One of the features people most love about the Elite 5600 and ScanPad is that you can change the colour map, so that your entire image takes on a different hue. This feature (photopic imaging) is present on many ultrasound machines, and is commonly used in certain specialties. I perform a lot of cardiac ultrasound and if an echocardiographer is scanning a patient in whom a thrombus (blood clot) is suspected, we will frequently use a sepia colour map in order to help us spot the often very subtle differences in echogenicity between a thrombus and the heart wall.
Another popular application among our veterinarian and vet nurse clients is small animal pregnancy detection, particularly during early pregnancy in dogs and cats. The sepia colour can really make gestation sacs ‘pop’ in a way that standard greyscale imaging does not; but, is there any science to back this observation up?
The way we perceive colour varies between individuals, but evidence that colour maps make a significant difference to accuracy of ultrasound image interpretation is lacking in many fields. In echocardiography, despite its widespread use when looking at impaired ventricles or searching for clots, only a weak correlation has been found between the use of a colour map, and accuracy of left ventricular systolic function estimates (Huang et al., 1991). Nobody appears to have revisited the issue in over 30 years.
When it comes to head and neck imaging, however, the Germans have been leading the way (Fischer et al., 2002; Kothe & Schade, 2003), demonstrating that colour maps do improve diagnostic accuracy and the ability to spot pathology, particularly when combined with tissue harmonic imaging (THI). THI is a feature that is present on the ScanPad, as well as higher specification machines like the Apogee 1000 Lite. Lin et al. (2003) have also found photopic imaging to significantly improve image contrast in musculoskeletal applications.
I would assume that the reason no significant improvement of image interpretation with photopic imaging has been found in my own field of cardiac ultrasound is that the investigators were studying the wrong thing. Colour maps don’t significantly improve estimations of left ventricular systolic function, but then, that’s rarely what they’re used for, anyway. Findings from other fields of ultrasound have found that the real strength of photopic imaging is where contrast resolution is low, and this is precisely when it tends to be used in echocardiography: to differentiate thrombus from endocardium.
What about pregnancy scanning?
Just as in cardiac ultrasound, the research on colour maps is lacking when it comes to pregnancy detection. However, experience among our client base seems to suggest that a sepia colour map in particular is helpful in detecting pregnancy in difficult subjects, such as overweight canines or in sheep or goats. It’s also a popular feature for many of our clients simply because it makes their images stand out to their clients.
Do you scan in grey scale, or do you use colour? We’d love to hear your experiences! Send us a message, or chat to us on Facebook.
Fischer et al. (2002). Image quality and detection of pathology by ultrasound: comparison of B-mode ultrasound with photopic imaging and tissue harmonic imaging alone and in combination.
Huang et al. (1991). Comparison of gray-scale and B-color ultrasound images in evaluating left ventricular systolic function in coronary artery disease.
Kothe, C., Schade, G. (2003). Preliminary experiences with Photopic ultrasound imaging in the head and neck region.
Lin et al. (2003). Advantages of photopic imaging in sonography of low contrast musculoskeletal lesions and structures in the foot