Application Of Computed Tomography Research Articles

Toward Clinical X-ray Phase-Contrast CT

X-ray computed tomography (CT) using phase contrast can provide images with greatly enhanced soft-tissue contrast in comparison to conventional attenuation-based CT. We report on the first scan of a human specimen recorded with a phase-contrast CT system based on an x-ray grating interferometer and a conventional x-ray tube source. Feasibility and potential applications of preclinical and clinical phase-contrast CT are discussed. A hand of an infant was scanned ex vivo at 40 kVp tube voltage. The simultaneously recorded attenuation and phase-contrast CT images were quantitatively compared with each other, by introducing a specific Hounsfield unit for phase-contrast imaging. We observe significantly enhanced soft-tissue contrast in the phase images, when compared with the attenuation data. Particularly, tendons and ligaments appear with strongly increased contrast-to-noise ratio. Our results demonstrate the huge potential of phase-contrast CT for clinical investigations of human specimens and, potentially, of humans. Because the applied technique works efficiently with conventional x-ray tubes and detectors, it is suitable for the realization of preclinical and clinical phase-contrast CT systems.

Perfusion CT in solid body-tumours part II. Clinical applications and future development

Perfusion computed tomography (CTP) has shown great potential in diagnosing tumours and evaluating and predicting treatment response and has been the subject of numerous experimental and clinical studies. Its increasing availability and simplicity allow it to be performed alongside morphological imaging to complete the evaluation of neoplastic lesions. The aim of this paper is to describe our personal experience and review the literature on the applications of CTP in tumours of different body regions, with particular regard to fields of development for new research. Increased clinical application is desirable, especially in relation to a wider use of antiangiogenic drugs. Additional and ideally multicentre studies are necessary to define the role of this technique.

Multi-energy image stack fusion in computed tomography

In the past years computed tomography (CT) was adopted to manufacturing metrology rapidly. Due to the main benefit that lies in the volumetric model generated for each measurement object, many application possibilities from non-destructive testing to coordinate measurements of inner and outer features are possible in much shorter time without destroying the sample. However, some limitations apply to the application of CT. First, it is not possible to measure objects of high aspect ratios (ratio width to thickness) as the changing material thickness influences the remaining intensity after the radiation passed through the workpiece. Secondly, parts consisting of different absorbing materials cannot be measured as only the high absorbing components are acquired with a good signal-to-noise ratio, i.e. with high accuracy and low measurement uncertainty. As high radiation energies are necessary to assure remaining intensities greater than zero in the radiographs, low absorbing components are outshone and not visible after reconstruction. The fusion of multi-energy stacks has been developed to deal with these issues. The approach and first measurement results are shown here.

Clinical experience of 71 cases of congenital middle ear cholesteatoma

Conclusions. As congenital middle ear cholesteatoma (CMC) is a different disease entity from acquired cholesteatoma, early diagnosis is important for good treatment results. Preoperative computed tomography (CT) imaging is a useful modality for both evaluation of the extent of the disease and selection of appropriate surgical methods. Some modification should be considered based on the findings of the actual operative field for complete removal of CMC. Objectives. To present the results of surgical treatment of 71 cases of CMC and investigate the applicability of preoperative CT for the treatment of CMC. Patients and methods. A retrospective study over an 11-year period was performed. The presenting symptoms, tympanic membrane findings, surgical findings, methods, and results were investigated retrospectively. Results. CMC was found incidentally in 38 cases (53.5%). A whitish mass medial to the tympanic membrane was observed in 62 cases (87%). Postoperative air–bone gap changes were not statistically significant. There was no predominance of localized lesions of the middle ear. The recurrence rate was 9.9% (seven cases), and higher in open type. Staging by CT and surgical staging matched in 70.4%. Positive predictive value for mastoid involvement of CT staging was 72.7%, with sensitivity and specificity of 68.6% and 87.5%, respectively.

Patient dose considerations in computed tomography examinations.

Ionizing radiation is extensively used in medicine and its contribution to both diagnosis and therapy is undisputable. However, the use of ionizing radiation also involves a certain risk since it may cause damage to tissues and organs and trigger carcinogenesis. Computed tomography (CT) is currently one of the major contributors to the collective population radiation dose both because it is a relatively high dose examination and an increasing number of people are subjected to CT examinations many times during their lifetime. The evolution of CT scanner technology has greatly increased the clinical applications of CT and its availability throughout the world and made it a routine rather than a specialized examination. With the modern multislice CT scanners, fast volume scanning of the whole human body within less than 1 min is now feasible. Two dimensional images of superb quality can be reconstructed in every possible plane with respect to the patient axis (e.g. axial, sagital and coronal). Furthermore, three-dimensional images of all anatomic structures and organs can be produced with only minimal additional effort (e.g. skeleton, tracheobronchial tree, gastrointestinal system and cardiovascular system). All these applications, which are diagnostically valuable, also involve a significant radiation risk. Therefore, all medical professionals involved with CT, either as referring or examining medical doctors must be aware of the risks involved before they decide to prescribe or perform CT examinations. Ultimately, the final decision concerning justification for a prescribed CT examination lies upon the radiologist. In this paper, we summarize the basic information concerning the detrimental effects of ionizing radiation, as well as the CT dosimetry background. Furthermore, after a brief summary of the evolution of CT scanning, the current CT scanner technology and its special features with respect to patient doses are given in detail. Some numerical data is also given in order to comprehend the magnitude of the potential radiation risk involved in comparison with risk from exposure to natural background radiation levels.

The development of a guidance level for patient dose for CT examinations in Korea

The primary goal of this study was to analyse the state of patient doses in the field of computed tomography (CT) examinations in the Republic of Korea. All survey data including the CT applications and patient dose details were obtained from general hospitals registered in the Korean Hospital Association. The systematic analysis of the patient dose survey gives target values of the weighted computed tomography dose index (CTDI(w)) and the dose-length product (DLP). The targeted CTDI(w) values were 69, 69, 31, 19, 44, 25, 24, 20, 2, 19 and 19 mGy for the brain non-contrast enhancement (BNCE), brain contrast enhancement (BCE), neck, chest, spine, liver, pancreas, stomach, kidneys, abdomen routine and abdomen trauma protocols, respectively. The targeted DLP values were 1056, 2112, 762, 1234, 1338, 2794, 2742, 2378, 2836, 1844 and 1939 mGy cm for the BNCE, BCE, neck, chest, spine, liver, pancreas, stomach, kidneys, abdomen routine and abdomen trauma protocols, respectively. Comparing with the EUR recommendation, especially in the DLP, the adjustment of the total scan phase frequency and the shortening of the scan phase in each scan phase are needed to reduce the patients radiation exposure to international standards.

Perfusion computed tomography could be a new tool for single-session imaging of ureteric obstructive pathology: an experimental study in rats

Background/Purpose Perfusion imaging redefines computed tomography (CT) as a technique that can now depict vascular physiology in addition to detailed anatomy. The major clinical applications of perfusion CT are in acute stroke and oncology. Currently, there are very limited data on the application of perfusion CT in urology. The aim of the present study is to investigate the potential value of perfusion CT in anatomic and functional evaluation of obstruction in a single session on experimental hydronephrosis model in rats. Thus, we evaluate the perfusion CT in a new clinical application. Methods Twenty-eight rats were randomly allocated into 4 groups each consisting of 7 rats. At the third week of experimental intervention, postoperative renogram curves and perfusion parameters of the right kidneys' cortex and pelvis were assessed by CT. The right ureter was sutured as proximal complete obstruction in group 1, as distal complete obstruction in group 2, and as proximal partial obstruction in group 3. Group 4 served as the sham control group. Computed tomography was performed with single-slice tomography. Dynamic examination was performed with the help of perfusion software through contrast-enhanced tomography examination. Results In all study groups, the aorta time/density curves showed a rapid increase after a rapid decrease, and the duration to reach peak concentration in the normal kidney cortex was observed to be later than the aorta as expected. In groups 1, 2, and 3, the duration to reach peak concentration lengthened and the peak concentration values decreased. The time/density curves gradually increased as a result of the accumulation of the contrast agent in the pelvis, and a peak was observed at the end of the procedure in all study groups. In groups 1, 2, and 3, a statistically significant decrease ( P = .01, P = .01, and P = .01, respectively) was observed in the peak concentration values of the contrast agent in comparison to group 4. The flow and blood volume values gradually decreased as the grade of the obstruction increased and the localization of the obstruction or grade of obstruction moved closer to the kidney. Conclusion In conclusion, perfusion CT technique, performed in a single session, is a useful method for anatomic visualization, together with functional evaluation, in the diagnosis of ureteric obstructive pathology of experimental hydronephrosis model.

Web review: Contrast media in radiology and imaging

Few web-based sites related to contrast media in radiology and imaging, available at the moment, are reviewed below. Introduction to Intravenous Radiographic Contrast is a concise summary of the subject by Romell Dhadha. Featured as a part of the Department of Radiology Short Clerkship: Lectures at University of Iowa, the material is available at http://www.radiology.uiowa.edu/Radshortclerkship/RadShortClkship/LectureNotes/Dhada.htm. A Simple Guide to the Basics of Contrast Media is available in the form of Guide notes at http://www.e-radiography.net/contrast_media/contrast_media_introduction.htm. The material includes iodinated intravascular contrast agents, barium sulfate, computerized tomography (CT) contrast agents, biliary contrast agents and reactions, allergic emergencies. From eMedicine, comprehensive educative material on radiographic iodinated contrast media is obtainable at http://www.emedicine.com/radio/byname/contrast-medium-reactions-recognition-and-treatment.htm. The webportal Chest Xray.com deals concisely with radiology contrast at http://www.chestx-ray.com/Practice/Contrast.html. The following sections are covered: general, non-ionic vs ionic, risk factors, severity of reactions, renal toxicity, screening creatinine and treatment. Incidentally, the portal chest Xray.com at http://www.chestx-ray.com/ covers areas related to research, education, practice and resources. Contrast Media in Diagnostic Radiology from the Textbook of Radiology at http://www.medcyclopaedia.com/library/radiology/chapter07.aspx is an up-to-date feature from Medcyclopaedia™. Medcyclopaedia™ is a “unique combination of a scientific library and a handy toolbox on the internet.” In addition, the site features the complete online edition of The Encyclopaedia of Medical Imaging, the complete online edition of A Global Textbook of Radiology, GE Healthcare's Expanded Medical Imaging Glossary, clinical cases for training purposes and a complete e-learning solution in normal imaging anatomy. A Symposium on Ultrasound Contrast for Radiological Diagnosis titled Bubbles in Radiology - The State of the Art is available at http://www.sunnybrook.utoronto.ca/bubble/. The site requires a mandatory registration. Additionally, ‘A Handbook of Contrast Echocardiography’ authored by Harald Becher and Peter N Burns is available at http://www.sunnybrook.utoronto.ca/EchoHandbook/. Within this, there is an Interactive Glossary of Contrast Ultrasound at http://www.sunnybrook.utoronto.ca/EchoHandbook/bookindex.htm. Controversies and Consensus in Imaging and Interventions is a journal for medical imaging professionals, focusing on current issues in radiology, imaging and interventional radiology/cardiology and CT radiology. This website, sponsored by an educational grant from GE Healthcare, has a section on contrast media that is available at http://www.c2i2.org/contrast_media.asp. An educative supplement on Issues in Contrast and CT Angiography with Multislice CT is featured in Applied Radiology (Mar 2002), accessible at http://www.appliedradiology.com/backissues/issue.asp?ID=71, after a compulsory registration. The material covers important topics such as optimizing contrast use in multislice CT, fast CT in neurological imaging: contrast issues, contrast multiplies cardiac CT applications, CTA of extremities: new approaches to scanning, contrast use, new contrast administration protocols: safety considerations. A panel discussion is also available at the end. Guidelines and manuals on the use of contrast media in radiology are issued periodically from reputed professional bodies. Currently available comprehensive references include American College of Radiology Contrast Manual on Contrast Media version 6/2008, which is available at http://www.acr.org/SecondaryMainMenuCategories/quality_safety/contrast_manual.aspx. ACR Practice Guideline for the Use of Intravascular Contrast Media, which is accessible at http://www.acr.org/s_acr/bin.asp?CID=541andDID=12241andDOC=FILE.PDF. European Society of Urogenital Radiology (ESUR) Guidelines on Contrast Media, available from http://www.esur.org/fileadmin/Guidelines/ESUR_2007_Guideline_6_Kern_Ubersicht.pdf. Royal College of Radiology Standards for Iodinated Intravascular Contrast Agent Administration to Adult Patient, available from http://www.rcr.ac.uk/docs/radiology/pdf/IVcontrastPrintFinal.pdf. Review Articles/Citations on Contrast media in Radiology: There are numerous articles on contrast media in radiology available from various journals. From these, a handy ‘must read’ list of review articles on this subject, published in recent times and available online, is given below in Table 1. Table 1 Review articles/citations on contrast media in radiology

Inverse geometry for grating-based x-ray phase-contrast imaging

Phase-contrast imaging using conventional polychromatic x-ray sources and grating interferometers has been developed and demonstrated for x-ray energies up to 60 keV. Here, we conduct an analysis of possible grating configurations for this technique and present further geometrical arrangements not considered so far. An inverse interferometer geometry is investigated that offers significant advantages for grating fabrication and for the application of the method in computed tomography (CT) scanners. We derive and measure the interferometer’s angular sensitivity for both the inverse and the conventional configuration as a function of the sample position. Thereby, we show that both arrangements are equally sensitive and that the highest sensitivity is obtained, when the investigated object is close to the interferometer’s phase grating. We also discuss the question whether the sample should be placed in front of or behind the phase grating. For CT applications, we propose an inverse geometry with the sample position behind the phase grating.

Grundlagen der Flachdetektor-CT (FD-CT)

Flat detectors (FDs) have been developed for use in radiography and fluoroscopy to replace standard X-ray film, film-screen combinations and image intensifiers (II). In comparison to X-ray film and II, FD technology offers higher dynamic range, dose reduction, fast digital readout and the possibility for dynamic acquisitions of image series, yet keeping to a compact design. It appeared logical to employ FD designs also for computed tomography (CT) imaging. FDCT has meanwhile become widely accepted for interventional and intra-operative imaging using C-arm systems. Additionally, the introduction of FD technology was a milestone for soft-tissue CT imaging in the interventional suite which was not possible with II systems in the past. This review focuses on technical and performance issues of FD technology and its wide range of applications for CT imaging. FDCT is not aimed at challenging standard clinical CT as regards to the typical diagnostic examinations, but it has already proven unique for a number of dedicated CT applications offering distinct practical advantages, above all the availability of immediate CT imaging during an intervention.

A Prospective Validation of a Current Practice: The Detection of Extremity Vascular Injury With CT Angiography

Arteriography is the current "gold standard" for the detection of extremity vascular injuries. Less invasive than operative exploration, conventional arteriography (CA) still has a 1% to 3% risk of morbidity and may delay definitive repair. Recent improvements in computed tomography (CT) technology has since broadened the application of CT to include the diagnosis of cervical, thoracic, and now extremity vascular injury. We hypothesized that CT angiography (CTA) provides equivalent injury detection compared with the more invasive CA, but is more rapidly completed and more cost effective. A prospective evaluation of patients, ages 18 to 50, with potential extremity vascular injuries was performed during 2006-2007. Ankle-brachial indices (ABI) of injured extremities were measured on presentation in all patients without hard signs of vascular injury. Patients whose injured extremity ABI was <0.9 were enrolled and underwent CTA followed by either CA or operative exploration if CTA findings were limb threatening. Interventionalists were blinded to CTA findings before performing and reading CAs. Twenty-one patients (mean age, 26.1 +/- 7.1 years) had 22 extremity CTAs after gunshot (82%), stab (9%), or pedestrian struck by automobile (9%) injuries to either upper (32%) or lower (68%) extremities. Eleven of 22 (50%) extremities had associated orthopedic injuries while the mean ABI of the study population was 0.72 +/- 0.21. Twenty-one of 22 (96%) CTAs were diagnostic and all CTAs were confirmed by either CA alone (n = 18), operative exploration (n = 2), or both CA and operative exploration (n = 2). Diagnostic CTAs had 100% sensitivity and specificity for clinically relevant vascular injury detection. Unlike rapidly obtained CTA, CA required 131 +/- 61 minutes (mean +/- SD) to complete. In our center, CTA saves $12,922 in patient charges and $1,166 in hospital costs per extremity when compared with CA. With acceptable injury detection, rapid availability, and a favorable cost profile, our results suggest that CTA may replace CA as the diagnostic study of choice for vascular injuries of the extremities.

Applications of computed tomography and magnetic resonance imaging in percutaneous ablation therapy for atrial fibrillation

Percutaneous catheter ablation is an established therapy for symptomatic drug-refractory atrial fibrillation (AF). Accurate delineation of relevant anatomy is critical but often challenging and limited in traditional technologies such as intra-procedural fluoroscopy. There has been an increased interest in non-invasive three-dimensional imaging technologies, especially computed tomography (CT) and magnetic resonance imaging (MRI), as useful tools for patients undergoing AF ablation. Here, we review applications of CT and MRI before, during, and after AF ablation and highlight areas for future research.

TU‐A‐213A‐01: CT Clinical Perspective: Challenges and the Impact of Future Technology Developments

Computed tomography is not the most frequent radiologic imaging procedure, but is arguably the most important in terms of clinical impact. CT is used extensively for emergencies, cardiovascular, pulmonary, gastrointestinal, endocrine, neurological, orthopedic and other applications — often as the first and only imaging procedure needed for diagnosis. The chances are very high that a patient will have a CT scan in the emergency department, as an outpatient or as an inpatient for a multitude of indications — pain, trauma, suspected infection or malignancy, and frequently to investigate symptoms such as pain, or to answer a question raised by another abnormal test, such as an EKG abnormality or ultrasound finding.Despite the universality of CT in hospitals and clinics as well as free‐standing imaging centers, the technology continues to evolve with greater coverage, faster acquisition and multienergy sources or detectors. Multimodality scanners based on CT incorporate PET/SPECT and in the future, MRI to combine morphologic and functional imaging.The most demanding imaging applications are cardiovascular, where complex motion and small morphologic features coexist, so imaging methods that are very satisfactory elsewhere in the body may not be successful. Clinical CT scanning consists of administering toxic materials, e.g., contrast media, often monitoring the EKG and illuminating the body with high brightness x‐rays. Larger area detectors and higher acquisition rates are welcome improvements, but don't solve all of the problems encountered with scan variability due to respiratory, random body, and cardiac motion, especially in a spectrum of patients from infant to massively obese adult sizes (&lt; 1 kg to 250 kg or more). The challenges and pitfalls in CT and multimodality imaging will be delineated and evaluated relative to current and future technology.Learning Objectives:1. The role of x‐ray computed tomography (CT) in clinical medicine is central to diagnostic radiology and its functions as a hospital‐based department and service to outpatients.2. CT technology developments, including wide area coverage multirow detector scanners, dual energy acquisition systems, visualization and post‐processing introduce changes in CT applications and utilization.3. The limitations of a single modality, such as CT, can be overcome by integrating complementary instrumentation, especially PET/SPECT, MRI and others (such as ultrasound and fluoroscopy) to provide simultaneous morphologic and functional imaging capabilities.

Virtual experimentation of beam hardening effect in X-ray CT measurement of multiphase flow

A virtual experimentation combining computational fluid dynamics (CFD) and computed tomography (CT) simulations was presented to evaluate the beam hardening effect in the CT application to multiphase flow measurement. A semi-industrial scale circulating fluidized bed (CFB) reactor was simulated with a multiscale CFD approach, and its computed flow fields was taken as the dynamic phantom for CT. By this means, a 3rd generation X-ray CT with different filter parameters was simulated. Since the computed flow fields can be manipulated in detail and reproduced at will, this virtual approach enables quantitative evaluation of the beam hardening effect and helps establish the optimal filter parameters for CT measurement of multiphase flow.

Electrical crosstalk in front-illuminated photodiode array with different guard ring designs for medical CT applications

Abstract This paper presents electrical crosstalk studies on front-illuminated photodiode arrays for medical computed tomography (CT) applications. Crosstalk is an important factor to the system noise and image quality. The electrical crosstalk depends on silicon substrate properties and photodiode structures. The photodiode samples employed in this paper are planar processed on high-resistivity n-type silicon substrate, resulting in a p+/n−/n+ diode structure. Two types of guard ring structures are designed and applied to the same geometry of two-dimensional photodiode arrays. One structure is an n guard ring in the gap area between pixels, and the other structure is an additional p+ guard ring around each pixel together with the n guard ring. A 10 μm light spot with wavelength of 525 nm is used to scan across the surface of the photodiode array in the electrical crosstalk measurements. The electrical currents of two neighbor pixels are measured and the results are compared between two guard ring designs. The design with the p+ guard ring structure gives better electrical crosstalk suppression. Moreover, the measurement results show much smaller influence on surrounding pixels with the p+ guard ring structure in the case of disconnected pixel. Besides the electrical crosstalk, the light sensitivity within the gap area is also discussed between two guard ring designs.

Imageology and histology to characterize tissue engineering repair of bone defects in rabbits

Objective To evaluate the effects of imageology and histology in characterizing tissue engineering repair of bone defects in rabbits. Methods The autologous bone marrow stroma cells (BMSCs) were obtained from the rabbits and cultured in vitro. After proliferation, the cells were incubated together with true bone ceramic (TBC) for 1 week, which were then imbedded into the 12 mm defects to repair the radius. X-ray and computer tomography (CT) exams and three-dimensional reconstruction were performed at 4, 8 and 12 weeks postoperatively for morphological observation before histological examination of the cells. Results After engineering repair, bone formation completed gradually and the defects of the bone were repaired. At 12 weeks postoperatively, X-ray and CT showed that the fracture lines disappeared completely, and the density of the engineering bone was similar to that of the normal radius. The smooth repaired bone grew into the normal radius. Histological examination showed regular arrangement of the mature bone trabecula and architecture, formation of the lamellar cortical bone. and partial degradation of the framework. Conclusion Combined application of radiography, CT, three-dimensional reconstruction and histology is a scientific and reliable method for characterization of tissue engineering repair of bone defects. Key words: Tissue engineering; Bone defect; Histology

Dual filtered backprojection for micro-rotation confocal microscopy

Micro-rotation confocal microscopy is a novel optical imaging technique which employs dielectric fields to trap and rotate individual cells to facilitate 3D fluorescence imaging using a confocal microscope. In contrast to computed tomography (CT) where an image can be modelled as parallel projection of an object, the ideal confocal image is recorded as a central slice of the object corresponding to the focal plane. In CT, the projection images and the 3D object are related by the Fourier slice theorem which states that the Fourier transform of a CT image is equal to the central slice of the Fourier transform of the 3D object. In the micro-rotation application, we have a dual form of this setting, i.e. the Fourier transform of the confocal image equals the parallel projection of the Fourier transform of the 3D object. Based on the observed duality, we present here the dual of the classical filtered back projection (FBP) algorithm and apply it in micro-rotation confocal imaging. Our experiments on real data demonstrate that the proposed method is a fast and reliable algorithm for the micro-rotation application, as FBP is for CT application.

The radiologist’s conundrum: benefits and costs of increasing CT capacity and utilization–a commentary

This paper is a timely reminder that, whatever the differences in health-care systems, the problems faced by Radiology across the world are often very similar. The rise in the clinical use of computed tomography (CT) is incontrovertible: the flexibility of modern CT systems offers little resistance to the demand for intensive examinations and high productivity, and there has been an extraordinary expansion in the number of clinical applications to which the technique can now be applied. Many of these have been major advances in investigative medicine, fully justified by the contribution they make to patient care. In other areas, however, there is doubt, and, as the authors point out, the expansion of the technique may at times be driven not by justifiable clinical need, but by pressure to perform financially or by demand from referrers. Today no institution can afford to ignore the tension between resource and demand that results from the technical capacity and application of CT, and there is general perception that a need exists for some constraint in utilisation. In Europe asking for examination by CT is regarded as a request for a clinical opinion by the radiologist, rather than a test that is “ordered” by a clinician. In Europe the use of CT, in common with other radiation-based tests, is governed by radiation protection law, which requires that the examination should be justified by a clinical indication and that the technique should be optimised to deliver a result in the lowest radiation exposure appropriate– ALARA (as low as reasonably achievable). It might be expected, therefore, that in Europe “the CT problem” should not exist. However, there is significant concern–and also evidence-that clinical use of CT is not as tightly constrained as it might be and that the rising use of the technique has been accompanied by increased variation in examination technique and therefore exposure. Despite the introduction of Ionizing Radiation Regulations, it appears that we have not always achieved the spirit of the European Union Directive that led to them. Successive surveys have shown that variability in practice appears to be increasing rather than coming under control. This may partly be due to the pressure of increasing demand on radiology generally. Faced with rising workload, radiologists may come to rely on “catch all” examination protocols rather than carefully targeting the investigation to the current clinical need. This may explain why the “chest, abdomen and pelvis” request seems to have become so common. Undoubtedly another reason for variable practice is that the evidence base is not as strong as it might be. Although the clinical applications of CTwerewell documented in the past, a striking feature of the recent literature is that studies of clinical application have largely been limited to new applications facilitated by technical advances, and the practice of established indications has not been updated. Most importantly, we lack firm criteria on what constitutes a threshold exposure in individual clinical applications, an approach that would lead to dose reference levels and end the clinical use versus protection debate to which the authors refer. This has led to reliance on clinical guidelines such as those on clinical indications that have been published in the UK by the Royal College of Radiologists and those from a European working group giving general recommendations on exposure and dose. More studies are needed to give this work a robust evidence base, and there is also a need to educate clinical referrers; in this respect the scoring system reported by the authors represents an interesting contribution to the debate. If we are responsible in our practice, CT will only be performed on the basis of sound clinical justification, using the minimal acceptable exposure, when the potential benefit is judged to outweigh the risk, and supported by a clinical evidence base that is continually updated by sound studies of clinical practice and exposure constraint. It seems inescapable logic that in this clinical setting the radiologist has the appropriate professional training to be the gate keeper and guardian of the patients’ interests in the face of financial and clinical pressures to act otherwise. S. Golding University of Oxford,Oxford, UK

Computer‐Aided Diagnosis in Thoracic Computed Tomography

SummaryCurrent computed tomography (CT) technology allows for isotropic, sub‐millimetre resolution acquisition of the thorax in a few seconds. These thin‐slice chest scans have become indispensable in thoracic radiology, but have also increased the time and effort required from radiologists for reporting. Industry has focused on the development of computer‐aided diagnosis (CAD) tools to facilitate the interpretation of thoracic CT data. In this paper I discuss the three most ‘senior’ CAD applications for chest CT: nodule detection, nodule volumetry and quantification of emphysema. Are these applications ready for widespread application?

X‐ray micro‐CT applied to natural building materials and art objects

AbstractIn recent years, x‐ray micro‐CT has become an important tool for investigating all kinds of materials. The technique uses x‐ray transmission images of a sample to create a 3D representation of the specimen. Owing to its nondestructive nature, it is especially suited to investigate rare or expensive samples. This article aims to point out the potential x‐ray computed tomography (CT) has to offer to the preservation of cultural heritage and the world of art. Research was performed at the UGCT facility of the Ghent University (Belgium), using a ‘state of the art’ x‐ray microtomograph. In this article, the results for two applications of x‐ray CT are shown and discussed. The first application is the localization of salts in sandstone and limestone, as a contribution to the European Saltcontrol project. As for the second application, several bronze artifacts were scanned and reconstructed. This allows one to look at the interior composition of the sample and detect possible signs of reparation. Copyright © 2008 John Wiley &amp; Sons, Ltd.