Work is well under way on phase two of the Community Diagnostic Centre at Southlands Hospital.
The Shoreham hospital opened the centre last October and has treated more than 27,000 patients so far.
At the moment it has CT and MRI scanners, as well as advanced X-ray rooms.
The new phase will offer additional services including echocardiography, gynaecological and respiratory procedures.
It is expected to be complete by the autumn.
READ MORE: Diagnostic centre set to expand and treat even more patients
The centre, which can offer diagnostic services outside busier hospitals, has improved patient care.
By providing scans to the public closer to home it has helped to reduce waiting list times by offering appointments more quickly.
It also means people are not as much at risk of cancellations as they are in busier hospitals.
A spokesman for University Hospitals Sussex NHS Foundation Trust, which runs the hospital, said: "Our colleagues got an exciting sneak peek into phase two of our Community Diagnostic Centre at Southlands.
"Phase two will house further diagnostic services, including echocardiography, gynaecological and respiratory procedures so it was only fitting to give colleagues from these specialties a behind-the-scenes look at the progress being made.
"Colleagues were able to see their new workspace and begin to plan how best they can utilise this space to suit the needs of their patients.
"Work is expected to be finished in autumn and once complete, the CDC will embody a true ‘one-stop’ model of care, enhancing efficiency and further improving the overall patient experience for people in Sussex."
The hospital trust said the multimillion-pound centre is a "game-changing" investment for Sussex.
Another centre opened in Bognor earlier this year with CT and MRI scanners. It saw 100 patients within its first week of opening.
The Amex Football Stadium in Falmer also has a CDC facility for patients to access scans and tests.
These centres are all part of a national government plan to speed up access to potentially lifesaving tests and checks.
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