Spiral CT scanner

With the advent of spiral CT scanners, it has become possible for the first time to continuously scan an anatomic region without having to interrupt data acquisition. This new technique has therefore almost completely eliminated the problem of misregistration of small anatomic or abnormal structures [7]. Incremental CT,the predecessor of spiral CT,was limited in the diagnostic evaluation of round pulmonary lesions, focal liver lesions, and lymph nodes because this technique might either miss such lesions or depict them twice when the patient moved between acquisitions [8]. This is why protocols for incremental CT are not presented here. 

Table 13.3. Recommended parameters to obtain a VL using a single-slice spiral CT scanner ...

With the introduction of MDCT bi-, tri-, or even quadruple-phasic examinations of the liver can be combined into a thoraco-abdominal CT examination, without compromise with regard to spatial or temporal resolution. The acquisition of the liver with a 64-slice scanner for example only requires a few seconds, despite a submillimeter collimation. Even patients with a compromised general state of health are able to tolerate these breath-hold times. However, even on single-slice spiral CT scanners adequate image quality of the liver can be obtained. However, combination with thoracoabdominal examinations is not possible without compromises in temporal and spatial resolution. 

Early spiral-CT scanners (34) provided stacks of cross-sectional CT sections. However, the slices were separated in time. The DSR acquired all the slices simultaneously but cone-beam reconstructions required a prohibitive amount of computation time. Tomography slices in medical CT have, until recently, been generated from one-dimensional projections via fan-beam methods. 

However, the scanning time of a single-slice spiral CT scanner is too slow to obtain a pure arterial phase the result is a hybrid phase, with mixed arterial and portal venous enhancement (usually shces acquired first in the volume have a pure arterial enhancement whereas subsequent slices show portal dominant enhancement). 

According to the literature liver metastases are detected with spiral CT with a sensitivity ranging from 58% to 85% [31, 53, 56]. Data from single-row spiral CT and MDCT show that the optimal reconstructed slice thickness for reading CT examinations of the liver on transversal sections is in the range of 2.5 mm-5 mm [17, 57]. Since a reconstructed slice thickness of 2.5 mm is difficult to obtain without motion artifacts on single-row scanners, the use of... 

Many users of spiral and multislice CT scanners have switched from conventional image interpretation to primary digital interpretation on the monitor. The interactive options have numerous advantages... 

With conventional MR imaging techniques, lymph nodes are visualized vdien they have a size of at least 1.0-1.5 cm [10]. Optimized imaging techniques (body phased-array coil, 512 matrix, 3D acquisition) or state-of-the-art spiral or multislice CT scanners depict lymph nodes as small at about 3-5 mm [7,8]. These techniques usually allow good evaluation of the lymph nodes adjacent to the straight great vessels (Fig. 15.1). 

Patient data acquisition is based on spiral CT and the whole data processing part is optimized for it. MRI could be used instead of spiral CT, but is not implemented yet. For spiral CT, scanning multirow detector computed tomography is used in the past the detector used was a GE Lightspeed QXl Scanner (GE Systems, Milwaukee, Wl, USA), but recently there was an opportunity to use a Siemens Somatom Sensation (Siemens Medical System Inc., Forchheim, Germany). 

The introduction of multidetector row computed tomographic (MDCT) scanners in late 1998 opened a new era for CT in general and CTC in particular (Berland and Smith 1998). The use of multiple detector arrays along the z-axis offers substantial benefits related to anatomic coverage, scanning time and longitudinal spatial resolution compared with single-slice spiral CT (SSCT) (Beaulieu et al. 1998 Fenlon et al. 1999 Kara et al. 2001). 

Vascular emergencies play an important role amongst the various differential diagnoses for acute chest pain. Pulmonary embolism, acute aortic syndromes as well as acute coronary artery disease have to be considered.The latest scanner technology available (> 64-slice multi-detector-row spiral CT platforms) allows for a straight-forward work-up in the emergency situation. A dedicated triage based on a sophisticated clinical assessment, however, ist required. 

The trajectory of the focal spot with respect to the patient is approximately planar, whereas it is a spiral on a CT scanner. The trajectory does not cover a full rotation in FD-CT. 

In four-slice spiral CT the same acquired raw data set can be used to reconstruct two or more data sets of varying thickness. For this reason, it is important to distinguish between acquisition parameters, given as (NxSC/TF), and reconstruction parameters, expressed as (SW/Rl) (Cademartiri et al. 2003). With multislice scanners, two definitions of pitch factor are used, depending on whether a section (P =TF/SC) or total collimation of the detector array (P=TF/NxSC) is chosen as the reference (Prokop 2003c). 

Kalender W, Seissler W, Klotz E, Vock P (1990) Spiral volumetric CT with single-breath-hold technique, continuous transport and continuous scanner rotation. Radiology 176 181-183... 

With modern MDCT scanners, the indications for sequential CT scanning—as opposed to spiral scanning—are usually limited to dynamic protocols such as perfusion CT (PCT) and to sequential scans of the infratentorial brain or skull base. Sequential scanning can reduce beam hardening artefacts and overbeaming however, 3D-refomation options are limited. 

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