Clinical protocol/data acquisition

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]. 

Optimal abdominal MDCT data acquisition for 3D evaluation is determined by the scanner available, clinical indication, choice of oral and IV contrast material, and knowledge of the risks of radiation. A list of the current NYU MDCT protocols for specific indications are listed at the end of this chapter. These protocols were developed to allow optimal CT data acquisition for both 2D and 3D data interpretation while trying to limit radiation dose to the patient. By obtaining thin section MDCT data, 3D data interpretation is facilitated by the use of isotropic voxels which enable both MPR and volume rendering to be performed. 

Pulsation of the aorta causes artifacts, especially in the aortic root and ascending aorta. ECG-triggered data acquisition helps to significantly reduce these artifacts and therefore plays an important role in the examination of unclear chest pain or thoracic aortic dissection (Fig. 23.1). Furthermore, this technique enables the evaluation of coronary arteries and can replace invasive clinical diagnostics in some cases. Flowever, detailed protocols of the thoracic aorta are normally based on protocols of coronary artery CT. Due to their specifications, they lead to longer acquisition times than those of standard protocols and do not properly visualize the abdominal aorta. This can be overcome by an ECG-gated acquisition of the thoracic aorta and a change to the standard protocol for the abdominal aorta. In order to achieve a sufficient contrast in the abdominal aorta, the time delay to modify the examination protocol should be minimized (Fig. 23.2). 

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... 

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