PET Center


 
PET/CT

PET/CT

Technical information

The integration of positron emission tomographie (PET) with computer tomographie (CT) has a long tradition in our department. One of the first scanner combining the two imaging modalities for clinical studies was installed in March 2001 in our clinic. Since then PET/CT is an established imaging method world wide. In Switzerland every university hospital and most of the large clinics have a PET/CT (a total of 30-35 scanners in Switzerland).

The main principle of PET imaging is the detection of radioactive decay within the body. Injected radiotracers will decay and emits two photons, with multiple detector rings surrounding the patient this decay can be localized. The great advantage of PET over conventional radiological imaging modalities such as CT or MRI is the high sensitivity for the injected substances. This allows the visualization of biochemical processes and therefore enables the detection of lesions before anatomical changes can be detected. Thanks to a relatively short half-life of the used isotopes (18F = 110 min, 68Ga = 68 min), the exams have a low radiation burden to the patients. However it forces us to stick to a fixed time schedule, since any delay leads to a decrease in tracer activity. 

Depending on the tumor subtype, different tracers are used for PET/CT imaging (18F-FDG, 18F-Cholin, or 68Ga-DOTATATE). 

18F-FDG PET/CT:

18F-FDG is the most commonly used tracer in PET imaging today. It consists of a modified and radioactive labeled sugar. After the injection into the body, 18F-FDG accumulates in all cells with a glucose uptake such as the brain, the heart, tumors and metastasis. 

Bild1.png
 

 

           
Figure 1

Preparation and scanning:
It is mandatory that patients are fasting for at least 4 hours prior to a 18F-FDG scan. No food, no sweets such as candies or chewing gums shall be consumed, even if they are sugar free. Only water or teas without sugar can be taken, together with the daily medication. Any stimulation of insulin production could interfere with the image quality. Medication that has be taken together with food, should be taken either 4h before the scan or after the exam.
After the injection patients are asked to rest for 50-60 minutes, so that the tracer can distribute in the body and does not accumulate in the muscles. After this the images are acquired (20-25 min).

18F-FDG PET/CT and diabetes?
High blood sugar values are reducing the image quality substantially. Therefore patients suffering from diabetes mellitus have to be careful regarding their blood sugar values before the scan. For the examination the blood glucose level must be under 12 mmol/l, ideally under 7 mmol/l. Ideally glucose values are checked the day before the FDG PET/CT and if there is any difficulty the PET team should be informed (Tel: 044 255 35 72). If not instructed otherwise you can consider the following roles:

Typ I diabetes:
- With insulin (base / bolus): Take the regular base insulin in the evening, have a little breakfast and the regular bolus insulin early in the morning (before 7) and come to the scan around noon (after 11 am).
- If you have a continuous insulin pump, leave it on “night setting” the morning before the scan. Do not eat any breakfast or inject bolus insulin. The scan should be done in the early morning.
 
Typ II diabetes:
- You can take oral antidiabetics together with food, if it is at least 4 hours before the scan.
- Blood sugar will be checked before every scan.

18F-FDG PET/CT and renal insufficiency?
18F-FDG PET/CT can be performed even if the kidney function is impaired without risk of side effects. However, if the kidney function is reduced no contrast enhanced CT scan will be performed.

18F-FDG PET/CT during pregnancy or breast feeding?
Due to the radiation burden to the child a 18F-FDG PET/CT will not be performed during pregnancy.
If a mother is breast feeding she should not directly breast feed the child fro 6h after the scan. The radioactive tracer does not accumulate in the milk, but in the breast tissue – therefore the milk does not have to be discharged but can be give to the baby with the buddle by someone else.

18F-FDG PET/CT risks and side effects?
For PET examinations only minimal amounts of tracer are necessary thanks to the high sensitivity of the detectors. Therefore any interaction with other medication or allergic reactions are not expected. Thanks to the short half-life of 18F-FDG the radiation burden to the patient is only slightly higher compared to a conventional CT (8-10 mSv).

18F-FDG PET/CT indications:
The following indications for 18F-FDG PET/CT have been established and are covered by the Suisse public insurance:
- Staging and re-staging or various cancers with increase glucose metabolism (lung, ENT-tumors, pancreatic or hepatic cancer, ovarian or cervical cancer, seminoma, esophageal or gastrointestinal carcinomas,...).
- Lymphoma
- High risk melanoma         
- Dementia

18F-Cholin PET/CT:

18F-Cholin PET/CT is a sensitive and very specific exam for patients with prostate cancer. In the case of a newly diagnosed high risk prostate cancer it will be used to rule out lymph node or distant metastasis. In patients previously treated for prostate cancer with a rising PSA it can be used for early detection of the recurrence and guide focal treatment.

Prostate cancer cells have an increase in Choline uptake over time, therefore we perform two scans for Choline PET to distinguish benign from malignant lesions.

Cholin.png

 

 Figure 2

Preparation and scanning:
Since the same transporters take up Choline and amino acids into the cell, we recommend that patients should not be eating for at least 4 hours.
The tracer injection in done on the scanner. First the whole body CT is acquired, than the early 18F-Cholin phase (2-17 min), directly followed by the late phase (20-35 min). The two time points allow a better distinction between inflammatory lesions (decrease in activity) and malign lesions (increase in activity).

18F-Cholin PET/CT and diabetes?
The 18F-Cholin PET/CT exam is not affected by a high blood glucose or increased insulin levels. Therefore no special preparation in necessary.

18F-Cholin PET/CT and renal insufficiency?
18F-Cholin PET/CT can be performed also with impaired renal function.

18F-Cholin PET/CT risk and side effects?
For PET examinations only minimal amounts of tracer are necessary thanks to the high sensitivity of the detectors. Therefore any interaction with other medication or allergic reactions are not expected. Thanks to the short half-life of 18F-Cholin the radiation burden to the patient is only slightly higher compared to a conventional CT (8-10 mSv).

18F-Cholin PET/CT indications:
Established indications and since the 01.07.2014 also reimbursed by the Swiss public insurance are the following indications:
 -     Staging for high risk prostate cancer.
- Re-staging patients with biochemical relapse after primary therapy. However good detection rates for tumor recurrence can be reached when either the PSA Level is > 2 ng/ml or the PSA doubling time is < 7.3 months. 

68Ga-DOTATATE PET/CT:

68Ga-DOTATATE PET/CT is the most sensitive exam to detect well-differentiated neuroendocrine tumors. Since these tumors have a low glucose consumption but high expression of somatostatine receptors (SSTR) on their surface, 68Ga-DOTATATE is superior to 18F-FDG for tumor detection. This new method has replaced the Octreotide scintigraphiy in our clinic, due to a higher sensitivity and an improved localization of the SSTR positive lesion, thanks to the CT component.

Dotatate.png

 


Figure 3

Preparation and scanning:

Patients should be fasting for at least 4 hours. Oral medication can be taken regularly. Sandostatine injections should always be performed after the 68Ga-DOTATATE PET/CT and not before.
To increase the detection rate of small lesions in the abdomen, an additional contrast enhanced CT is often required.

68Ga-DOTATATE PET/CT and diabetes?
The 68Ga-DOTATATE PET/CT exam is not affected by a high blood glucose or increased insulin levels. Therefore no special preparation in necessary.

68Ga-DOTATATE PET/CT and renal insufficiency?
68Ga-DOTATATE PET/CT can be performed also with impaired renal function.

68Ga-DOTATATE PET/CT während der Schwangerschaft & Stillzeit?
Due to the radiation burden to the child a 68Ga-DOTATATE PET/CT will not be performed during pregnancy.
If a mother is breast feeding she should not breast feed the child for 12h after the scan.

68Ga-DOTATATE PET/CT risks and side effects?
For PET examinations only minimal amounts of tracer are necessary thanks to the high sensitivity of the detectors. Therefore any interaction with other medication or allergic reactions are not expected. Thanks to the short half-life of 68Ga-DOTATATE the radiation burden to the patient is only slightly higher compared to a conventional CT (7-8 mSv).

68Ga-DOTATATE PET/CT indications:
Established and covered by most insurance companies are the following indication for 68Ga-DOTATATE PET/CT scans:
- Staging und re-staging of well differentiated neuroendocrine tumors.
- Therapy control
- Evaluation for potential 177Lu-DOTATATE therapy

PET/MR

Simultaneous PET/MR

The University-Hospital Zurich (USZ) is one of the few locations worldwide that offers state-of-the-art PET / MR imaging. In contrast to PET / CT, PET is combined and performed simultaneously with MRI. The latest PET / MR system was launched in January 2014, and together with two other universities in the USA (Stanford and UCSF) the USZ contributed to the market approval of this modality.
By carefully evaluating the data collected on the former PET / CT-MR system, rapid clinical indications could be identified, in which the PET / MR could bring a clinical advantage to the patients. In the meantime, not only scientific but also clinical experiences with the new modality have been established.

The above-mentioned measures with regard to preparation for the examination, measures for diabetes, pregnancy and lactation are generally also valid for the PET / MR.

The basic principle of PET corresponds to that in PET / CT (see above). Accordingly, the preparation does not differ. The advantage, however, is the simultaneous MRI, which in turn results in a dose reduction and is also more suitable for certain indications which require a higher soft tissue contrast than offered by CT:

Particularly in the examination of children (for example lymphoma, bone tumors), the aspect of the significantly reduced radiation is important, especially in view of the often repeated investigations.

In addition, PET / MR appears to be of paramount importance in prostate imaging as the latest tracer technologies (18F-ethylcholine, 68Ga-PSMA) not only provide high-specific imaging, but also the local MR imaging of the prostate is done at the same time (which had previously been carried out separately at a different time) as the PET examination. The patient can thus get a complete clarification within an appointment. This also applies to tumors in the gynecological area or carcinomas in the head and neck region.

The higher soft tissue contrast as well as the good reproducibility of edema (in the bone marrow) of the MRI compared to CT can be used as an advantage in numerous diseases. E.g. In the case of multiple myelomas, it is possible to combine the advantage of the MRI in the early detection of bone marrow lesions and the high recognition rate of the PET with respect to lesions outside of the bone.

A PET / MR can also be performed in patients with renal insufficiency, like PET / CT. However, as usual in the PET / CT, no contrast medium is normally given. However, in certain circumstances PET / MR has the possibility, even in cases of partial renal insufficiency, to give contrast agents, especially when there is an advantage to be expected in making the correct diagnosis.

PETMR.png
Figure 4

Top row: the overview (MIP = Maximum Intensity Projection) serves as a first general overview, here is shown an example of a neck / tongue tumor. The middle picture shows the CT of this neck / tongue. The image on the right shows the fused PET / CT. Bottom row: the left picture shows only the PET without CT or Top row: the overview (MIP = Maximum Intensity Projection) serves as a first general overview, here is shown an example of a neck / tongue tumor. The middle picture shows the CT of this neck / tongue. The image on the right shows the fused PET / CT. Bottom row: the left picture shows only the PET without CT or MR. The middle picture shows the MRI of the neck / tongue - the tumor (arrow) is clearly better defined. The image on the right shows the fused PET / MR

However, PET / MR does not only offer advantages over PET / CT, it is important to note that PET / CT is more suitable for some indications. The main disadvantage of the MRI at the moment is that especially in displaying the structures and diseases of the lung it is inferior to CT . However, research is carried out on corresponding sequences, which will hopefully provide the same qualitiy as CT in the future. In addition there are some contraindications for MR imaging like cardiac pacemakers, neurostimulator-devices or several implants.

If you have any questions, please do not hesitate to contact us at 044 255 1502. Since it is still a new method, the indications are constantly revised and expanded.

With regard to tracers we currently use:

18F-FDG e.g. For the following indications:
- Initial staging and recurrence diagnosis of various carcinomas (lung, throat and nasopharynx, pancreas, liver, ovary, esophageal gastrointestinal tract, etc.).
- Integrated brain MRI to exclude brain metastases
- Lymphoma diagnostics
- Advanced melanoma
- Tumors, with an unknown primary tumor
- Spinal Infection (for early detection within the first 2 weeks better than MRI)
- Unclear infection focus
- Dementia treatment
- Heart Examinations

18F-choline
- Primary staging and follow-up examination in prostate carcinoma
- highly sensitive and -specific parathyroid gland diagnostics

18F-FET
- brain tumor diagnosis, in particular differentiation of tumor tissue (residual / recurrent) of posttherapeutic changes

68Ga-PSMA
- highly sensitive and -specific diagnosis of prostate carcinoma

68Ga DOTATATE
- neuroendocrine tumors
- atypical meningiomas
- Paraganglioma diagnostics / search, if equivocal MIBG-SPECT

Patient information

PET/CT and PET/MR: