniques. The stroke CTA protocol will then be described, followed by specific issues regarding the accuracy and clinical utility of stroke CTA. 

The technical considerations and interpretation of the second portion of the acute stroke protocol, CTA, is discussed in detail in Chap. 4. Importantly, however, the source images from the CTA vascular acquisition (CTA-SI) also supply clinically relevant data concerning tissue level perfusion. It has been theoretically modeled that the CTA-SI are predominantly blood volume, rather than blood flow weighted [20, 27,70], The potential utihty of the CTA-SI series in the assessment of brain perfusion is discussed in detail below. This perfused blood volume technique requires the assumption of an approximately steady state level of contrast during the period of image acquisition [27], It is for this reason - in order to approach a steady state - that protocols call for a biphasic contrast injection to achieve a better approximation of the steady state [71, 72]. More complex methods of achieving uniform contrast concentration with smaller doses have been proposed that may eventually become standard, such as exponentially decelerated injection rates [73] and biphasic boluses constructed after analysis of test bolus kinetics [72, 74]. 

Image Acquisition Parameters. The CTP imaging protocol has always been performed at 80 kV, rather than the more conventional 120-140 kV. Theoretically, given a constant mAs (typically 150-200), this kV setting would not only reduce the administered radiation dose to the patient, but would also increase the conspi-cuity of rv contrast, due, in part, to greater importance of the photoelectric effect for 80 kV photons, which are closer to the k-edge of iodine [35],... 

The ideal volumetric dataset, which respect precisely the imaged structures, is obtained when all voxels are isotropic, and therefore their shape is cubic. Unfortunately conventional CT and spiral CT did not fulfill completely these acquisition requirements. Dedicated MR sequences and multi-row detector CT (over 16 slices) overcome this limitation generating isotropic voxels and reducing motion artifacts thanks to faster acquisition protocols. 

Jager et al. (2005), equipped with a four-slice scanner, report the following acquisition protocol in the axial plane (0.5 mm section thickness 0.5 mm collimation with two detector rows 0.2 reconstruction increment 1 mm table feed and rotation 1 s rotation time tube current 180 mAs with 120 kVp field of view, 9 cm), and all images (native and reformatted) displayed at a window center of800 HU and a window width of 4,000 HU. Despite the advent of more powerful scanners (32-64 slices) that allow a further improvement in speed and resolution along the z-axis, acquisition protocols reported in the literature remain substantially unchanged in terms of section thickness in respect to those proposed for four-slice scanners (Lane et al. 2006). 

The technical aspects of virtual endoscopy (VE) have been introduced in Chapter , to which the reader should refer. The application of VE to the study of the middle ear is quite simple, but requires, as for the other image processing methods, the availability of volumetric and high-resolution data. The optimal CT acquisition protocols have already been discussed. 

The introduction of 64-slice MDCT scanners opens a new phase for CT imaging, thanks to the improved spatial resolution on the longitudinal axis as well as the increase speed of acquisition. Since new acquisition protocols make routinely use of suh-millimeter collimation and suh-millimeter image reconstruction, a real volumetric approach to abdominal imaging is made possible. 

Fig. 2. Image acquisition and processing steps to determine the transport of ts-045-G to the plasma membrane. HeLa cells were transfected with siRNAs on LabTek arrays as they are described in Chapter 1 of this issne. The ts-045-G transport assay was carried out as described in protocol 1.1 as described earlier in this chapter. Images were acquired sequentially using a lOX objective on a Scan R system using filters to detect specifically DAPI stained nuclei (A), Cy3 stained ts-045-G at the plasma membrane (B), and CFP-tagged ts-045-G (C). Images DT were generated as described in protocol 1.2. earlier in this chapter. R in (G) is the ratio of ts-045-G at the plasma membrane (measured in H) to ts-045-G expressed in cells (measured in I). Resnlts for siRNAs targeting the COPI component /3-COP, the COPII component Sec31p, and a p24 related membrane protein p26 are shown. The valnes are the average of two independent experiments (Bar = 50 /tm).

Micro-CT appears a useful tool for scanning ex vivo, fixed mouse lungs with sufficient spatial resolution and tolerable levels of noise because there are no temporal constraints on image acquisition. There are no motion artifacts or fluid shifts which can occur with in situ lung scans. Thus, for instance, it is possible to use the 9 p,m pixel resolution protocol of the Skyscan 1076 scanner. Optimized protocols for fixed mouse lung with different spatial resolutions are also being developed. The basic characteristics of the 9 fim protocol are scanning time 120 min, no filter, 50 kV and 200 p.A. 

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