PET- CT imaging (Positron Emission Tomography - Computerized Tomography) : A brief overview

PET- CT imaging (Positron Emission Tomography -

Computerized Tomography) : A brief overview

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Technology Update

PET- CT imaging (Positron Emission Tomography -Computerized Tomography) : A brief overview

Mythri Shankar a,*, Jyotsna Rao b

a Senior Consultant, Apollo Hospitals e Bangalore, Indiab Senior Consultant, Apollo Hospitals e Hyderabad, India

a r t i c l e i n f o

Article history:

Received 12 August 2014

Accepted 29 October 2014

Available online xxx

Keywords:

PET (positron emission tomography)

F18 FDG (Fluoro Deoxy Glucose)

SUV

* Corresponding author.E-mail address: dr.mythrishankar@gmail

Please cite this article in press as: Shanmography) : A brief overview, Apollo Me

http://dx.doi.org/10.1016/j.apme.2014.10.0030976-0016/Copyright © 2014, Indraprastha M

a b s t r a c t

PET (positron emission tomography) is functional imaging performed tagging short lived

radio isotopes produced in a cyclotron with organic molecules. The CT component of the

scanner helps with attenuation correction improving image quality. The CT images help in

precisely localizing lesions and clarifying confounding normal physiologic and anatomic

variants. It is important to differentiate between normal physiologic uptake and abnormal

or variable metabolic activity and identify artifacts. False positives in oncological imaging

occur in trauma, infection and inflammation. The primary indications for FDG PET CT in

Oncology are Diagnosis of malignancy and unknown primary, Staging of cancers, Restag-

ing, Monitoring response to therapy, Radiation therapy planning, and Guiding biopsy of

masses. There has been substantial evidence in the medical literature where PET CT has

brought about a change in the course of the management and in several cases reduced the

economic and financial burden of the disease.

Copyright © 2014, Indraprastha Medical Corporation Ltd. All rights reserved.

1. What is it

PET (positron emission tomography) is functional imaging

performed tagging short lived radio isotopes produced in a

cyclotron with organic molecules. The most commonly used

radiotracer in clinical practice is F18 FDG which fluorine 18

tagged with Fluoro Deoxy Glucose. Pic 1: PETCT Scanner.

2. How is it done

The basic principle involved in it FDG PET imaging is that

glucose transport and utilization is increased significantly in

malignancy, inflammation and infection at the cellular level.

.com (M. Shankar).

kar M, Rao J, PET- CT imdicine (2014), http://dx.d

edical Corporation Ltd. A

The F18 emits high-energy photons, which are detected by

crystal in the PET scanners. The FDG accumulation shows

areas of high metabolism. The CT component of the scanner

helps with attenuation correction improving image quality.

The CT images help in precisely localizing lesions and clari-

fying confounding normal physiologic and anatomic variants.

The amount of FDG accumulation in the lesion can be

measured in reference to other like liver and a Standardized

Uptake Value (SUV) can be quantified. The SUV serves as a

relative reference and aids in the diagnosis more in favor

of malignancy, monitor patient's treatment response and

delineate tumor volumes in PETCT-RT. SUV ¼ Mean region of

interest activity (mCi/mL) ¼ administered activity (mCi)/body

weight (g) expressed in g/mL.Radiation from a PET

aging (Positron Emission Tomography - Computerized To-oi.org/10.1016/j.apme.2014.10.003

ll rights reserved.

mailto:[email protected]

www.sciencedirect.com/science/journal/09760016

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http://dx.doi.org/10.1016/j.apme.2014.10.003



Fig. 1 e Scanner.


CT ¼ 20e25 mSv(approximately twice that from an coronary

angiogram). Patients need to be fasting for four hours prior to

FDG intravenous injection to prevent competitive inhibition of

glucose uptake in cells. Following a waiting period of one hour

after injection scanning starts with CT which takes a few

seconds followed by PET imaging which is done from base of

skull to mid thigh for 20 min in oncology patients keeping in

view low sensitivity of FDG PET for brain metastases and low

probability of metastases to lower limbs. Head to toe imaging

is performed in certain conditions like malignant melanoma,

sarcomas and cutaneous lymphomas. Pic 2: Pancreatic Cancer

with Liver Mets.

Fig. 2 e Pancreatic Cancer with Liver mets.

Please cite this article in press as: Shankar M, Rao J, PET- CT immography) : A brief overview, Apollo Medicine (2014), http://dx.d

3. Where it can be confusing

It is important to differentiate between normal physiologic

uptakeandabnormal or variablemetabolic activity and identify

artifacts. Falsepositives inoncological imagingoccur in trauma,

infection and inflammation. False negatives occur in slow

growing and low grade tumors, signet ring, mucinous tumor,

bronchoalveolar carcinoma, lowgradeprostatecarcinoma,well

differentiated HCC, differentiated neuroendocrine tumors,

cholangiocarcinomas, ampulary carcinomas, miliary carcino-

matosis. Tumor necrosis and sclerotic bonemetastases. And in

cases of Hyperglycemia and/or insulin given 3 h prior to FDG.

4. Which indications best suited?

The primary indications for FDG PET CT in Oncology are

Diagnosis of malignancy and unknown primary, Staging of

cancers, Restaging, Monitoring response to therapy, Radiation

therapy planning, and Guiding biopsy of masses. Cardiac PET

in useful assessment of perfusion and myocardial viability

and Brain PET in diagnosis the of Alzheimer's disease. Table 1

Most Common Indications OF PETCT & Fig. 3: Treatment

Response e Stable Diesase.1

5. Why is it needed?

There has been substantial evidence in the medical literature

where PET CT has brought about a change in the course of the

management and in several cases reduced the economic and

financial burden of the disease.2 Following are citied examples

in each category:

5.1. Head/neck cancer

Detectingprimary tumor site (occult) inpatientspresentingwith

metastatic disease, Initial staging and restaging after treatment

to detect residual disease. Sensitivity for head and neck cancers

Table 1 e Most common indications of PETCT.

Oncology

- Diagnosis

- Staging

- Restaging

- Evaluate Recurrence

- Assessment of Treatment response

- RT planning

Cardiology- Perfusion

- Viability

Neurology- Diagnosis of Alzheimer's- Seizure Localization

Infection:- Localization of infections focus

- FUO

- Diagnosis of an Infectious process e TB, Sarcoidosis.




Fig. 3 e Treatment Response e Stable disease.

Fig. 4 e Malignant Plueral Efflusion.

a p o l l o m e d i c i n e x x x ( 2 0 1 4 ) 1e4 3

is very high. Proven to be useful in patients treated who have

been treated with surgery and radiation distorting anatomy.

5.2. Thyroid cancer

Detecting residual or recurrent thyroid cancer when serum

thyroglobulin (Tg) is high and I131 * scan is negative. Staging in

poorly differentiated thyroid cancers and invasive Hurtle cell

carcinomas, assess treatment response. It has a low sensi-

tivity for well differentiated thyroid cancer.3,4

5.3. Breast cancer

Initial staging& Follow-upwhen conventional studies (e.g., CT

Scan or bone scan) are equivocal or suspicious.

5.4. Lung cancer

Characterization of an indeterminate pulmonary nodule

(>8e10 mm), Initial staging in NSCLC & SCLC, gross-tumor

volume estimation in patients receiving radiation therapy. It

is part of standardmanagement protocol with NSCLC and has

low sensitivity for bronchoalveolar carcinoma.5

5.5. Esophageal cancer

Initial staging (assess resectability), Restaging after neo-

adjuvant chemotherapy (CT) and/or radiation (RT), CT

response assessment, RT gross-tumor volume estimation.

5.6. Colorecal cancer

Preoperative resectability, localize tumors in high CEA level,

evaluate recurrence.


5.7. Cervical cancer

Initial treatment planning assistance, including determina-

tion of extra pelvic/systemic spread, Detection of residual or

recurrent disease following initial treatment which may be

potentially resectable/curable, Suggested for use in radiation

treatment planning (to help define nodal volume of coverage)

5.8. Melanoma

Detection and localization of potential extra nodal metastatic

lesions in initial evaluation of patients with advanced stage

disease, Evaluation of the extent of metastatic disease burden

in patients with recurrent disease following treatment, Post-

treatment screening for recurrent/metastatic disease in pa-

tients with advanced stage disease. High sensitivity in

restaging and monitoring response to therapy in malignant

melanoma.6

5.9. Lymphoma

Routine pre-treatment staging of patients with HD and

many NHL subtypes, Routine restaging/assessment of

treatment response after chemotherapy and/or radiation

therapy.7

In gynecological cancers, high sensitivity for cervical,

endometrial, vaginal and vulval cancers. In ovarian cancer,

useful for restaging and may help avoid second look laparot-

omy. Low sensitivity with mucinous ovarian cancers.

Useful in almost all Gastro intestinal tumors with excep-

tions mentioned above.

Useful in management of penile cancers. Indicated in

restaging and monitoring response to therapy in testicular

cancer. Higher sensitivity in soft tissue metastases in

aggressive poorly differentiated and hormone resistant pros-

tate carcinoma with high Gleason score and PSA. Pic 4: Ma-

lignant Pleural Effusion.





When to order: Timing is important.

While Monitoring Response:

Surgical Site: 2 months for surgical site, anytime anywhere

else.

Radiation Therapy: FDG uptake after 6 months of comple-

tion of radiation indicates tumor recurrence.

Early after RT within 2 months can represent radiation

changes.

Therefore wait for as long as possible after radiation before

planning PETCT. Comparison with baseline& radiation port is

helpful.

Chemotherapy: for 2e4 weeks: BM & spleen due to regen-

erating hyperplasia: worse if BM stimulating actors have been

administered with chemo (G-CSF, nuepogen), possibility of

transient stunning and inflammatory response (metabolic

flare) should also be considered.

Wait for atleast 2 weeks after last chemo or just before next

cycle, 2 months after completion of therapy.

Fig. 6 e Brain Images.

6. Cardiac PET e perfusion & viability

Apart from identifying, cardiac ischemia with N13 ammonia

(half life 10 min) and myocardial viability with FDG, PET has

been used to in the diagnosis of myocarditis due to causes

such as sarcoidosis and tuberculosis. A high fat meal is given

to the patient to suppress normal myocardial uptake so that

any uptake seen on the cardiac scan would be due to

myocardial inflammation. Pic 5: Cardiac PET - Short Axis.

7. Brain PET

FDG PET can confirm the clinical diagnosis of dementias such

as Alzheimer's disease. It is also useful in the presurgical

evaluation of medically refractory temporal lobe epilepsy. Pic

6: Brain PET.

Sodium Fluoride Bone Scans show higher sensitivity than

Tc 99m MDP in identifying skeletal lesions. Vascular flow and

immediate blood pooling cannot be performed. Scans show

high sensitivity in identifying facet joint arthritis and

Fig. 5 e Cardiac Short Axis.


vertebral end plate changes in patients with back ache and

failed back syndrome.

Ga68 DOTANOC useful in the diagnosis, staging, restaging,

monitoring response to therapy and radiation planning of

patients with tumors expressing somatostatin receptors

which include neuroendocrine cancers, pheochromocytoma,

medullary cancers and meningiomas. Ga68 is produced in a

generator unlike fluorine 18.

Ga68 PSMA can is a tracer which can help in management

of aggressive prostate cancer which express prostate specific

membrane antigen (PSMA).

Conflicts of interest

All authors have none to declare.

r e f e r e n c e s

1. Recommendations on the use of 18F-FDG PET in oncology.J Nucl Med. 2008 Mar;49(3):480e508.

2. NCCN Clinical Practice Guidelines in Oncology TM. vol. 1. 2013.3. Guidelines taskforce on thyroid nodules and differentiated

thyroid cancer. Thyroid. 2009;19(11):1167e1214.4. Thyroid Carcinoma Task Force. AACE/AAES medical/surgical

guidelines for clinical practice: management of thyroidcarcinoma. Endocr Pract. 2001;7(3):202e220.

5. Alberts WM. Clinical practice Guidelines (2nd Edition)executive summary: ACCP evidence-based diagnosis andmanagement of lung cancer. Chest. 2007;132:1e19.

6. Evidence-based Clinical Practice Guideline: Treatment of CutaneousMelanoma. American Society of Plastic Surgeons; 2007.

7. Subcommittee of International Harmonization Project inlymphoma. J Clin Oncol. 2007;25:571e578.


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PET- CT imaging (Positron Emission Tomography - Computerized Tomography) : A brief overview