SPECT CT scan
What is an SPECT-CT scan?
SPECT-CT is where two different types of scans are taken and the images or pictures from each are fused or merged together. The fused scan can provide more precise information about how different parts of the body function and more clearly identify problems such as fractures etc.
Single photon emission computed tomography (SPECT):
SPECT images are obtained following an injection of a radiopharmaceutical that is used for nuclear medicine scans. The injected medication sticks to specific areas in the body, depending on what radiopharmaceutical is used and the type of scan being performed, for example. it will show bone for a bone scan, and gall bladder and bile ducts for a hepatobiliary scan.
The radiopharmaceutical is detected by a nuclear medicine gamma camera. The camera or cameras rotate over a 360 degree arc around the patient, allowing for reconstruction of an image in three dimensions.
Computed tomography (CT): CT images are obtained while you lie on a bed that moves into a ring, or "doughnut" shaped X-ray machine. Again, the X-ray machine rotates over a 360 degree arc around the patient, allowing for image reconstruction in three dimensions. The X-ray machine from the CT scanner rotates much faster than the gamma camera, so the CT part of the study takes less time than the SPECT study.
The similarity between SPECT and CT in the method of image processing allows the images to be combined. Combining the information from a nuclear medicine SPECT study and a CT study allows the information about function from the nuclear medicine study to be easily combined with the information about how the body structure "looks" in the CT study.
What happens during a SPECT-CT Scan?
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 is required for the SPECT study. It is very important that you remain still for the entire duration of the two studies so that the SPECT and CT can be accurately combined. If you do not lie still, the images from one study will not exactly correspond to the images from the other study, and the study 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 inform your doctor or the nuclear medicine staff.
How do I prepare for an SPECT-CT scan?
No extra preparation is required.
It is important that you let staff at the hospital or radiology practice where you are having the scan done know if you are (or think you could be) pregnant or are breast feeding.This study 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 breastfeeding and people who are the primary or sole carer for small children may need to make special preparations for after the test, to stop breastfeeding for a short time, and to avoid close contact with young children. This is due to the small amount of radioactivity your body may release for a while after the test. Talk to your referring doctor or the nuclear medicine practice where you will have the test for details. The Australian Radiation Protection and Nuclear Safety Agency has recommendations about breastfeeding and close contact with children after nuclear medicine tests.
Are there any after effects of an SPECT-CT Scan?
There are no after-effects from a SPECT-CT scan.
However, if you are breastfeeding or caring for young children, see the “how do I prepare” section for more information about special precautions you may need to take.
How long does an SPECT-CT Scan take?
The nuclear medicine injection takes approx. 15 minutes and then you can leave the department and return 2 hours later. The nuclear medicine scan will take 30 minutes - 1 hour. Once this scan is complete your CT scan will take 15 minutes and your images will be merged.
What are the risks of an SPECT-CT Scan?
There are no risks involved in the nuclear medicine SPECT scan or the CT scan procedures. The test involves a small dose of ionising radiation from the radiopharmaceutical injected into your vein, and also from the CT scan. (See Radiation Risk of Medical Imaging for Adults and Children)
Importantly, the SPECT component of the test requires no additional injection of radiopharmaceutical beyond what you would have been given for the nuclear medicine test without the SPECT part. Your doctor has weighed up the benefit versus risk for having a SPECT-CT scan and has decided that the benefit of having the information gained from the scan outweighs any risk.
What are the benefits of a SPECT-CT Scan?
SPECT-CT provides the ability to merge or combine the images often allowing the nuclear medicine specialist to more accurately pinpoint the site of any abnormality on your nuclear medicine scan. This may be of particular importance in certain clinical situations, when the interpretation of an area of interest may change depending on its location. For example, in small areas like the spine or feet, it is sometimes hard to determine from the nuclear medicine imaging alone whether the abnormality lies in the bone or the adjacent joints – fusing a SPECT with CT provides added confidence in identifying where the abnormality is.
Who does the SPECT-CT Scan?
Nuclear medicine technologists perform the scans which are then analysed and interpreted by nuclear medicine specialist who also provide a report of the scan to your referring doctor. See Nuclear Medicine for more information about these health professionals.
How do I get my results?
Your doctor will receive a written report on your test as soon as is practicable.
It is very important that you discuss the results with the doctor whom referred you so that they can explain what the results mean for you.
This information is credited to Inside Radiology, Royal Australian and New Zealand College of Radiology (RANZCR).
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