Editor:
We congratulate Dr Hoffman and his team for their beautiful and important article published in the June 2009 issue of Academic Radiology . This article highlights an important topic for emphysema measurement. However, in their paper, the authors state, “Based on pathology comparisons…and literature-based consensus…−910 HU [Hounsfield units] was specified a priori as the threshold for primary analyses.” A threshold of −910 HU was established by Müller et al , who used one single-slice computed tomographic scan with a slice thickness of 10 mm and intravenous contrast. Slice thickness and the use of intravenous contrast influence lung density and the measurement of emphysema . Recently, Madani et al reported a study using multidetector computed tomography without iodinated contrast. The strongest correlation of multidetector computed tomography with macroscopy was observed at a threshold of −970 HU ( r = 0.543, P < .001), and that with microscopy was observed at −960 and −970 HU. We would like to know Hoffman et al’s rationale for choosing a threshold of −910 HU.
References
1. Hoffman E.A., Jiang R., Baumhauer H., et. al.: Reproducibility and validity of lung density measures from cardiac CT scans—the Multi-Ethnic Study of Atherosclerosis (MESA) Lung Study. Acad Radiol 2009; 16: pp. 689-699.
2. Müller N.L., Staples C.A., Miller R.R., Abboud R.T.: “Density mask.” An objective method to quantitate emphysema using computed tomography. Chest 1988; 94: pp. 782-787.
3. Madani A., De Maertelaer V., Zanen J., Gevenois P.A.: Pulmonary emphysema: radiation dose and section thickness at multidetector CT quantification—comparison with macroscopic and microscopic morphometry. Radiology 2007; 243: pp. 250-257.
4. Adams H., Bernard M.S., McConnochie K.: An appraisal of CT pulmonary density mapping in normal subjects. Clin Radiol 1991; 43: pp. 238-242.
5. Madani A., Zanen J., de Maertelaer V., Gevenois P.A.: Pulmonary emphysema: objective quantification at multi-detector row CT—comparison with macroscopic and microscopic morphometry. Radiology 2006; 238: pp. 1036-1043.