The present invention relates to a method and system for diagnosing blood vessel obstruction, such as would occur in deep vein thrombosis (DVT). More specifically, the present invention relates to a software tool for use with sensor hardware to allow users to perform standardised and repeatable testing of patients to assist with diagnosis of deep vein thrombosis or related conditions. The present invention further relates to an apparatus and method for conducting the diagnosis. According to a first aspect of the present invention, there is provided an apparatus for diagnosing whether a blood vessel is obstructed, comprising: an interface for communication with an imaging device which imaging device comprises a transmitter and a receiver,a user interface, and a processor, which processor is programmed to perform the following steps: inform the user, via the user interface, where to place the imaging device on a patient's body, instruct the imaging device to transmit radiation from the probe, receive reflected radiation from the imaging device,interpret the reflected information fully automatically using a learned algorithm, determine from the reflected radiation whether the imaging device is located correctly relative to a blood vessel of the patient,inform the user, if the imaging device is not located correctly, to reposition the imaging device and to repeat the instruct, receive and determine steps until the imaging device is correctly located,inform the user to apply pressure to the patient's blood vessel using the imaging device,instruct the imaging device to transmit further radiation, receive further reflected radiation from the imaging device, and determine from at least the reflected further radiation whether the blood vessel is obstructed. The system may be arranged to work with any other real-time imaging device by retraining and/or relabelling of new images. It may also work with other non-real-time methods, for example CT and MRI. For example, with a pre
