G Morgan-Hughes

Highly accurate coronary angiography with submillimetre, 16 slice computed tomography

Objective: To assess submillimetre coronary computed tomographic angiography (CTA) in comparison with invasive quantitative coronary angiography as the gold standard and to examine the effect of significant coronary artery calcification (CAC), which is known to impede lumen visualisation, on the accuracy of the examination. Methods: After invasive coronary angiography, 58 patients underwent coronary imaging with a GE Lightspeed 16 computed tomography (CT) system. CAC was quantified after an ECG triggered acquisition with a low tube current. Coronary CTA was performed with retrospective ECG gating and a 16 × 0.63 mm collimation and was reconstructed with an effective 65–250 ms temporal resolution. All 13 major coronary artery segments were evaluated for the presence of ⩾ 50% stenosis, and compared with the gold standard. Results: One patient moved and could not be evaluated. All segments (except occluded segments) were evaluated for 57 patients. Overall the accuracy of coronary CTA for detection of ⩾ 50% stenosis was: sensitivity 83%, specificity 97%, positive predictive value 80%, and negative predictive value 97%. The number of diseased coronary arteries was correctly diagnosed in 34 of 38 (89%) patients overall. Altogether 21 of 57 (37%) patients had a CAC score ⩾ 400, which was predefined as representing significant CAC. Excluding these patients from the analysis improved the accuracy of coronary CTA to a sensitivity of 89%, specificity 98%, positive predictive value 79%, and negative predictive value 99%. Conclusions: Non-invasive coronary angiography with submillimetre CT is reliable and accurate. It appears that a subgroup of patients may be selected based on CAC score in whom the investigation has even higher accuracy. Coronary CTA has reached the stage where it should be considered for a clinical role. Further research is required to define this role.

A comparison of radiation doses between state-of-the-art multislice CT coronary angiography with iterative reconstruction, multislice CT coronary angiography with standard filtered back-projection and invasive diagnostic coronary angiography

Objective To accurately compare the radiation dose between prospectively gated cardiac multidetector CT (with and without iterative reconstruction) and diagnostic invasive coronary angiography using the latest International Commission on Radiological Protection 103 (ICRP) tissue weightings. Design, setting and patients A retrospective analysis of consecutive patients presenting to a university teaching hospital for investigation of coronary artery disease. Radiation doses for each technique were calculated using computational Monte Carlo modelling of a standard Cristy phantom rather than the application of previously published conversion factors. While these have frequently been used in other studies, they are based on out-dated ICRP tissue weightings (ICRP 60) and are for the whole chest rather than for structures irradiated in cardiac imaging. In order to allow a comparison, doses were calculated and expressed in terms of effective dose in millisieverts (mSv). Results From a population presenting for angiography within a clinical service, the median radiation dose from cardiac CT with standard filtered back-projection (84 patients, 5.4 mSv) was comparable with the dose from invasive diagnostic coronary angiography (94 patients, 6.3 mSv). The dose for cardiac CT using iterative reconstruction was significantly lower (39 patients, 2.5 mSv). Conclusion The median effective dose from cardiac CT with standard filtered back-projection was comparable with the effective dose from invasive coronary angiography, even with application of the most contemporary ICRP tissue weightings and use of cardiac specific volumes. Cardiac CT scanning incorporating iterative reconstruction resulted in a significant reduction in the effective dose.

Three dimensional volume quantification of aortic valve calcification using multislice computed tomography

Objective: To assess a new multislice computed tomography (CT) technique for three dimensional quantification of aortic valve calcification volume (3D AVCV) and to study the relation between stenosis and calcification of the aortic valve. Methods: 50 patients with echocardiographic calcification of the aortic valve underwent two separate ECG triggered multislice CT for quantification of 3D AVCV. The agreement between the two 3D AVCV scores was assessed and 3D AVCV was compared with echocardiographic markers of severity of aortic stenosis. Results: Overall the level of agreement between the two 3D AVCV scores was excellent (median interscan variability 7.9% (interquartile range 10.1); correlation coefficient, r = 0.99; repeatability coefficient 237.8 mm3 (limits of agreement −393 to 559 mm3)). However, the magnitude of the 3D AVCV did influence the interscan variability. The 3D AVCV correlated closely with the maximal predicted transvalvar gradient (r2 = 0.77) and aortic valve area (r2 = 0.73). Conclusions: Multislice CT provides a technique for quantifying 3D AVCV that has good reproducibility. There is a close non-linear relation between echocardiographic parameters of severity of valve stenosis and 3D AVCV scores.

Multidetector row computed tomography: imaging congenital coronary artery anomalies in adults

The quality of the imaging of the main coronary arteries and side branches provided by multidetector row computed tomography (MDCT) may have importance when assessing congenital coronary artery anomalies. This review discusses the rationale for using MDCT for this indication and examines the advantages and disadvantages of the technique. Examples of MDCT imaging of congenital coronary artery anomalies are presented. These images provide persuasive evidence to support clinical use of MDCT cardiac imaging in the context of suspected congenital coronary artery anomalies as a first line investigation.

Cardiac CT: are we underestimating the dose? A radiation dose study utilizing the 2007 ICRP tissue weighting factors and a cardiac specific scan volume

AIM To calculate the effective dose from cardiac multidetector computed tomography (MDCT) using a computer-based model utilizing the latest International Commission on Radiation Protection (ICRP) 103 tissue-weighting factors (2007), to compare this dose with those calculated with previously published chest conversion factors and to produce a conversion factor specific for cardiac MDCT. MATERIALS AND METHODS An observational study of 152 patients attending for cardiac MDCT as part of their usual clinical care in a university teaching hospital. The dose for each examination was calculated using the computer-based anthropomorphic ImPACT model (the imaging performance assessment of CT scanners) and this was compared with the dose derived from the dose-length product (DLP) and a chest conversion factor. RESULTS The median effective dose calculated using the ImPACT calculator (4.5 mSv) was significantly higher than the doses calculated with the chest conversion factors (2.2-3 mSv). CONCLUSION The use of chest conversion factors significantly underestimates the effective dose when compared to the dose calculated using the ImPACT calculator. A conversion factor of 0.028 would give a better estimation of the effective dose from prospectively gated cardiac MDCT.

Radiation-reduction strategies in cardiac computed tomographic angiography

Ionizing radiation has long been known to increase the risk of cancer. X-rays and γ-rays are officially classified as a carcinogen by the World Health Organizations International Agency for Research on Cancer.(1) Of the 5 billion imaging investigations performed worldwide two-thirds employ ionizing radiation.(2) Diagnostic x-rays are the largest man-made source of radiation exposure to the general population, and computed tomography (CT) represents the largest proportion of these.(3) Diagnostic CT has seen a dramatic increase in applications in the last two decades, not least in the higher dose applications. Whilst the increased use of CT has undoubtedly been of patient benefit, it inevitably will be associated with an increase in malignancy due to medical exposure. In fact a recent study from the USA has estimated that the CT examinations performed in 2007 could result in 29,000 future cancers based on current risk estimations.(4) Whilst the numbers in the UK will be less (only 4 million examinations are performed compared to 70 million), it is clear that it is the responsibility of all radiologists to carefully examine their CT techniques and protocols with the aim to reduce the dose of examinations without compromising their accuracy. Cardiac computed tomographic angiography (CTA) initially was a very high dose application. However, both clinicians and CT system manufacturers have done a large amount of work to reduce dose. Dramatic changes have been achieved and the aim of this review is to highlight these. However, such developments are not exclusively applicable to cardiac CTA and many can be utilized in CT in general.

Imaging the pericardium: appearances on ECG-gated 64-detector row cardiac computed tomography

Multidetector row computed tomography (MDCT) with its high spatial and temporal resolution has now become an established and complementary method for cardiac imaging. It can now be used reliably to exclude significant coronary artery disease and delineate complex coronary artery anomalies, and has become a valuable problem-solving tool. Our experience with MDCT imaging suggests that it is clinically useful for imaging the pericardium. It is important to be aware of the normal anatomy of the pericardium and not mistake normal variations for pathology. The pericardial recesses are visible in up to 44% of non-electrocardiogram (ECG)-gated MDCT images. Abnormalities of the pericardium can now be identified with increasing certainty on 64-detector row CT; they may be the key to diagnosis and therefore must not be overlooked. This educational review of the pericardium will cover different imaging techniques, with a significant emphasis on MDCT. We have a large research and clinical experience of ECG-gated cardiac CT and will demonstrate examples of pericardial recesses, their variations and a wide variety of pericardial abnormalities and systemic conditions affecting the pericardium. We give a brief relevant background of the conditions and reinforce the key imaging features. We aim to provide a pictorial demonstration of the wide variety of abnormalities of the pericardium and the pitfalls in the diagnosis of pericardial disease.

Usefulness of 64-Detector Row Computed Tomography for Evaluation of Intracoronary Stents in Symptomatic Patients With Suspected In-Stent Restenosis

To determine whether 64-slice multidetector computed tomographic coronary angiography (MDCTA) can accurately assess the coronary artery lumen in symptomatic patients with previous coronary artery stents and potential in-stent restenosis (ISR). The primary aim was to determine the accuracy of binary ISR exclusion using MDCTA compared with invasive catheter angiography (ICA). Secondary aims were comparisons of stent dimensions measured using MDCTA and variables that affect accuracy. Forty patients with previous stent placement underwent both ICA and 64-slice MDCTA after elective presentation with chest pain, and ICA quantitative coronary angiographic data were used as the reference standard. Thirty-six men and 4 women (age 64 +/- 10 years; range 44 to 83) with 103 stents (2.8 +/- 1.6 stents/patient) were comparatively evaluated (stent exclusion rate 9.6%). There were 45 bare-metal and 58 drug-eluting stents (20 +/- 18 months after implantation) with an average diameter of 3.23 +/- 0.7 mm. Overall accuracy for the detection of significant ISR showed sensitivity, specificity, and positive and negative predictive values of 85%, 86%, 61%, and 96% for proximal stents > or =3 mm, which improved to 100%, 94%, 81%, and 100%; if the visible luminal diameter on MDCTA was <1.5 mm, accuracy decreased to 40%, 84%, 29%, and 90%, respectively. In conclusion, 64-slice MDCTA assessment of symptomatic patients with suspected clinically significant ISR is a realistic alternative to ICA if reference stent diameter is > or =2.5 mm and visible lumen cross-sectional diameter is > or =1.5 mm, for which a negative MDCTA result virtually excludes the presence of significant ISR.

Imaging the heart valves using ECG-gated 64-detector row cardiac CT.

Multi-detector row cardiac CT imaging demonstrates clinical usefulness in valvular heart disease, for which CT has not been traditionally used. Electrocardiographic (ECG)-gated CT coronary angiography also has an established clinical role with an increasingly solid evidence base, and the same data set in these patients also provides valuable information about chamber and valvular structure and function; this information should also be considered when interpreting cardiac CT and non-ECG gated thoracic imaging. Although true flow data cannot be achieved using CT, as with echocardiography and MRI, there are a number of imaging features that may be used when interpreting and inferring valve pathology. This article discusses the role of currently available imaging modalities and the rationale for cardiac CT, while focusing on the CT interpretation of valvular heart disease with respect to the relevant pathophysiology and management options that have importance to the radiologist. A suggested method of post-processing image review is provided with reference to a variety of normal and pathological pictorial illustrations.

Refined computed tomography of the thoracic aorta: the impact of electrocardiographic assistance.

There have been a number of advances in helical computed tomography (CT) in recent years, which have had a beneficial impact on the quality of imaging of the thoracic aorta. These advances include sub-second gantry rotation, multislice acquisition, and the use of electrocardiographic (ECG) assistance. We examine these techniques with emphasis on the principles behind ECG assistance and its use to reduce aortic motion artefact. We highlight examples of ECG-assisted multislice CT in a spectrum of pathologies of the thoracic aorta.