Which of the following techniques preserves pixel density when enlarging the image?

Write magnification is the correct technique that preserves pixel density when enlarging an image in ultrasound. This method involves acquiring the original image at a higher resolution before enlarging it, which ensures that the detail and clarity are maintained even as the image is scaled up. The ultrasound system processes the data from a region of interest (ROI) with increased pixel density, thus preventing any loss of spatial resolution that can occur during enlargement.

In contrast, post-processing and zoom magnification typically enlarge images after they have already been captured, which can lead to a decrease in pixel density and potentially reduce image quality. While post-processing allows for manipulation of the images after they are acquired, it does not provide the same level of detail retention as write magnification. Image interpolation works by estimating pixel values based on surrounding pixels, which can help in creating a larger image but does not genuinely increase the original data density. This technique may improve the appearance of an image but does not maintain the same fidelity as write magnification, leading to potential artifacts and less accurate representation of the ultrasound data.