SPECT-CT Scan

Authors: Dr Geoffrey Soo*
                    Dr Timothy Cain *
                    Dr Chian Aun Chang *

What is a SPECT-CT Scan?

A SPECT-CT scan is a type of nuclear medicine scan where the images or pictures from two different types of scans are combined together. The combined scan can provide precise information about how different parts of the body are working and more clearly identify problems.

Single-photon emission computed tomography (SPECT):

SPECT images are taken after an injection of a nuclear medicine radiopharmaceutical (see InsideRadiology: Nuclear Medicine). The injected medication ‘sticks’ to specific areas in the body, depending on what radiopharmaceutical is used and the type of scan being carried out. For example, it can show bone in a bone scan, and gall bladder and bile ducts in a hepatobiliary scan.

The radiopharmaceutical is detected by nuclear medicine gamma cameras. The camera or cameras rotate over a 360-degree arc around the patient, allowing for images to be reconstructed in three dimensions.

Computed tomography (CT):

CT images are initially obtained while the patient is lying on a bed that moves into a ring- or ‘donut’-shaped X-ray machine. The X-ray machine rotates over a 360-degree arc around the patient, allowing for images to be reconstructed in three dimensions. The X-ray machine from the CT scanner rotates much faster than the gamma camera, so the CT part of the scan takes less time than the SPECT scan.

What are the benefits of a SPECT-CT scan?

The similarity between SPECT and CT in the method of processing the images allows the images to be merged and the information to be combined. Combining the information from a nuclear medicine SPECT scan and a CT scan allows information about body ‘function’ from the nuclear medicine scan to be easily combined with the information about where and how the body structure ‘looks’ in the CT scan.

Why would my doctor refer me to have this scan?

Common reasons include joint or bone pain, fracture and arthritis assessment, blood flow to the heart, and blood flow to the lungs.

Where is a SPECT-CT scan done?

A SPECT-CT scan is done at a nuclear medicine facility with a dedicated SPECT-CT machine. Many large public and private hospitals, as well as some private radiology practices, now have SPECT-CT scanners.

How do I prepare for a SPECT-CT scan?

A SPECT-CT scan is usually done at the same time as other types of scans that use a nuclear medicine gamma camera, so no extra preparation is required for being imaged on a SPECT-CT machine.

If you are pregnant, if there is a possibility you may be pregnant or if you are breast-feeding, it is important you inform staff at the hospital or radiology facility where you are having the scan. This scan may not be suitable for pregnant women because of the radiation dose to the growing foetus. Please discuss this with your doctor.

Women who are breast-feeding and those who are primary or sole carers of young children (under 5 years-of-age) may need to make special preparations before and after this scan. They have to stop breast-feeding and avoid close contact with young children for a short time, usually 24 hours. This is due to the small amount of radioactivity your body may release after the scan. Discuss this with your referring doctor and the nuclear medicine facility where you will have the scan for more details. The Australian Radiation Protection and Nuclear Safety Agency has recommendations about breast-feeding and close contact with children after nuclear medicine tests.

Who does the SPECT-CT scan?

Nuclear medicine technologists carry out the scans, which are then analysed and interpreted by nuclear medicine specialist doctors who also provide a report of the scan to your referring doctor. See Nuclear Medicine for more information about these health professionals.

What happens during a SPECT-CT scan?

After verifying your details and the reason for the scan, the nuclear medicine technologist will insert an intravenous (IV) cannula (a thin tube) into a vein, usually in your hand or arm. The radiopharmaceutical is injected into your blood stream through the IV cannula. You will then be required to lie on a bed while detectors or cameras obtain the scan images.

As part of the SPECT-CT, you are required to lie still in a ring shaped scanner for at least 30–40 minutes. The first 3–5 minutes involves the CT scan component, with the remainder of time required for the SPECT scan. It is very important that you remain still for the entire duration of the two scans, so that the SPECT and CT can be accurately combined. If you do not lie still, the images from one scan will not exactly correspond to the images from the other scan, and the combined scan may be difficult to interpret.

When you are positioned for the scan, please make sure you are in a position that will allow you to keep still. If you do not think you will be able to lie still for 30–40 minutes during the scan please tell your doctor or the nuclear medicine staff.

How long does a SPECT-CT scan take?

It takes 30–40 minutes to obtain the SPECT and CT images, then you are allowed to leave.

Are there any after effects of a SPECT-CT scan?

There are no after-effects from a SPECT-CT scan.

If you are breast-feeding or caring for young children, see the ‘How do I prepare for a SPECT-CT scan?’ section for more information about special precautions you have to take after the scan.

What are the risks of a SPECT-CT scan?

The scan involves a small dose of ionising radiation from the radiopharmaceutical injected into your vein, and also from the CT scan (see InsideRadiology: Radiation risk of medical imaging for adults and children).

Importantly, the SPECT scan requires no additional injection of radiopharmaceutical beyond what you would have been given for a standard nuclear medicine scan without SPECT. The CT is usually carried out using a low-dose radiation technique, which is approximately 20–25% the radiation exposure of a normal CT scan.

Your doctor has weighed up the benefits versus risks in having a SPECT-CT scan, and has decided that the benefit of having the information gained from the scan outweighs any risk.

When can I expect the results of my SPECT-CT scan?

A radiologist or nuclear physician (specialist doctor who is trained to interpret the images obtained) will read your images and write a report. This is usually done in a few days or a week from the time of your scan. The report is then sent to your doctor who referred you for the scan. The time it takes your doctor to receive a written report on the scan will vary depending on:

• the urgency with which the results are required by your doctor;
• whether more information is needed from your doctor before the test or procedure can be interpreted by the radiologist or nuclear physician (specialist doctors);
•  whether you have had previous X-rays or other medical imaging that need to be compared with this scan (this is commonly the case if you have a disease or condition that is being assessed as to its progress);
• how the report is sent to your doctor (i.e. phone, email, fax or mail).

The radiology facility where you are having the scan will be able to tell you when the written report will be provided to your doctor.
It is important that you discuss the results with your doctor, either in person or on the telephone, so that they can explain what the results mean for you.

*The author has no conflict of interest with this topic.

Page last modified on 19/12/2019.