220
CLINICAL RADIOLOGY
60 °. Colour Doppler hnaging (CDI) is an easy and accurate means of obtaining waveforms at appropriate Doppler angles. The visualization of vessels with the use of CDI should be the preferred method in the Doppler waveform analysis of small arteries, e.g. arcuate and interlobar arteries. S. S. OZBEK
Department of Diagnostic Radiology Ankara University Ibn-i Sina Hospital Samanpazari 06100 Ankara Turkey
References
1 Kim SH, Kim WH, Choi BI, Kim CW, Duplex Doppler US in patients with medical renal disease: Resistive index vs serum creatinine level. Clinical Radiology 1992;45:85-87. 2 Nelson TR, Pretorius DH. The Doppler signal: Where does it come from and what does it mean? American Journal of Roentgenology 1988; 151:439-447.
ULTRASONIC ATTENUATION O F FIBROADENOMA O F THE BREAST SIR - I read with interest the paper by Guyer et aL [1]. I would like to make two comments. First, whenever a new sign is described [2], it is essential to calculate not only its sensitivity, but also its specificity and, preferably, its positive predictive value. The two latter factors could not have been estimated in Guyer et al.'s study unless malignant lesions were included. Without demonstrating that a sign is absent or rare in malignant lesions, it cannot be affirmed that the sign suggests that a lesion is benign. The second comment is that the authors had the prior knowledge that all lesions included in the study were benign and that could have opened the door for observer's bias. I have reviewed the breast ultrasound findings of 13 lesions which had histopathological proof. T h e ultrasound images were displayed in a random order with the patient's identification masked to avoid observer's bias. The sign described by Guyer et al. was positive in four out of the ten benign lesions a sensitivity of 40%, the same as the one found by Guyer et al. However, at least one, and possibly two, of the three malignant lesions (33% 66%) also showed the sign. Admittedly the numbers are small, but my findings suggest it is possible that this sign may well have a low specificity. A. M. A. H U S I E N
SIR I thank Dr Ozbek for the comments on my article. I agree that colour Doppler imaging is superior to conventional duplex Doppler ultrasound in identifying small arteries in the kidney and I think that colour Doppler imaging will be helpful in saving time for the acquisition of Doppler spectrum. I also agree with him that the signal-to-noise ratio is low at Doppler angles greater than 60°; however, I do not agree that Doppler indices, including resistive index which I used in my article, are not angleindependent when the Doppler angle is greater than 60 °. At Doppler angles greater than 60 °, the higher range of error in Doppler spectral analysis is not because of angle-dependence of the indices but is due to lower signal-to-noise ratio. Using conventional duplex Doppler ultrasound, in my experience, it is not difficult to obtain Doppler waveforms with adequate signal-tonoise ratio in the areas of the arcuate or the interlobar arteries of the kidney with audiovisual assistance. - -
S. H. K I M
Department of Diagnostic Radiology Seoul National University Hospital 28 Yongon-dong Chongnu-gu Seoul 110-744 Republic of South Korea
References
Breast Screening Unit Kettering General Hospital Kettering Northants NN16 8UZ
1 Guyer PB, Dewbury KC, Rubin CM, Butcher C, Royle GT, Theaker J. Ultrasonic attenuation in fibroadenoma of the breast. Clinical Radiology 1992;45:175-178. 2 Gardner M J, Altman DG. Statistics with confidence. British Medical Journal, London 1989:97-99. SIR Thank you for letting me see Dr Husien's letter in response to the publication o f our paper on fibroadenomas. All we set out to do was to alert colleagues to the echo-bright zone between the fibroadenoma and the accompanying attenuating shadow, and all that we claimed was that this 'might' be a sign to point towards a benign diagnosis. We feel that the numbers are too small to attempt any reasonable statistical analysis. - -
P. B. G U Y E R
Department of Radiology Royal South Hants Hospital Graham Road Southampton S09 4PE
CLINICAL RADIOLOGY
60 °. Colour Doppler hnaging (CDI) is an easy and accurate means of obtaining waveforms at appropriate Doppler angles. The visualization of vessels with the use of CDI should be the preferred method in the Doppler waveform analysis of small arteries, e.g. arcuate and interlobar arteries. S. S. OZBEK
Department of Diagnostic Radiology Ankara University Ibn-i Sina Hospital Samanpazari 06100 Ankara Turkey
References
1 Kim SH, Kim WH, Choi BI, Kim CW, Duplex Doppler US in patients with medical renal disease: Resistive index vs serum creatinine level. Clinical Radiology 1992;45:85-87. 2 Nelson TR, Pretorius DH. The Doppler signal: Where does it come from and what does it mean? American Journal of Roentgenology 1988; 151:439-447.
ULTRASONIC ATTENUATION O F FIBROADENOMA O F THE BREAST SIR - I read with interest the paper by Guyer et aL [1]. I would like to make two comments. First, whenever a new sign is described [2], it is essential to calculate not only its sensitivity, but also its specificity and, preferably, its positive predictive value. The two latter factors could not have been estimated in Guyer et al.'s study unless malignant lesions were included. Without demonstrating that a sign is absent or rare in malignant lesions, it cannot be affirmed that the sign suggests that a lesion is benign. The second comment is that the authors had the prior knowledge that all lesions included in the study were benign and that could have opened the door for observer's bias. I have reviewed the breast ultrasound findings of 13 lesions which had histopathological proof. T h e ultrasound images were displayed in a random order with the patient's identification masked to avoid observer's bias. The sign described by Guyer et al. was positive in four out of the ten benign lesions a sensitivity of 40%, the same as the one found by Guyer et al. However, at least one, and possibly two, of the three malignant lesions (33% 66%) also showed the sign. Admittedly the numbers are small, but my findings suggest it is possible that this sign may well have a low specificity. A. M. A. H U S I E N
SIR I thank Dr Ozbek for the comments on my article. I agree that colour Doppler imaging is superior to conventional duplex Doppler ultrasound in identifying small arteries in the kidney and I think that colour Doppler imaging will be helpful in saving time for the acquisition of Doppler spectrum. I also agree with him that the signal-to-noise ratio is low at Doppler angles greater than 60°; however, I do not agree that Doppler indices, including resistive index which I used in my article, are not angleindependent when the Doppler angle is greater than 60 °. At Doppler angles greater than 60 °, the higher range of error in Doppler spectral analysis is not because of angle-dependence of the indices but is due to lower signal-to-noise ratio. Using conventional duplex Doppler ultrasound, in my experience, it is not difficult to obtain Doppler waveforms with adequate signal-tonoise ratio in the areas of the arcuate or the interlobar arteries of the kidney with audiovisual assistance. - -
S. H. K I M
Department of Diagnostic Radiology Seoul National University Hospital 28 Yongon-dong Chongnu-gu Seoul 110-744 Republic of South Korea
References
Breast Screening Unit Kettering General Hospital Kettering Northants NN16 8UZ
1 Guyer PB, Dewbury KC, Rubin CM, Butcher C, Royle GT, Theaker J. Ultrasonic attenuation in fibroadenoma of the breast. Clinical Radiology 1992;45:175-178. 2 Gardner M J, Altman DG. Statistics with confidence. British Medical Journal, London 1989:97-99. SIR Thank you for letting me see Dr Husien's letter in response to the publication o f our paper on fibroadenomas. All we set out to do was to alert colleagues to the echo-bright zone between the fibroadenoma and the accompanying attenuating shadow, and all that we claimed was that this 'might' be a sign to point towards a benign diagnosis. We feel that the numbers are too small to attempt any reasonable statistical analysis. - -
P. B. G U Y E R
Department of Radiology Royal South Hants Hospital Graham Road Southampton S09 4PE
