Detection of simulated pulmonary nodules by spiral CT
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272 CLINICAL RADIOLOGY 2 Bahist B, Frager DH, Suster B. Abdominal CT findings when the References superior vena cava, brachiocephalic vein or subclavian vein is obstructed. Am J Roentgen01 1996;161:1457-1463. 3 Yentis SM, Hirsch NP, Smith GB. Anaesthesia A to Z, 1st ed. London: Butterworth-Heinemann Ltd, 1993;91-92. 1 Coakley FV, Cohen MD, Johnson MS, Gonin R, Hanna MP. Effect of Breathing on the Detection of in vivo Simulated Pulmonary Nodules by Spiral CT. Clin Radio1 1998;53:506-509. SIR - We thank Drs Price, Duel1 and Wyatt for their comments regarding our paper ‘Azygos Reflux: a CT Sign of Cardiac Tamponade’. We agree with their comments that there are many causes of raised central venous pressure and that haemodynamics dictate that when the pressure in the SVC is greater than the azygos vein, that reflux will occur. We would emphasize that we do not state our findings to be specific for cardiac tamponade. However, in the correct clinical setting with the presence of a pericardial effusion, the diagnosis should be considered because the immediate management is critical to patient care. In all three of our cases, the diagnosis was only considered after the CT was performed. S. R. HARRIES B. M. FOX C. A. ROOBOTTOM Derriford Hospital Plymouth, UK DETECTION OF SIMULATED PULMONARY NODULES BY SPIRAL CT SIR - We thank Professor Robinson for his interest in our paper [ 11. Clearly specificity is of critical importance in the diagnosis of pulmonary metastases, and in a previous pathological study we reported the common causes of false-positive results [2]. False-positive results in the current study did not have a pathological reference standard, and therefore it was not possible to determine if false-positive nodules on adjacent slices, or in corresponding positions on different CT techniques (i.e. breath-hold versus breathing) represented the same or different lesions. The interdependence of these observations was therefore unknown, and for this reason no meaningful statistical analysis of false positives, and hence specificity, can be performed. The two biostatisticians who co-authored our study (R.G. and M.P.H.) were adamant that comparison of such data was unsound. For the record, a single false-positive result was recorded by the readers on the breath-hold images, compared with a total of 10 on the breathing images. The respective number of true-positive results was 103 and 102. Readers may draw their own conclusion as to whether the difference in the number of false-positive results is clinically significant. SIR - Dr Coakley and colleagues [l] describe an elegant experimental study indicating the sensitivity of spiral CT in detecting pulmonary nodules during quiet breathing and breath holding. In clinical practice, specificity is also of critical importance, so it would be helpful to know how many false-positive calls their observers made. I have some difficulty with their statement that the number of false positives cannot be analysed - the authors must already have classified each observation of a nodule as either a true-positive or a false-positive call. Whilst the difficulty in correlating individual false-positive calls between observers and between techniques is apparent, surely there can be no doubt about the actual number of false positives recorded by each observer with each technique. FERGUS COAKLEY Department of Radiology, University of California, San Francisco, CA, USA References 1 Waters DJ, Coakley FV, Cohen MD, et al. Detection of pulmonary metastases with helical CT: A clinicopathologic study in dogs. J Comput Assist Tomog 1998;22:235-240. PHILIP ROBINSON Division of Clinical Radiology St James’ University Hospital Leeds, UK 2 Coakley FV, Cohen MD, Johnson MS, Gonin R, Hanna MP. Effect of breathing on the detection of in vivo stimulated pulmonary nodules by spiral CT. Clin Radial 1998;53:506-509.
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Transcript of Detection of simulated pulmonary nodules by spiral CT
272 CLINICAL RADIOLOGY
2 Bahist B, Frager DH, Suster B. Abdominal CT findings when the References superior vena cava, brachiocephalic vein or subclavian vein is obstructed. Am J Roentgen01 1996;161:1457-1463.
3 Yentis SM, Hirsch NP, Smith GB. Anaesthesia A to Z, 1st ed. London: Butterworth-Heinemann Ltd, 1993;91-92.
1 Coakley FV, Cohen MD, Johnson MS, Gonin R, Hanna MP. Effect of Breathing on the Detection of in vivo Simulated Pulmonary Nodules by Spiral CT. Clin Radio1 1998;53:506-509.
SIR - We thank Drs Price, Duel1 and Wyatt for their comments regarding our paper ‘Azygos Reflux: a CT Sign of Cardiac Tamponade’. We agree with their comments that there are many causes of raised central venous pressure and that haemodynamics dictate that when the pressure in the SVC is greater than the azygos vein, that reflux will occur.
We would emphasize that we do not state our findings to be specific for cardiac tamponade. However, in the correct clinical setting with the presence of a pericardial effusion, the diagnosis should be considered because the immediate management is critical to patient care. In all three of our cases, the diagnosis was only considered after the CT was performed.
S. R. HARRIES B. M. FOX C. A. ROOBOTTOM Derriford Hospital
Plymouth, UK
DETECTION OF SIMULATED PULMONARY NODULES BY SPIRAL CT
SIR - We thank Professor Robinson for his interest in our paper [ 11. Clearly specificity is of critical importance in the diagnosis of pulmonary metastases, and in a previous pathological study we reported the common causes of false-positive results [2]. False-positive results in the current study did not have a pathological reference standard, and therefore it was not possible to determine if false-positive nodules on adjacent slices, or in corresponding positions on different CT techniques (i.e. breath-hold versus breathing) represented the same or different lesions. The interdependence of these observations was therefore unknown, and for this reason no meaningful statistical analysis of false positives, and hence specificity, can be performed. The two biostatisticians who co-authored our study (R.G. and M.P.H.) were adamant that comparison of such data was unsound. For the record, a single false-positive result was recorded by the readers on the breath-hold images, compared with a total of 10 on the breathing images. The respective number of true-positive results was 103 and 102. Readers may draw their own conclusion as to whether the difference in the number of false-positive results is clinically significant.
SIR - Dr Coakley and colleagues [l] describe an elegant experimental study indicating the sensitivity of spiral CT in detecting pulmonary nodules during quiet breathing and breath holding. In clinical practice, specificity is also of critical importance, so it would be helpful to know how many false-positive calls their observers made. I have some difficulty with their statement that the number of false positives cannot be analysed - the authors must already have classified each observation of a nodule as either a true-positive or a false-positive call. Whilst the difficulty in correlating individual false-positive calls between observers and between techniques is apparent, surely there can be no doubt about the actual number of false positives recorded by each observer with each technique.
FERGUS COAKLEY Department of Radiology, University of California,
San Francisco, CA, USA
References
1 Waters DJ, Coakley FV, Cohen MD, et al. Detection of pulmonary metastases with helical CT: A clinicopathologic study in dogs. J Comput Assist Tomog 1998;22:235-240.
PHILIP ROBINSON Division of Clinical Radiology St James’ University Hospital
Leeds, UK
2 Coakley FV, Cohen MD, Johnson MS, Gonin R, Hanna MP. Effect of breathing on the detection of in vivo stimulated pulmonary nodules by spiral CT. Clin Radial 1998;53:506-509.
