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In Western countries colorectal cancer is one of the leading causes of cancer-related mortality. In the European Union in 2002, 142,505 individuals died of this disease and in the USA 59,345 individuals (Globoscan 2002). Most colorectal cancers are thought to develop from adenomas through the so-called adenoma-carcinoma sequence. Despite improvements in the treatment of colorectal cancer, mortality is not decreasing noticeably. The most important reason for this is the presence of extensive disease at the time of diagnosis. Prevention and early detection of colorectal cancer and precursors of colorectal cancer (adenomatous polyps) by screening is possible and at this moment seems to be the only way to substantially reduce the incidence and mortality of colorectal cancer (Pignone et al. 2002). [ABSTRACT FROM AUTHOR]

Radiation risks based on biology and physics have been covered in previous chapters and are, of course, also valid for children. In the same way, clinical approaches to dose optimization and reduction are similar in paediatric and adult CT examinations (Huda et al. 2000). This chapter will not repeat what has been said but concentrate on the fact that children are not just adults with smaller dimensions, thus it will rather point out what is different in children. [ABSTRACT FROM AUTHOR]

Computed tomography fluoroscopy (CTF) is a technique that provides the physician immediate feedback via the reconstruction and display of CT images in real time and overcomes the classic limitations of ultrasound imaging and conventional fluoroscopy. It matches the advantages of CT quality images to be matched with the speed of fluoroscopic guidance. CTF images: (1) have a wide dynamic range for imaging air, soft tissue and bone, (2) do not superimpose anatomical structures in the same way as conventional fluoroscopy does, and (3) they provide acceptable image quality relatively unaffected by the patient's breathing and motion (Kato et al. 1996; Froelich et al. 1998; Nickoloff et al. 2000). These characteristics allow immediate correction for the depth and direction of a needle during a percutaneous procedure. The obvious benefits of obtaining CT images in real time has made CTF a popular image guiding tool for various types of non-vascular and therapeutic interventions. [ABSTRACT FROM AUTHOR]

Since its introduction in the 1970s, computerized tomography (CT) has played an important role in the diagnosis of musculoskeletal disorders. It rapidly became the examination of choice for the diagnosis of disc herniation, fractures, bone tumours and some developmental abnormalities. Although the image quality was altered by streak artefact associated with medical devices, CT was also indicated in postoperative imaging (Blum et al. 2000; Iochum et al. 2001; Cotten et al. 2002; Fayad et al. 2005a, 2005b). [ABSTRACT FROM AUTHOR]

The radiation dose is becoming a major issue for contrast-enhanced cardiac CT (coronary CT angiography), because the radiation level associated with ECG-gated acquisition is generally higher than that with other CT acquisitions. However, multiphasic acquisitions of other organs (for example liver) may also be associated with a comparable or even higher total radiation, so this large radiation dose is not specific to cardiac CT. [ABSTRACT FROM AUTHOR]

Computed tomography is nowadays widely used in abdominal imaging in various circumstances including acute abdominal pain. This use is explained by the fact that this technique is highly reproducible, very rapid, highly sensitive and specific, quite easy to perform, and it causes little discomfort to the patient. With multi-detector row CT (MDCT) scanners, rapid volume acquisition became possible and examination of the whole abdomen is more and more frequently performed as a screening test in patients suspected of abdominal disorder. Such examinations of the whole abdomen are justified by the ability to detect alternative and/or additional diagnoses. However, since the abdomen contains sensitive organs, the radiation dose delivered to patients becomes a particular concern, especially in young patients and in those with chronic diseases who undergo repeated CT studies. [ABSTRACT FROM AUTHOR]

Since the late 1980s, helical computed tomography (CT) has revolutionized diagnostic imaging of the chest. Single-detector CT scanners (SDCT) and, more recently, multi-detector CT scanners (MDCT) have markedly increased the number of indications of CT. As a result, the number of CT examinations performed has increased dramatically, as have the average scanned volume per patient and the number of acquisitions per examination. The subsequent increase in collective radiation dose has been of concern to radiologists, medical physicists and governmental regulatory authorities and it has been suggested that the radiation dose used for CT was excessive (Rogers 2001a, b). [ABSTRACT FROM AUTHOR]

Since its introduction in the 1970s, CT has played an increasingly important role in the imaging diagnosis of a variety of disorders. This is especially true in the field of neuroradiology, where CT made direct visualization of neurological anatomy possible for the first time, thereby revolutionizing diagnostic imaging. [ABSTRACT FROM AUTHOR]

Although the contribution of CT scanning to radiation dose was recognized prior to the introduction of multidetector-row CT scanners, ever expanding applications of multidetector-row CT scanning in patient care and, of late, use of CT for screening have heightened concerns and awareness of radiation- induced cancer from CT radiation dose and prompted the development of strategies and techniques for dose reduction (Frush 2003; Kalra et al. 2004a; Tack and Gevenois 2004). Technological innovations for dose reduction and optimization include pre-patient beam collimation and beamshaping filters as well as automatic exposure control techniques (Kalra et al. 2004b). To obtain appropriate benefits of these techniques in terms of dose reduction without compromising image quality, it is important to appropriately center the patients in the scanner gantry isocenter (Kalra et al. 2004b). [ABSTRACT FROM AUTHOR]

William Shakespeare might have accidentally explained the premise for development of automatic exposure control (AEC) techniques, although Henry Miller might have summarized the issues related to the heterogeneous nomenclature of these techniques! [ABSTRACT FROM AUTHOR]

The danger of ionizing radiation is related to the potential long-term risk of carcinogenesis. In Chapters. 1 and 2 of this book, Chadwick and Cohen have detailed how this risk is evaluated and considered in the field of low-level radiation in which diagnostic imaging (including CT) in comprised. The linear no threshold (LNT) theory of carcinogenesis is based on the risk of hereditary mutations deriving from cellular effects in germ cells. This theory considers that the cancer risk is linearly proportional to the dose at high doses as well as at low doses, from zero dose up. On the other hand, failure of the LNT theory is based on series of investigations showing that there is substantial evidence that low-level radiation does not have any carcinogenic effect and may even be protective against cancer, a view known as "hormesis". [ABSTRACT FROM AUTHOR]

Over the years a lot of surveys have been carried out trying to estimate not only the collective dose of computed tomography (CT) examinations but also the effective dose for specific scan regions. Only a few surveys of large sample size have been carried out [UK 1999, 2001 and 2003 National Radiological Protection Board 1999; Hart and Wall 2001; Shrimpton et al. 2003); Germany 1992-1995, 1999, 2002 (Bernhardt et al. 1995; Galanski et al. 2001; Brix et al. 2003); Switzerland 1998 (Aroua et al. 1998); and Austria 2000 (Nowotny)] while a larger number of surveys with smaller sample sizes can be found in the literature. The later ones were often focused on either a limited number of scanners or a small number of scanner sites (e.g. Greece, Italy, Wales, USA). These small surveys will always contain biased data because they are not representative of all scanners and sites (Szendrö et al. 1995; Olerud 1997, 2003; van Unnik et al. 1997; Scheck et al. 1998; Shrimpton et al. 1998; Goddard and Al-Farsi 1999; Einarsson and Magnusson 2001; Hiles et al. 2001; Olerud et al. 2001; Tsapaki et al. 2001; Hatziioannou et al. 2003; Papadimitriou et al. 2003; Origgi et al. 2006). [ABSTRACT FROM AUTHOR]

It is commonly stated that "any radiation dose, no matter how small, can cause cancer." The basis for that statement is the linear no-threshold theory (LNT) of radiation carcinogenesis. According to LNT, if 1 Gy (100 rad) of exposure gives a cancer risk R, the risk from 0.01 Gy (1 rad) of exposure is R/100, the risk from 0.00001 Gy (1 mrad) is R/100,000, and so on. Thus the cancer risk is not zero regardless of how small the exposure. However, in recent years, a strong sentiment has developed in the community of radiation health scientists to regard risk estimates in the low-dose region based on LNT as being grossly exaggerated or completely negligible. For example, the 6000-member Health Physics Society, the principal organization for radiation protection scientists, issued a position paper (Health Physics Society 1996) stating "Below 10 rad ... risks of health effects are either too small to be observed or are non-existent." A similar position statement was issued by American Nuclear Society. [ABSTRACT FROM AUTHOR]

The exposure to radiation of patients undergoing computed tomography (CT) examinations is determined by two factors: equipment-related factors, i.e., design of the scanner with respect to dose efficiency, and application-related factors, i.e., the way in which the radiologist or the radiographer makes use of the scanner. In this chapter, the features and parameters influencing patient dose are outlined. First, however, a brief introduction on the dose descriptors applicable to CT is given. [ABSTRACT FROM AUTHOR]

The radiation doses received by patients undergoing diagnostic radiological examinations by means of computed tomography (CT) are generally in the order of 1-24 mSv (milliSieverts) per examination for adults (UNSCEAR 2000) and 2-6.5 mSv for children (Shrimpton 2003). These effective doses can be classified as low, although they are invariably larger than those observed using conventional diagnostic radiology. The immediate question that comes to mind is whether these low doses carry any risk for the patient. [ABSTRACT FROM AUTHOR]

The principles of protecting the subject undergoing investigation by radiation are clear and well known: it is the responsibility of all radiological services to ensure the information required for the clinical management of the patient is obtained with the lowest practicable exposure to radiation. Within this clear objective, however, medical investigation operates in a constantly changing scenario influenced by increasing knowledge of disease processes and advancing technological development. This syndrome ensures that as time passes differing objectives and concerns come to the fore. Over the past few years the emergence of multidetector computed tomography (MDCT) has posed new challenges in radiological protection, to the extent that some now claim that this represents today's greatest single challenge in clinical radiation protection. This book expounds the challenges posed by MDCT to scientists and physicians and in this chapter we provide an introduction to the main themes which are of concern. [ABSTRACT FROM AUTHOR]

In summary, the above-mentioned innovations help to establish a very high quality in MRI examinations of the liver. Each innovation alone, but particularly their combination, is of great value. Whereas the application of 3D sequences and navigator triggering is still confined to some sequences, parallel imaging is a universal technique to speed up the acquisition in all sequence types used for liver imaging at present. Moreover, the utilization of parallel imaging also allows increasing the spectrum of suitable sequences, as shown above with the example of diffusion-weighted EPI sequences. This outstanding and universal role of parallel imaging holds also true for the combination of parallel imaging with high-field MR systems. Future developments have to aim at new coil geometries and more refined algorithms, which might allow even higher acceleration factors also for transversally orientated acquisitions without the loss of image quality. This is of importance as this will remain the orientation of choice for liver imaging. [ABSTRACT FROM AUTHOR]

Transabdominal ultrasonography can be a useful alternative modality to EUS in the assessment of carcinoid or submucosal tumors. [ABSTRACT FROM AUTHOR]

Although influenced by the patients' constitution and the skill of the operator, transabdominal ultrasound can be a useful diagnostic tool for the evaluation of gastric cancer. [ABSTRACT FROM AUTHOR]

Sonography can diagnose diverticulosis with an accuracy of approximately 60%. Most diverticula present as echogenic protrusions in some cases they are hypoechogenic. In most cases, diverticulitis sonographically presents as peridiverticular inflammation. Often microperforations are present. The peridiverticular inflammation of the fat is primarily hyperechogenic, and in advanced cases is hypoechogenic. Performed by an experienced investigator, sonography shows results comparable to those of CT in diagnosing acute diverticulitis, and an accuracy of more than 90% can be reached. If complications, such as abscess formation or fistulas, are suspected, CT should be performed. In distal sigmoid localisation, transrectal examination provides high-resolution images with a high specificity. [ABSTRACT FROM AUTHOR]

Sonography is the first-line imaging method for diagnosing acute appendicitis. Experienced investigators have an accuracy of more than 90%. Sonography can diagnose many conservatively managed diseases. Sonography can reduce the high rate of false-positive clinical examinations concerning acute appendicitis. It has to be stated that exclusion of appendicitis can only be made sonographically if the normal appendix can be seen in its full length and/or other differential diagnoses can be depicted which explain the clinical symptoms. Mucoceles are rare cystoid lesions of the appendix. They exhibit a typical onion-skin-sign structure caused by mucus. In large mucoceles a tumour causes this lesion. [ABSTRACT FROM AUTHOR]

In summary, parallel-imaging techniques not only provide improved spatial and temporal resolution as well as the reduction of image artefacts, but also increase the diagnostic capabilities of magnetic resonance imaging through more comprehensive imaging protocols. This will allow a better evaluation of systemic diseases as well as more consistent detection and communication of pathologic findings. [ABSTRACT FROM AUTHOR]

Theoretical work on parallel RF transmission and recent experimental implementations on prototype systems indicate that parallel excitation has the potential to overcome critical obstacles to robust and routine human scanning at high field strength. As these developments are extended to 16- and 32-channel neuroimaging arrays, it seems likely that very-high-field human brain imaging will be possible with an essentially constant flip angle across the human head with RF pulse durations comparable to current slice-selective pulses. While most work has been concentrated on head-sized transmitters, the problem of B1 homogeneity in the torso becomes significant at lower B0 fields. Thus, the first clinical applications might be for body transmit coils at 3 T. Of course, intriguing research questions remain open in several areas, including optimal coil array designs that minimize element couplings and maximize spatial orthogonality of individual channels, the estimation and real-time monitoring of local SAR during simultaneous application of RF in excitation coil arrays, and the development of rapid and robust RF pulse designs that extend the current low-flip-angle domain to an arbitrary excitation angle, such as spin echoes, saturation, and inversions pulses. However, with continued active research in these areas, progress is likely to accelerate, and one can envision logical additions to the architecture of a current clinical scanner that readily accommodates the requirements of a general parallel RF excitation system. These include coil arrays optimized for parallel transmit and receive, modular blocks of RF synthesis and amplification with individual characterization of amplifier nonlinearities, subject-specific models of local SAR deposition for monitoring, and a rapid B1-estimation pre-scan that feeds fast RF-pulse-design software capable of incorporating E1 constraints. [ABSTRACT FROM AUTHOR]

In patients with pulmonary hypertension, MR imaging of the pulmonary circulation using the combination of MR perfusion imaging and MR angiography with parallel-imaging techniques provides a high diagnostic accuracy in differentiating PPH and CTEPH. Further larger-sample studies will be needed for validation. Besides improving temporal and spatial resolution of these techniques, also their required scan time can be substantially reduced from several minutes to even breath-holds. This allows the combined use of different morphologic and functional MRI techniques within a reasonable total scan time. MR angiography of the pulmonary vasculature can be complemented by additional functional measurements such as flow measurements and assessment of right-heart cardiac function. In the future, potential clinical applications of pulmonary MRI in the diagnosis of pulmonary hypertension could include ventilation imaging using oxygen, or quantitative assessment of pulmonary perfusion, enabling a truly comprehensive workup of PH using MRI alone. [ABSTRACT FROM AUTHOR]