Detector rows

Figure 6 A multi-row detector array is used in a cone-beam system. In this case, the detector rows fall along circular arcs centered on the X-ray source s x, y coordinate values. Detectors of equal size therefore subtend equal angles with respect to the source. This characteristic and other system and data-analysis considerations often make curved detector rows more attractive than straight ones like those of Figures 3 and 4.

The primary deterrent to reducing the detector center-to-center distance for the structure presented above in US-A-4551629 is the required thickness of each silicon chip. If the chips are too thin, they will be very fragile, and will therefore be difficult to handle during fabrication of the modules. In US-A-4403238 (Irvine Sensors Corporation, USA, 06.09.83) the distance between adjacent detector rows can be less than the thickness of a given chip, by orienting the detector rows along lines which extend diagonally with respect to the planes in which the silicon chips extend. 

Fig. 18. Geometry of fan-beam coherent scatter computed tomography. A fan beam is used to illuminate one object slice. The central detector row (in the plane of the drawing) receives the transmitted radiation while the out-of-plane rows receive only scattered radiation. The coordinate represents the projection angle whereas...

The Radon transform permits reconstruction of a 2-D slice of an object from a complete set of its line integrals. Reconstruction is performed on a 3-D object array consisting of the two spatial coordinates (x, y) in the illuminated slice and one momentum transfer (or angular) coordinate, q. This has to be calculated from the distance of an object voxel (x, y) from the detector, d, and the vertical distance, a, of the corresponding detector pixel from the central detector row. From Eq. 13, the calculation of q for all object positions along a ray results in curved trajectories described by ... 

M. Hypervascular hepatocellular carcinoma detection with double arterial phase multi-detector row helical CT. Radiology 2001 218 763-767... 

Willmann, J.K., Weishaupt, D., Bdhm, T., Pfammatter, T., Seifert, B., Marincek, B., Bauerfeind, R Detection of submucosal gastric fundal varices with multi-detector row CT angiography. Gut 2003 52 886-892... 

In CT, typically an X-ray tube and a detector are rapidly rotated 360° around the patient (see Fig. 4.1). The acquisition time of an image is determined by the rotation time of the detectors and the X-ray tube, which ranges from 0.3 to 1 second. Modern CT scanners use a number (16-64) of detector rows, which allows the simultaneous measurement of multiple slices. Further reduction of the scan time can be achieved by faster rotation times. There-... 

With regard to MDCT radiation exposure, several factors must be weighed. There is up to a 4.5% loss of efficiency vs. single-detector row scanners due to absorption of radiation in the z-axis by septa between the detector rows [31]. However, with MDCT, most of the X-ray beam is utilized per rotation due to the increased number of detector rows, with less of a penumbra [31]. Subsequently, these effects balance and the dose efficiency of MDCT has been shown to be comparable to that of single-slice helical CT [31]. 

Coverage volume will continue to increase with enlarging detector arrays and improved technology. Cutting edge scanners with 320 detector rows offer the possibility of 16-cm coverage without the decreased temporal resolution required with shuttle-mode technique. However, some early clinical reports noted inferior image quality with 320-slice MDCT compared to 64-slice MDCT [83, 84]. 

Keyzer C, Tack D, Bohy P et al (2004) Acute appendicitis comparison of low-dose and standard-dose unenhanced multi-detector row CT. Radiology 232 164-172 Kimmey MB, Martin RW, Haggitt RC et al (1989) Histologic correlates of gastrointestinal ultrasound images. Gastroenterology 96 433-441... 

Computed tomography (CT) has developed dramatically with the introduction of multi-row detector technology. Especially the abdomen, where motion artifacts due to respiratory motion and bowel peristalsis are disturbing, benefits greatly from this technique. While scanners with 64 or more detector rows are still most common in large community or university hospitals, scanners with between 2 and 16 slices are widely available even in private practice or in small hospitals. With the introduction of multi-detector CT (MDCT) bi- or even tri-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... 

Haider MA, Amitai MM, Rappaport DC et al (2002) Multi-detector row helical CT in preoperative assessment of small (liver metastases is thinner collimation better Radiology 225 137-142... 

Keyzer C, Zalcman M, De Maertelaer V et al (2005) Comparison of US and unenhanced multi-detector row CT in patients suspected of having acute appendicitis. Radiology 236 527-534... 

In the future the need for flush aortography prior to and after embolization may be obviated, when the use of multi-detector row CT becomes more and more common. There are indications that the use of thin-section CT scanning reduces procedural time, as well as the potential iatrogenic risks of a selective search for ectopic bronchial or abnormal non-bron-chial systemic arteries [19]. 

Remy-Jardin M, Bouaziz N, Dumont P, Brillet PY, Bruzzi J, Remy J (2004) Bronchial and nonbronchial systemic arteries at multi-detector row CT angiography comparison with conventional angiography. Radiology 233 741-749... 

Trauma is one of the most common reasons for a child s attendance in the emergency department. Plain radiographs may remain the primary imaging modality following suspected skeletal injury, but with the advent of first single detector CT (SDCT) and now multi-detector row CT (MDCT) scanners, the role of CT in skeletal trauma has continued to develop. 

Beam collimation and table movement together (i.e. pitch) determine the volume of tissue irradiated per gantry rotation, whereas section collimation determines the minimal slice (also known as section) thickness that can be reconstructed from an examination s raw data. That is, the narrowest selected reconstructed slice thickness available will equal the selected size of the detector elements (Dalrymple et al. 2005). Section collimation may also be referred to as (effective) detector (row) thickness. The term detector configuration merely couples together the value selected for the section collimation with the number of detector elements. For example 4 x 1.25 refers to a four- channel scanner acquiring four channels of data 1.25 mm thick. Similarly, 16 x 0.625 refers to 16 channels of data 0.625 mm thick obtained on a 16-channel scanner. From this information and the equation for pitch, it can be seen that detector configuration is numerically equal to the beam collimation (Rydberg et al. 2003 Saini 2004). 

Parameters are based on GE single and multi-detector row scanners. 

John SD (1999) Trends in pediatric emergency imaging. Radiol Clin North Am 37 995-1034 Kalra MK, Maher MM, Kamath RS et al (2004a) Sixteen-detector row CT of abdomen and pelvis study for optimization of Z-axis modulation technique performed in 153 patients. Radiology 233 241-249 Kalra MK, Maher MM, Toth TL et al (2004b) Comparison of Z-axis automatic tube current modulation technique with fixed tube current CT scanning of abdomen and pelvis. Radiology 232 347-353... 

Rydberg J, Liang Y, Teague SD (2003) Fundamentals of multichannel CT. Radiol Clin North Am 41 465-474 Saini S (2004) Multi-detector row CT principles and practice for abdominal applications. Radiology 233 323-327 Salamipour H, Jimenez RM, Brec SL et al (2005) Multidetector row CT in pediatric musculoskeletal imaging. Pediatr Radiol 35 555-564... 

Hogan GJ, Mirvis SE, Shanmuganathan K, et al.(2005) Exclusion of unstable cervical spine injury in obtunded patients with blunt trauma is MR imaging needed when multi-detector row CT findings are normal Radiology 237 106-113... 

When considering an abdominal multi-detector-row CT (MDCT) protocol to enable optimal diagnostic capability, there are several important factors that need to be considered. Most importantly, what is the clinical indication for the study This will enable the radiologist to tailor the CT protocol appropriately to obtain the diagnostic information requested. Appropriate tailoring of the protocol requires consideration of ... 

McNulty NJ, Francis IR, Platt JF, Cohan RH, Korobkin M, Gebremariam A (2001) Multi-detector row helical CT of the pancreas effect of contrast-enhanced multiphasic imaging on enhancement of the pancreas, peripancreatic vasculature, and pancreatic adenocarcinoma. Radiology 220 97-102... 

Prokesch RW, Chow LC, Beaulieu CF, Bammer R, Jeffrey RB Jr (2002) Isoattenuating pancreatic adenocarcinoma at multi-detector row CT secondary signs. Radiology 224 764-768... 

Orbach DB, Pramanik BK, Lee J, Maldonado TS, Riles T, Grossman RI (2006) Carotid artery stent implantation evaluation with multi-detector row CT angiography and virtual angioscopy-initial experience. Radiology 238 309-320... 

Beyer T, Rosenbaum S, Veit P et al. (2005) Respiration artifacts in whole-body (18)F-FDG PET/CT studies with combined PET/CT tomographs employing spiral CT technology with 1 to 16 detector rows. Eur J Nucl Med Mol Imaging 32(12) 1429-1439... 

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). 

Beigelman-Aubry C, Hill C, Guibal A, Savatovsky J, Grenier PA (2005) Multi-detector row CT and postprocessing techniques in the assessment of diffuse lung disease. Radiographics 25(6) 1639-1652... 

Almost every year, new CT scanners are introduced, allowing investigation of any part of the body with the highest spatial and temporal resolution within the shortest scan time. CT angiography performed with multi-detector-row CT (MDCT) and dedicated contrast protocols visualize even the smallest of vessels in the periphery of any vascular tree. Coronary arteries are of particular challenge for imaging by CT because of their small size and their continuous rapid movement. With the newest MDCT scanners, however, any vascular territory, including the coronary arteries, is now assessable with detailed anatomic (Achenbach et al. 2006). 

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