Cardiac sarcoidosis PET-CT | Super Sahyog Nuclear Imaging

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For most essential points to best prepare for the procedure, please download the patient information brochure (PDF).
For a more elaborate explanation of the procedure and related points, please continue to read ahead.

Brief introduction

Principle

Sarcoidosis is a condition wherein abnormal deposits of inflammatory cells called 'granulomas' are formed. Sarcoidosis can occur in any part of the body. In some cases, it can occur at disparate sites in the same person.

Cardiac sarcoidosis involves abnormal deposits in various parts, most notably in the junctional-conduction tissue, myocardium, papillary muscles, pericardium and coronary arteries. Manifestations depend upon the site of involvement.

Site of involvement	Abnormality
Junctional tissue	Arrhythmias
Myocardium	Altered contractility
Papillary muscle	Valvular disorder
Pericardium	Pericardial effusion (impaired heart contractility)
Coronary arteries (rare)	Coronary artery disease and ischaemic heart disease

Fluorodeoxyglucose (FDG) is a radioactive molecule that behaves similarly to glucose. Activated macrophages (type of inflammatory cells found in granulomas) use glucose at a very high rate, and thus concentrate FDG avidly.

Cardiac sarcoidosis is often suspected circumstantially, and its definitive diagnosis is difficult. Even taking a biopsy from the endocardium-myocardium can detect it only ~25% of times. Hence, corroborative findings from other investigations is very valuable in diagnosing cardiac sarcoidosis.

Treatment of sarcoidosis typically involves immunosuppressive drugs.

Indications (conditions in which advised)

FDG PET-CT for cardiac sarcoidosis is performed in following 3 settings.

In cases of proved extra-cardiac sarcoidosis as supporting evidence of cardiac sarcoidosis.
In cases of suspected cardiac sarcoidosis wherein biopsy would be negative or would not have been performed.
In cases of biopsy-proved cardiac sarcoidosis for baseline quantification of abnormalities, which in turn helps with assessment of response to treatment.

Considerations / steps before procedure

To have a most effective FDG PET scan for detecting sarcoidosis, it is important to make the cardiomyocytes switch to fatty acid utilization for energy production instead of glucose. To this end, 2 principles are to be followed: a high fat-low carbohydrate diet, and prolonged fasting.

Keeping these principles in mind, following are the dietary recommendations (to be followed for 24 hours before the scan).

Have 2 meals of high fat (with at least 35 g fat in each meal). Those consuming meat / eggs could have them fried in oil or butter, but without adding any kind of cereals (like rice or wheat) or cheese, paneer, etc. Those not consuming meat could have ~35 g ghee or butter along with tea or coffee. Amount of carbohydrates must be restricted to < 3 g in each meal.
Prolonged fasting (of 18 hours or longer) must be attempted.
Type II diabetes patients should skip insulin for 24 hours before the scan. However, it is important to get in touch with the doctor managing patient's diabetes to ensure safety.
Type I diabetes patients will need to continue (preferably, long-acting) insulin, but avoid rapid-acting forms. However, it is important to get in touch with the doctor managing patient's diabetes to ensure safety.

Other aspects of preparation for the procedure are identical with that of FDG whole-body FDG PET-CT, and are outlined below.

Prior appointment is a must as FDG spontaneously decays, and is not readily available at the diagnostic facility.
Patient must not be pregnant.
If breast feeding, please inform the staff for further directions.
Fasting blood glucose level should be preferably lower than 200 mg/dL. If the level is higher, please consult the doctor managing your diabetes.
Recent (within past 7 days) serum creatinine level must be known.
No diabetes related drugs (oral medications or insulin) for 6 hours before scan.
Avoid strenuous exercise for 1 day.
Please let the staff know at the time of appointment if the patient is unable to lie still for ~20 min, has breathing difficulty, or might need special medical attention for the duration of visit.
Have at least 1/2 litre water within an hour before reporting for the scan. There is no need to hold urine.
There is no need to hold urine before reporting for the procedure.
Wear loose-fitting but warm clothes.
Do not bring expensive jewellery or accessories along with you for the scan.
Proof of doctor's request is necessary for starting the procedure.
The patient must be accompanied by a responsible carer.

What to expect as part of procedure?

Important steps

Patient registration and consent.
Handing over medical documents to the staff.
Blood glucose level is measured through finger prick method.
Oral contrast (typically 500 to 1,000 mL) to be had over next 45 min to 1 hour.
Intravenous (IV) access is established (in form of cannula).
FDG is injected through the cannula. Some patients might receive unfractionated heparin 15 min before FDG injection.
Waiting time of ~1 hour (± 15 min) to allow sufficient time for FDG to be taken up and eliminated by all organs. Pass urine just before the scan, and also before that (if needed).
‘Whole-body’ procedure typically includes scanning from head to upper thigh as the patient lies still on their back. IV contrast is injected through the cannula. Time taken on the scanning table is ~15 min. Patient may have to hold breath for few seconds.
Scan is briefly reviewed for adequacy and quality. Occasionally, a scan may be repeated or scanning of additional body parts may be considered. If everything is to staff’s satisfaction, then the patient may leave.

Discomfort / risks during procedure

Pain during IV cannula insertion.
There is risk of extravasation at the time of IV cannula insertion, FDG injection or injection of iodinated IV contrast. [Extravasation means that blood leaks through the walls of vein punctured by cannula’s needle].
Iodinated contrast is injected in relatively large volumes and at a high flow rate. This can cause sensation of warmth and pain at the injection site. Rarely, patients develop allergic reaction to the contrast in form of skin rash, breathing difficulty, dizziness, or loss of consciousness. IV contrast also mildly and transiently suppresses kidney function, but it usually recovers completely by itself, and patients do not experience any corresponding discomfort.
FDG does not cause any discomfort. It is injected in very minute quantity, so it does not alter function of any organ.

Time taken for the entire patient visit

Typical: 3.5 hours.
Be prepared for: 5 hours (can be further prolonged in case of increased blood glucose level or other unforeseen events like malfunctioning of scanner, delayed delivery of FDG, etc.).

What to expect after procedure?

Precautions / special care

Maintain at least 1 metre-distance from pregnant ladies and children (below 10 years) for at least 5 hours after the scan.
Drink plenty of water throughout the day (3 to 4 litres).
Pass urine as frequently as possible.

Discomfort / risks

Because of IV contrast, some patients experience headache or heaviness of head, which resolve within a day.
Oral contrast can cause watery motions or loose stools. This typically resolves by itself within a day.
Both FDG and X-rays expose the patient to ionizing radiation. However, radiation dose received as part of the entire procedure is not expected to cause any obvious harmful effect. Additionally, benefit from information received through the procedure greatly outweighs any theoretical risk associated with this radiation exposure.

Time taken for report generation

Typical (for self-paying patients): 12 hours.
Be prepared for: 36 hours (especially if some patient data or past scan data are missing).
Credit patients will receive their reports from the respective referring hospitals.

Additional reading

For additional information, please visit the following links.

FDG PET-CT for cardiac sarcoidosis

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