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Commentary |
Günter Dombrowe, the President of the British Institute of Radiology (BIR), introduced the theme of this year's Conference, and explained its dual purpose – to highlight the contributions of medical and information technologies towards improving clinical practice, patient outcome and health economics; and to pay tribute to the pioneering work of Sir Godfrey Hounsfield, the inventor of CT scanning, perhaps the key technology of the digital imaging age.
This Commentary provides an overview of some of the important topics discussed at the Conference. Some of the key presentations are also included in this issue.
Elizabeth Beckmann reminded the audience of the early days of CT – the excitement generated by the images of the brain shown at the 32nd Congress of the BIR on 20 April 1972, the delightfully understated title of Sir Godfrey's lecture – "Computerised axial tomography, a new means of demonstrating some of the soft tissue structures of the brain without the use of contrast media", and the subsequent publications in the BJR [1, 2]. The enduring memory of this and other early developments is that so much was achieved with so little money. Was Sir Godfrey one of the last brilliant, intuitive, string and sealing wax physics brigade?
The first of the two nominated Hounsfield lecturers, Willi Kalender gave a comprehensive review of the past, present and future of CT from a physics and technology standpoint. He pointed out that there had been three distinct phases of development: (1) the 1970s had been a time of rapid development with second, third and fourth generation scanners; (2) the 1980s had been a period of stagnation with the competing development of MRI (the late 1980s was the only time during a 30 year period when there was no increase in the number of CT scanners in Germany); (3) the 1990s were the renaissance years, particularly with the introduction of spiral CT and multidetector arrays.
Scan times are now typically 0.3 s to 0.5 s per full 360° scan and 10–30 s for the whole body. The first figure is important for temporal resolution, especially in cardiac applications, and one of the limitations on faster times is the centrifugal force to which sensitive components such as the X-ray tube are subjected [3]. To achieve better temporal resolution increased electronic control of the beam and possibly multiple tube designs are being explored.
Improvements in total scan time will be achieved through further development of wider detector arrays, possibly towards flat panel detectors. This will in turn require X-ray tubes with an even higher peak output, as the total flux of photons required to image a given volume remains roughly the same.
Like for like, patient doses have been reduced with tube current modulation both on rotation from anteroposterior (AP) to lateral projections and as the beam traverses the body from high to low attenuating regions. Achieving the same counting statistics on all data is a worthwhile goal [4, 5].
Since 1990 the emphasis has been on scanning volumes rather than slices and one of the landmarks has been to achieve isotropically uniform spatial resolution, typically in the range 0.4–0.6 mm [6]. It is important to recall that for isotropic resolution, radiation dose to the patient increases with the fourth power of the resolution element.
These improvements must also be seen in the context of global use of radiology. CT is a relatively high dose technique, now accounting for 25% of all radiation exposure, and there must be strong clinical justification for its use, and in particular serial, repeat whole body scans.
The future for CT is hidden from view but there are many possibilities and it is worthwhile to summarize Kalender's predictions – more detector rows; shorter effective scan times; higher resolutions and more tissue parameters (there is renewed interest in superimposing, e.g. a calcium density map on a real density map obtained by dual energy CT [7]); lower doses (of course!).
The second nominated Hounsfield lecturer, Adrian Dixon, reviewed the clinical advances in CT. Two important issues in particular were addressed:
As a specific example of the clinical issues, he considered the impact of multidetector CT on abdominal problems. The improved anatomical resolution of modern helical CT scanners enables the diagnosis of acute appendicitis or the cause of small bowel obstruction to be made with a high degree of accuracy [8]. Consequent on its multitasking abilities, CT is increasingly being used as a means of triaging patients and facilitating early discharge for those without serious disease – with obvious benefits to the patients and cost savings to the NHS [9].
CT has become so good that in many areas of radiology the real questions are now (a) is there a role for plain film radiography? (b) when should ultrasound be used? (c) is there a role for MR other than to avoid the use of ionizing radiation?
This success has come at a price: clinicians are tending to request a CT scan without fully examining the patient; surgeons are reluctant to operate without high quality imaging; for outpatients in oncology the number of requests for CT staging is starting to approximate the number of visits to hospital. However, Dixon was able to conclude on a positive note. For the patient CT has replaced some very unpleasant investigations.
The tribute to Hounsfield concluded with a more specialized lecture from Albert de Roos on cardiac CT. Roos summarized the technical considerations for multislice CT in cardiac scanning – low contrast detection, spatial resolution at high contrast, temporal resolution, scan time and patient dose. The choice of acquisition variables and reconstruction characteristics is very dependent on the clinical problem under investigation.
De Roos then reviewed a wide range of applications including: the quantitative assessment of coronary artery calcification [10, 11]; the assessment of coronary artery morphology; stent and graft patency; the selection of patients for invasive therapy; assessment of the anatomy of pulmonary veins and the investigation of acute chest pain. In the last of these applications there is now a one-stage protocol, i.e. the nirvana of the "one stop shop" to diagnose accurately both cardiac and non-cardiac causes of chest pain [12].
The Mackenzie Davidson lecture, delivered by Nicola Strickland, touched on many aspects of modern imaging but concentrated on information technology, especially PACS.
PACS has now become a mature technology, especially as a result of the DICOM standard and network protocols. It clearly has the potential to improve workflow and productivity but does not, in itself, solve departmental inefficiencies and may highlight them. It is not a "quick fix" and must be an integral part of workflow engineering.
Looking to the future, speech recognition and web browsers will be developed further. The electronic patient record remains a major challenge, since the facilities provided need to match the service being provided. A good example is home reporting – a full work load requires a full diagnostic service, emergency reporting needs only more limited facilities.
Strickland concluded that technology provides the means for improving workflow and productivity – the challenge is to optimize the use of technology to maximize productivity in a clinically efficient way.
Manufacturers' views of the use and development of technology were also presented. Hermanns Requardt from Siemens Medical Solutions reminded us that, worldwide, challenges to healthcare systems are dominated by two main topics – demographic factors and progress in medicine. In diagnostic radiology, as in some other branches of medicine, for example molecular/genetic medicine, the challenge now is not a lack of information but a flood of information. Drawing an analogy from industry where knowledge management systems are commonplace, Requardt predicted that information technology would bring about a paradigm shift in medicine if it could facilitate the formation of a clinical knowledge database and enable this to be used to complement the data from the individual patient.
Jacques Souquet from Philips Medical Systems considered some other aspects of the impact of future technology on medical imaging. Picking up a theme from the previous speaker on progress in medicine, he pointed out that knowledge doubling times have fallen from about 8 years in 1970 to 1 year in 2001. Increased use of computer-aided decisions is one way to improve management of data, for example nodule identification in a radiograph, using embedded medical knowledge to reduce avoidable medical errors, genetic algorithms to discover diagnostic patterns in huge data sets.
Souquet reminded us that much remains to be done. There are still several diseases for which no diagnostic test is available and the development of drugs to correct specific genetic flaws that are biological causes of cancer has a long way to go. In conclusion, he threw out two challenges:
Jane Guinn from Kodak Ltd concluded the session by comparing the techniques of computed radiography (CR) and digital radiography (DR) from the standpoint of workflow patterns. She listed 16 distinct stages in the production of a traditional analogue film, many involving radiographer movement. CR removed only two steps, DR removed nine. This had a big impact on average examination time and in a busy general radiography room, on patient waiting time. Unfortunately DR does not provide the flexibility of CR for several examinations.
Peter Williams delivered the Silvanus Thomson Memorial Lecture. With the somewhat enigmatic title "Things can only get better" he reviewed the development of external beam radiotherapy treatment delivery, concentrating on current developments and future promises.
Early examples of "things getting better" included megavoltage therapy with Co-60; isocentric mounting; electrons as well as X-rays; anatomical data from the CT scanner for treatment planning. For a few years the ability to model tumours exceeded the ability to treat, which was restricted to a cylinder.
In 1987 the multileaf collimator (MLC) became available for beam shaping and as with most really worthwhile medical developments, there were no formal health quality assessments or clinical trials.
MLCs led to intensity-modulated radiotherapy (IMRT), essentially conformal therapy for difficult targets [13, 14], and at the same time electronic portal imaging was being developed to provide active control of beam direction rather than a passive verification system.
Williams then discussed the current development of real time tumour tracking to counteract patient movement by mounting a diagnostic machine with fluoroscopic, radiographic and CT capabilities onto the treatment linear accelerator. Examples of improved set-up were shown for lung and bladder treatments – image-guided radiotherapy will certainly make things better!
For the future, although physicists and engineers are not yet spent (vide the next topic of proton therapy), they will need help from other disciplines, e.g. molecular biologists and geneticists (biological targeting for anoxia and metabolism, and selective targeting of tumour cells), and from radiobiologists (for example to exploit the information on bystander effects coming from microbeam studies).
As a fitting sequel to the Silvanus Thomson Memorial Lecture, Bleddyn Jones presented the case for particle therapy, especially with protons. The theoretical advantages of using the Bragg dose peak to improve the therapeutic ratio have been known for many years. Unfortunately, for a 60 MeV beam the peak is at only 3 cm depth and treatment is limited to quite superficial tumours. Notwithstanding, over 1200 choroidal melanomas have been treated successfully at the Clatterbridge Hospital.
Work by Lomax et al [15] has shown that for treatment of the breast and regional nodes, a 9-field photon IMRT approach can either produce similar dose homogeneity across the planning treatment volumes to that of a proton plan, or similar sparing of dose to both lungs and the heart, but not both.
Jones estimated that 10–20% of patients might be better treated by particle radiotherapy and believes that technical improvements in physics, bioengineering and computing, especially in robotics and particle delivery, now make treatment with a 200 MeV beam, with Bragg peak depths approaching 20 cm, a practical proposition. It is anticipated that this will lead to a big increase in demand for particle therapy in the UK [16].
The Conference concluded with two further papers in diagnostic imaging. Catherine Owens gave a wide-ranging review of the changing practice of paediatric imaging. The diagnostic capability and accuracy of multidetector CT (MDCT) angiography was compared with echocardiography, cardiac catheterization and surgery in the assessment of the great vessels in 40 consecutive patients (mean age 5 years) with congenital heart disease. MDCT was accurate, showing good agreement with interventional catheter and surgery and provided additional information. Effective doses of radiation were low – ranging from 0.97 mSv in neonates to 1.7 mSv in adolescents [17].
Magnetic resonance coronary angiography and late-enhancement imaging have been shown to be feasible in children who had undergone arterial switch for transposition of the great arteries. Diagnostic quality images were acquired in 72% of the coronary arteries imaged and this rose to 100% in subjects over 10 years old [18].
Finally, Peter Ell discussed the contribution of PET/CT to improved patient management. Whilst acknowledging the important contribution in neurology and cardiology, in the limited time available and in the context of the Conference, Ell concentrated on oncology. Four distinct areas were covered, diagnosis, staging, radiotherapy planning and treatment monitoring.
Two very different challenges for this wonderful technique were highlighted. At the cutting edge of research there are almost unlimited opportunities for PET/CT to be used to assess the biology of individual response to treatment [19]. Whilst recognizing the importance of F-18 fluorodeoxyglucose in oncology, Ell emphasised the need to look at a wide range of other novel markers that are being developed, aimed at imaging proliferation [20, 21], hypoxia, angiogenesis, apoptosis, etc.
At the other extreme there is the huge problem of diffusion of technology in a cost-effective way so that, on a day-to-day basis, many more of the millions of cancer sufferers can benefit from the power of multimodality imaging.
Ell's concluding remarks were:
These remarks were, of course, addressed to PET/CT but, in many respects, with suitable changes of wording, could be applied to the impact of other technological advances discussed during the 2005 President's Conference. We commend to you the full articles contributed by the speakers in this issue of the Journal.
Acknowledgments
I am grateful to Fergus Gleeson and Günter Dombrowe for helpful contributions to this Commentary.
References
This article has been cited by other articles:
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  BJR review of the year - 2006 Br. J. Radiol., March 1, 2007; 80(951): 147 - 151. [Full Text] [PDF]
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