&gt;Making a photo sensor must be thousands of times more complicated than ultrasounds sensors.<p>Cheaper thermal imaging sensors like that usually use a very, very low resolution sensor for picking up thermal data, then use interpolation to map the low-resolution data onto a high-resolution image provided by a higher-res conventional camera sensor. Obviously, this approach won&#x27;t work with ultrasound tech, as there wouldn&#x27;t be a secondary high-resolution data source.