Positron Emission Tomography (PET) scans are a vital tool for medical professionals, particularly in cancer detection. These scans rely on the body's glucose consumption to identify areas of increased metabolic activity, indicative of disease. To ensure accurate PET scan results, following a specific low-carb diet protocol is crucial. This article provides a detailed guide on the low-carb diet protocol for PET scans, including dietary guidelines, pre-scan instructions, and other essential considerations.
Understanding the Role of Diet in PET Scans
PET scans detect signs of high glucose consumption by cells. Typically, glucose speeds up the growth of cancer cells, which is why doctors inject glucose into the patient's body when performing the scan. Because the scan uses radioactive sugar as a tracer, consuming sugar can interfere with the test results. "Sugar” doesn’t just mean foods and beverages that taste sweet or have added sugar, but also lots of foods contain sugar and starches, which break down into sugar. Therefore, adjusting to a low-carb, no-sugar diet 24 hours before your PET scan is necessary.
Dietary Guidelines for PET Scan Preparation
When it comes to PET scan preparations, your physician will advise you to follow a strict diet that is low in carbohydrates. The goal of this diet is to ensure the stability of glucose levels in your body. Here's a breakdown of what to eat and what to avoid:
Foods to Eat
Actually, you are not required to stay hungry before a PET scan. Some of the foods you can eat are those that are rich in protein content. High protein, low carbohydrate diet ensures the stability of glucose levels in your body. Therefore, you can eat:
- Steak
- Chicken
- Fish
- Eggs
- Duck
- Cheese
- Turkey
- Asparagus
- Mushrooms
- Broccoli
Foods to Avoid
Foods that are high in carbohydrate content and low in protein content must be avoided. This is because such foods can throw your body’s glucose levels out of balance and lead to inaccuracies in results. Examples of foods that have high carb content are:
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- Pasta
- Potatoes
- Rice
- Waffles
- Oatmeal
- Raisins
- Bagels
- Bread
Some of the other foods that can impact the results of a PET scan are sugar, caffeine, and tobacco. Therefore, these foods are best avoided.
Detailed Pre-Scan Instructions
Preparing for a PET scan requires following some essential steps in the lead-up to the procedure. Your medical team will give you precise instructions, but this guide can give you a general idea of what to expect.
24 Hours Before the Scan
- Low-Carb, No-Sugar Diet: Experts advise adjusting to a low carb, no-sugar diet 24 hours before your PET scan.
- Avoid Alcohol, Tobacco, and Caffeine: In addition to adjusting your diet, you’ll need to avoid alcohol, tobacco, and caffeine.
- Refrain from Vigorous Exercise: You’ll also need to refrain from vigorous exercise for 24 hours before your scan. Strenuous activity beforehand can cause your body to absorb the tracer more quickly.
6 Hours Before the Scan
- Fasting: Experts recommend that you stop eating and drinking for 6 hours before a PET scan. The exact number of hours may vary depending on your medical team. However, you can drink water during this period. It will be important to stay hydrated.
- Medications: Routine medications may be taken, unless you have been instructed otherwise. People with diabetes may have special instructions regarding medications. Any non-diabetic medications may be taken the day of your scan.
Day of the Scan
- Hydration: It is important that you stay well hydrated.
- Clothing: If possible, do not wear clothing with belts, zippers, snaps or metal of any kind to your appointment. You’ll want to wear loose, comfortable clothes without any metal parts, such as zippers, buttons, or buckles. Some places may have you change out of your clothes into a hospital gown. If you wear glasses, you’ll need to remove them for the scan. You’ll also need to remove jewelry and other metal objects. Try to stay warm on the day of your scan.
- Arrival: Most places request that you check in 15 to 30 minutes early for your appointment. Arriving on time is important, as the radioactive tracer can only work briefly.
- Blood Glucose Level Test: The team will test your blood glucose level. We are looking for your blood glucose level to be between 70mg/dL and 200mg/dL.
- Contrast Injection: Commonly, contrast is injected into a vein to better define the images throughout the body. If the radiologist believes this is helpful, a small intravenous (IV) line is placed in an arm vein. Through this line, the contrast and the isotope will be injected. After the injection you may be given one cup of an oral barium contrast to drink.
- Rest: You will rest quietly in a reclining chair for 75 minutes.
Special Considerations
- Pregnancy and Breastfeeding: As soon as a doctor schedules a PET scan, let them know if:
- You are or might be pregnant: Radioactivity can affect the fetus. If the PET scan is medically necessary, the radiology team may need to make special considerations.
- You are breastfeeding or chestfeeding: This may influence which type of radioactive tracer they use in the scan. Otherwise, they may reschedule the scan.
- Diabetes: You have diabetes: Your doctor may need to adjust your diabetes medication dosage because blood sugar levels can affect the scan.
- Anxiety and Claustrophobia: Anxiety can affect PET scan results, so let your medical team know if you’re feeling anxious about the test or if you have claustrophobia. Though sedatives can also affect PET scan results, the doctor may be able to administer a mild one to help you relax.
- Adverse Reactions: If you feel any symptoms such as nasal congestion, itchy eyes, hives, rashes, sneezing, restlessness, tremors, pain, nausea, vomiting, dizziness, please notify the staff immediately. The staff is prepared to handle these situations. If you feel any of these symptoms after you have left the department, please contact your doctor or go to the nearest emergency room.
Understanding the PET Scan Procedure
Positron emission tomography, also called PET imaging or a PET scan, is a diagnostic examination that involves getting images of the body based on the detection of radiation from the emission of positrons. You will rest quietly in a reclining chair for 75 minutes. The scan will take 45 minutes to 2 hours, but the results could take weeks. If your results come back quickly or take a long time, it’s helpful not to make assumptions about what that time frame means.
The Importance of Myocardial Suppression
Assessment of increased glucose uptake in inflammatory or malignant myocardial disease using PET/MRI relies on uptake suppression in normal myocardium. In a study, PET/MRI was successfully performed in 89 patients. HFLCPP (High Fat Low Carbohydrate Protein Protocol) was started ≥24 hours prior to PET/MRI. All patients received i.v. injection of unfractionated heparin (50 IU·kg-1) 15 minutes prior to FDG administration. Left ventricular FDG uptake was visually evaluated by two readers. Diffuse myocardial uptake exceeding liver uptake, isolated uptake in the lateral wall, or diffuse uptake in the entire circumference of the heart base were defined as failed suppression. Success rate was 84%. Suppression was unsuccessful in 14 patients. No significant influence of gender (P = .40) or age (P = .21) was found. However, insufficient suppression was more common in patients younger than 45 years (20% vs 7%).
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