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Adrenal Lesions: Attenuation Measurement Differences between CT Scanners¹

¹ From the Department of Radiology–White 270, Massachusetts General Hospital and Harvard Medical School, 55 Fruit St, Boston, MA 02114. From the 2004 RSNA Annual Meeting. Received December 14, 2004; revision requested February 7, 2005; revision received July 7; accepted August 2; final version accepted October 25. Address correspondence to P.F.H. (e-mail: phahn{at}partners.org).

Purpose: To retrospectively compare unenhanced computed tomographic scans of the same adrenal lesion obtained with two different manufacturers' multidetector scanners to assess whether there are differences in attenuation measurements.

Materials and Methods: The study was approved by the local ethical committee, which waived patient consent, and was conducted in compliance with HIPAA. Electronic searching revealed patients with adrenal nodules scanned with both a Siemens 16–detector row scanner and one of eight GE Medical Systems multi–detector row scanners between January 2000 and September 2004 without the use of intravenous contrast material. Lesions were characterized by using histologic findings, fat content, or size stability. Size stability for 6 months was required unless both scans were obtained within 21 days of each other. Two radiologists independently measured lesion attenuation for regression analysis. Lesions considered benign (10 HU) on one scan and indeterminate (>10 HU) on the other were separately analyzed, and technical parameters of scanning were compared.

Results: There were 47 patients (27 men, 20 women; age range, 40–86 years; mean age, 64 years) with four metastases, 42 adenomas, and one myelolipoma (long-axis length, 10–85 mm; mean, 24 mm). GE scans were obtained with four–detector row scanners (n = 32), an eight–detector row scanner (n = 2), and 16–detector row scanners (n = 13). Correlation between the two readers was 0.99 for both Siemens and GE scan attenuation measurements. The slope of regression lines for both readers plotting GE attenuation (y-axis) against Siemens attenuation (x-axis) was less than 1, which indicated a slight but statistically significant tendency for GE scans to have lower attenuations than do Siemens scans. For both readers, there were more lesions indeterminate (>10 HU) on Siemens scans but benign (10 HU) on GE scans than the reverse (McNemar test, P < .02 for reader 1, not significant for reader 2). Average Siemens and GE scan technical parameters were similar.

Conclusion: There are only slight differences in attenuation of adrenal nodules measured on scans obtained with different scanners.

© RSNA, 2006

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