PET/CT > Post Test Answers


Post Test Answers


    1)  What is the cellular characteristic that most contributes to FDG accumulation in cancer cells?

    1. High mitotic rate
    2. Up regulation of glucose transporters and glycolytic enzymes
    3. Increased cell membrane permeability
    4. Over expression of high affinity cell surface receptors
    5. None of the above

     

    Answers:

    1. Incorrect. Increased mitotic rate may indirectly contribute to increased FDG uptake by increasing tumor volume; but, this is not the target for FDG molecular imaging.
    2. Correct. Hexokinase and glucose transporters (GLUT 1) are up regulated in tumor cells which have increased reliance on glycolysis for growth.
    3. Incorrect. FDG, a glucose analogue, enters cancer cells by facilitated transport, not passive diffusion; transmembrane glucose transporters are up regulated in malignant cells.
    4. Incorrect. FDG, a glucose analogue, enters cancer cells by facilitated transport of transmembrane glucose transporters, not cell surface receptors.
    5. Incorrect.


    Zhao S, Kuge Y, Mochizuki T, Takahashi T, Nakada K, Sato M, Takei T, Tamaki N. (2005) Biologic correlates of intratumoral heterogeneity in 18F-FDG distribution with regional expression of glucose transporters and hexokinase-II in experimental tumor. J Nucl Med. Apr;46(4):675-82.

    Brown RS, Leung JY, Kison PV, Zasadny KR, Flint A, Wahl RL. (1999) Glucose transporters and FDG uptake in untreated primary human non-small cell lung cancer. J Nucl Med. Apr;40(4):556-65.

    2)  While FDG PET targets neoplasms, increased uptake can also been seen in all the following processes except?

    1. Inflammation
    2. Infection
    3. Post radiation therapy
    4. Necrosis
    5. Surgical scar

     

    Answers:

    1. Incorrect. FDG uptake with inflammatory processes such as sarcoidosis can demonstrate activity equal to malignancy.
    2. Incorrect. FDG uptake with infectious processes such as bacterial, granulomatous or fungal disease of the lung can demonstrate activity equal to malignancy.
    3. Incorrect. Post radiation therapy injury to non target tissue can induce increased FDG uptake (e.g. heart, lung).
    4. Correct. Because FDG uptake requires viable cells to accumulate radiotracer, FDG does not accumulate in sites of necrosis.
    5. Incorrect. FDG uptake in post surgical inflammation and wound healing can mimic recurrent or residual disease although usually uptake is not as robust as with malignancy.


    Truong MT, Pan T, Erasmus JJ. Pitfalls in integrated CT-PET of the thorax: implications in oncologic imaging. J Thorac Imaging. 2006 May;21(2):111-22.


    3)  In comparing PET/CT to PET which on of the following is incorrect?

    1. CT attenuation correction is superior to positron transmission scan attenuation correction
    2. PET/CT improves anatomic localization of metabolic FDG activity
    3. A PET/CT scan requires more time than a PET-only scan
    4. PET/CT improves temporal correlation between PET and CT data

     

    Answers:

    1. Incorrect. CT attenuation correction reduces noise and scan time.
    2. Incorrect. The major strength of combined PET/CT is the precise anatomic localization of metabolic activity.
    3. Correct. A combined PET/CT scan takes less time than a PET-only scan because one obtains the attenuation scan with a CT scan faster than with positron transmission scan.
    4. Incorrect. By combining PET/CT in the same gantry improved temporal correlation is achieved between the modalities.


    Beyer T, Townsend DW. Putting 'clear' into nuclear medicine: a decade of PET/CT development. Eur J Nucl Med Mol Imaging. 2006 Aug;33(8):857-61.

    Kinahan PE, Hasegawa BH, Beyer T. X-ray-based attenuation correction for positron emission tomography/computed tomography scanners. Semin Nucl Med. 2003;33:166–179.

    Beyer T, Townsend DW, Brun T, Kinahan PE, Charron M, Roddy R, Jerin J, Young J, Byars L, Nutt R. A combined PET/CT scanner for clinical oncology. J Nucl Med. 2000 Aug;41(8):1369-79.


    4)  In regard to FDG PET imaging in 2007, the Center for Medicare and Medicaid Services provides reimbursement for all of the following indications except?

    1. Head and neck cancer (non-thyroid, non-CNS): diagnosis, staging, and restaging
    2. Brain tumor: diagnosis, staging, and restaging
    3. Myocardial viability: primary or initial diagnosis
    4. Refractory seizures (brain): pre-surgical evaluation
    5. Oncological indications not approved by CMS can be submitted through the National Oncologic PET Registration (NOPR) for Medicare reimbursement

     

    Answers:

    1. Incorrect. FDG PET is approved by CMS for head and neck cancer (non-thyroid, non-CNS): diagnosis, staging, and restaging.
    2. Correct. While FDG PET has proven valuable identifying brain tumors and in differentiating brain tumor from post therapy radiation changes, this indication is not approved by CME at this time. However, submission thought the National Oncological Pet Registry should cover this indication.
    3. Incorrect. FDG PET is approved by CMS for myocardial viability: primary or initial diagnosis or following an inconclusive SPECT prior to revascularization.
    4. Incorrect. FDG PET is approved by CMS for Refractory seizures (brain): pre-surgical evaluation only.
    5. Incorrect. The National Oncologic PET Registry (NOPR) is a collaborative registry in place to expand coverage for FDG PET to include cancers not presently eligible for Medicare reimbursement.


    Center for Medicare and Medicaid Services REF: http://www.cms.hhs.gov/Transmittals/downloads/R31NCD.pdf

    National Oncological Pet Registry REF: www.cancerpetregistry.org

    5)  Which one of the following statements is not true regarding PET attenuation artifacts?

    1. Non attenuation corrected PET data, attenuation corrected as well as co-registered PET CT data should all be viewed to improve interpretation and problem solve.
    2. Orthopedic prosthesis can generate “hot spots” in adjacent tissues on non attenuation corrected data.
    3. Non attenuation corrected data sets have low counts with in the central body structures like the spine.
    4. The lungs and skin appear darker on non attenuation corrected images compared to attenuation corrected data sets.
    5. PET attenuation artifacts occur with PET-CT and not PET-only.

     

    Answers:

    1. Incorrect. Non attenuation corrected PET data, attenuation corrected as well as co-registered PET CT data should all be viewed to improve interpretation and problem solve.
    2. Correct. Dense objects such as ports and metallic prosthesis will attenuate x-rays used for CT attenuation. When the PET data is reconstructed there is over correction for the focal attenuation and a “hot spot” is generated which can be mistaken for tumor. This artifact will not be present, or will be less obvious, on the non corrected PET data set.
    3. Incorrect. Non attenuation corrected data set are relatively photopenic centrally compared to peripherally. Although positrons emit high energy 511 keV particles attenuation, still occurs in body tissues.
    4. Incorrect. The lungs and skin appear darker on non attenuation corrected images compared to attenuation corrected data as there is minimal attenuation in these tissues.
    5. Incorrect. Attenuation correction artifacts can occur with PET-only, but are generally less severe.


    Beyer T, Townsend DW. Putting 'clear' into nuclear medicine: a decade of PET/CT development. Eur J Nucl Med Mol Imaging. 2006 Aug;33(8):857-61.


    6)  All of the following are true regarding Standard Uptake Values (SUVs) except

    1. SUVs are semiquantitative measurements based on FDG activity, administered dose, and body weight.
    2. SUVs above 2.5 are diagnostic of malignancy.
    3. SUVs can only be calculated on attenuation corrected images.
    4. SUVs may be calculated using body surface area instead of weight.

     

    Answers:

    1. Incorrect. A common formula for SUV calculation is:SUV=ROI activity (mCi/mL) / administered activity (mCi) / body weight (g)
    2. Correct. A SUV of 2.5 is suggestive of malignancy but not diagnostic. The 2.5 threshold was established from identifying malignancy with pulmonary nodules and should be used as a general guide. Other tumor types in different tissues may have higher or lower FDG avidity and SUVs. Additionally, there are many processes that demonstrate high metabolic activity (SUV > 2. 5) which are not malignant. (e.g. infection and inflammation).
    3. Incorrect. Accurate SUV activity ROIs can only be measured on the attenuation corrected data.
    4. Incorrect. SUV can be calculated substituting surface area for body weight in the following formula: SUV=ROI activity (mCi/mL) / administered activity (mCi) / body weight (g).


    Duhaylongsod FG, Lowe VJ, Patz EF Jr, Vaughn AL, Coleman RE, Wolfe WG. Detection of primary and recurrent lung cancer by means of F-18 fluorodeoxyglucose positron emission tomography (FDG PET). J Thorac Cardiovasc Surg 1995; 110:130-139; discussion 139-140.


    7)   Which of the following statements is false regarding FDG activity in the brain?

    1. FDG PET of the brain is clinically limited due to high background glucose metabolism.
    2. FDG PET of the brain can identify seizure foci.
    3. FDG PET of the brain can identify metabolism patterns associated with Alzheimer’s disease.
    4. FDG PET of the brain can identify brain tumors.

     

    Answers:

    1. Correct. While the brain utilizes glucose as the sole energy source resulting in high background activity, FDG PET is an important modality in neuroimaging. Several applications utilize hypometabolism patterns to identify pathology including epilepsy and Alzheimer’s disease while hypermetabolism can identify brain tumors.
    2. Incorrect. FDG PET brain scan can identify epileptogenic seizure foci with regions of FDG hypometabolism identified in the interictal phase.
    3. Incorrect. FDG PET scan can identify Alzheimer disease with patterns of hypometablism in the temporoparietal lobes.
    4. Incorrect. FDG PET can identify brain tumors against the background of high baseline glucose metabolism within normal brain tissue.


    Wong TZ, van der Westhuizen GJ, Coleman RE. Positron emission tomography imaging of brain tumors. Neuroimaging Clin N Am. 2002 Nov;12(4):615-26.

    Henry TR, Votaw JR The role of positron emission tomography with [18F]fluorodeoxyglucose in the evaluation of the epilepsies. Neuroimaging Clin N Am. 2004 Aug;14(3):517-35

    Coleman RE. Positron emission tomography diagnosis of Alzheimer's disease. Neuroimaging Clin N Am. 2005 Nov;15(4):837-46


    8)   Which of the following tissues would be expected to have the lowest background FDG activity?

    1. Liver
    2. Testicles
    3. Mediastinal lymph nodes
    4. Salivary glands
    5. Heart

     

    Answers:

    1. Incorrect. The liver is a major organ for carbohydrate metabolism and storage. Hepatocytes have accelerated uptake of cellular FDG compared to other organs. Consequently the liver has high background FDG activity often exceeding the blood pool.
    2. Incorrect. Normally, homogeneous low level activity is seen within the testicles.
    3. Correct. Normal lymph nodes demonstrate very little FDG activity.
    4. Incorrect. Normally, minimal or low level activity is seen in the submandibular, parotid, and sublingual salivary glands.
    5. Incorrect. With sufficient fasting (at least 6 hours) the myocardium theoretically shifts from glucose to fatty acid metabolism to fulfill its energy requirements and FDG myocardial activity should decrease to blood pool levels. However, in practice, variable and non-uniform myocardial activity is demonstrated even following an overnight fast.


    Wahl RL, Buchanan JW (editors): Principles and Practice of Positron Emission Tomography. Philadelphia, Lipppincott, Williams, & Wilkins, 2002.


    9)   Which of the following is true regarding FDG PET and endogenous glucose?

    1. In whole body scans, the patient fasts for 4 hours in part to reduce myocardium uptake.
    2. In whole body scans, the patient glucose loads to increase tumor uptake.
    3. Hyperglycemic states, found in diabetics, do not significantly alter FDG PET scans.
    4. Injection of insulin to hyperglycemic patients optimizes FDG PET scans.

     

    Answers:

    1. Correct. The heart preferentially utilizes lipids in the fasting state which lowers uptake of FDG.
    2. Incorrect. Glucose loading would raise serum glucose levels, and non-radioactive glucose would compete with FDG for tumor uptake. In contrast to body scans for oncology, glucose loading is used in dedicated cardiac FDG PET studies to promote cardiac uptake of FDG.
    3. Incorrect. Hyperglycemic states found in diabetics reduces uptake of FDG by tumor cells.
    4. Incorrect. Insulin injection prior to FDG PET scan translocates glucose transporters and results in increase muscle uptake in skeletal muscle and cardiac muscle, resulting in higher background and lower tumor conspicuity.


    Torizuka T, Zasadny KR, Wahl RL. Diabetes Decreases FDG Accumulation in Primary Lung Cancer. Clin Positron Imaging. 1999 Oct;2(5):281-287.

    Wahl RL, Buchanan JW (editors): Principles and Practice of Positron Emission Tomography. Philadelphia, Lipppincott, Williams, & Wilkins, 2002.


    10)   To avoid false negative FDG PET results, what is the target range for serum glucose?

    1. 0 - 50 mg/dl
    2. 50 - 100 mg/dl
    3. 100 - 150 mg/dl
    4. 150 - 200 mg/dl
    5. FDG PET results are not significantly affected by serum glucose level

     

    Answers:

    1. Incorrect. Hypoglycemic state harmful to patient.
    2. Incorrect. Hypoglycemic state is not necessary for FDG tumor imaging.
    3. Correct. Serum glucose up to 150 mg/dl should not significantly interfere with FDG uptake by target cells.
    4. Incorrect. At serum glucose levels above 150 mg/dl the clinician should consider rescheduling the patient with plans to bring glucose levels with in range. High levels of serum glucose can compete with tumor uptake of FDG and potentially lead to false negative results.
    5. Incorrect. FDG, a glucose analog, competes with endogenous glucose for transmembrane transport.


    11)   All of the following are potential artifacts which can mimic a malignancy on FDG PET-CT scan except?

    1. Metallic prosthesis
    2. Dense barium in bowel
    3. Chest ports
    4. Motion misregistration at the diaphragm
    5. FDG uptake in the larynx

     

    Answers:

    1. Incorrect. Metallic prosthesis such as artificial hips attenuate CT x-rays and the common reconstruction algorithm over corrects resulting in apparent focal high FDG activity in tissue adjacent to the prosthetic.
    2. Incorrect. Dense barium within bowel attenuates the CT beam and the common reconstruction algorithm over corrects placing high activity within the bowel.
    3. Incorrect. Chest ports attenuate the CT beam and the common reconstruction algorithm overcorrects placing a region of high FDG activity in the chest wall which may be mistaken for lung mass or lymph node.
    4. Incorrect. Motion misregistration at the diaphragm from breathing during the PET scan can place liver FDG activity in the right lower lobe which could be mistaken for a lung mass.
    5. Correct. While FDG uptake in the larynx (usually due to patient talking after injection of FDG) could be mistaken for neoplasm, this would be an interpretation error and not an artifact.



    12)   In regards to brown fat, which statement is true?

    1. Brown fat is adipose tissue with high glucose metabolism associated with heat generation.
    2. Brown fat activity can be reduced by premedicating with a benzodiazepine.
    3. Insuring adequate warmth for the patient before and during FDG PET scan can reduce brown fat activity.
    4. Brown fat can be confidently identified by characteristic locations.
    5. All of the above.

     

    Answers:

    1. Incorrect. Brown fat becomes activated as one of the initial steps in thermogenesis in response to cold. Through sympathetic innervations, glycolysis in brown fat is significantly increased. Higher levels of circulating catecholamines in anxious patients may also play a role in the stimulation of brown fat FDG uptake.
    2. Incorrect. Higher levels of circulating catecholamines in anxious patients may play a role in the stimulation of brown fat FDG metabolism. Premedicating with a benzodiazepine can reduce brown fat activity.
    3. Incorrect. Insuring adequate warmth in the patient before and during FDG PET scan can reduce brown fat activity.
    4. Incorrect . A pattern of multi-focal intense symmetric uptake along the neck, supraclavicular regions, mediastinum, and paraspinal regions can be seen, especially in children. The PET/CT fusion images localize this FDG uptake to areas of fat, rather than to any other soft tissues or masses.
    5. Correct. Brown fat consists of adipocytes which upregulate metabolism for thermoregulation. Brown fat has high FDG uptake consistent with the high metabolic rate. By keeping the patient warm and comfortable brown fat activity can be reduced. PET/CT confidently localizes brown fat to a typical pattern of multi-focal intense symmetric uptake along the neck, supraclavicular regions, mediastinum, and paraspinal regions can be seen.


    Cohade C, Osman M, Pannu HK, Wahl RL. Uptake in supraclavicular area fat ("USA-Fat"): description on 18F-FDG PET/CT. J Nucl Med. 2003 Feb;44(2):170-6.

    Hany TF, Gharehpapagh E, Kamel EM, Buck A, Himms-Hagen J, von Schulthess GK. Brown adipose tissue: a factor to consider in symmetrical tracer uptake in the neck and upper chest region. Eur J Nucl Med Mol Imaging. 2002 Oct;29(10):1393-8.


    13)   A breast cancer patient is undergoing a restaging FDG PET/CT 6 months after completion of neoadjuvant chemotherapy, radiotherapy and lumpectomy. New increased uptake is evident within several non adjacent vertebral bodies of the lumbar spine. Which of the following is the most likely explanation?

    1. Marrow response to chemotherapy
    2. Marrow response to granulocyte-colony stimulating factor (G-CSF)
    3. Marrow response to radiation therapy
    4. Tumor recurrence in vertebral bodies
    5. None of the above

     

    Answers:

    1. Incorrect. The cytotoxic effects of chemotherapy usually depress marrow elements and thus metabolic activity.
    2. Incorrect. G-CSF is administered in conjunction with chemotherapy to counteract chemotherapy-induced myelosuppression and can cause a flare in the marrow activity following treatment. This increased FDG uptake could be mistaken for recurrence, however the pattern in usually very uniform. The marrow flare response subsides by 1 month post treatment and is not likely the cause of increased marrow uptake activity 6 months out as in this case.
    3. Incorrect. Radiation therapy results in marrow toxicity with a pattern of well-demarcated difference from normal adjacent marrow, either decreased or increased in the radiation port, depending on the interval since radiation.
    4. Correct. Increased activity at scattered sites in the spine 6 months following completion of treatment is concerning for metastatic disease.
    5. Incorrect. Increased activity at scattered sites in the spine 6 months following completion of treatment is concerning for malignancy.


    Sugawara Y, Fisher SJ, Zasadny KR, Kison PV, Baker LH, Wahl RL. Preclinical and clinical studies of bone marrow uptake of fluorine-1-fluorodeoxyglucose with or without granulocyte colony-stimulating factor during chemotherapy. Cancer J Clin Oncol. 1998 Jan;16(1):173-80

    Kazama T, Swanston N, Podoloff DA, Macapinlac HA. Effect of colony-stimulating factor and conventional- or high-dose chemotherapy on FDG uptake in bone marrow Eur J Nucl Med Mol Imaging. 2005 Dec;32(12):1406-11.


    14)   Patient with papillary thyroid cancer status post total thyroidectomy and two previous I-131 therapies returns for followup which reveals with an elevated serum thyroglobulin level. I-131 diagnostic scan reveals no abnormal I-131 uptake. Which one of the following would be the most appropriate next step?

    1. FDG PET/CT scan
    2. I-131 ablation
    3. Contrast enhanced neck CT
    4. Contrast enhanced neck MRI
    5. Advise surgeon to re-operate on the neck

     

    Answers:

    1. Correct. Thyroid cancers which have dedifferentiated and no longer express the normal complement of I transporters frequently demonstrate increased FDG uptake due to increased metabolic activity.
    2. Incorrect. Additional therapy with I-131 is reasonable. A post therapy scan, obtained after a higher dose (100 mCi) than the diagnostic scan may reveal malignant tissue not evident at the lower diagnostic dose. However, a PET/CT scan prior to ablation may identify thyroid tumor which may be amenable to surgical resection.
    3. Incorrect. A contrast CT of the neck could potential demonstrate residual thyroid tissue or associated lymph node metastasis, however at PET/CT would be more sensitive and specific.
    4. Incorrect. A neck MRI would not have as high a resolution as a contrast CT or as specific as PET/CT.
    5. Incorrect. Without imaging guidance, repeat neck surgery would not be fruitful, and would be inappropriate if the recurrent tumor is outside the neck.


    Grunwald F.; Menzel C.; Bender H.; Palmedo H.; Willkomm P.; Ruhlmann J.; Franckson T.; Biersack H.-J. Comparison of 18FDG-PET with 131Iodine and 99mTc-sestamibi scintigraphy in differentiated thyroid cancer. Thyroid Volume 7(3), 1997, Pages 327-335.


    15)   A patient with history of sigmoid colon adenocarcinoma status post partial resection and chemotherapy receives a restaging PET/CT. There is a segment of high FDG activity within the lumen of the caecum. Which best characterizes the finding?

    1. Physiologic activity within stool
    2. Recurrent cancer
    3. Artifact from barium
    4. Colitis
    5. Indeterminate. Need additional clinical information or another study.

     

    Answers:

    1. Incorrect. Stool within the colon can retain FDG. The intraluminal activity would suggest stool; however, not definitive. Patient could repeat study after colon prep or receive colonoscopy.
    2. Incorrect. In a patient with previous colon cancer a high clinical suspicion for recurrence exist; however, false positives from stool, barium, colitis or normal colon are possibilities that need consideration. Close review of the CT data set, additional clinical history or additional study (e.g. colonoscopy) is warranted.
    3. Incorrect. Barium from a recent GI study can give false positive uptake on PET-CT. Barium can be identified on the CT data set and the artifact would not be present on the non attenuated corrected PET data set.
    4. Incorrect. Recruitment of inflammatory cells in colitis can result in increased FDG uptake in a segmental pattern in the bowel. Additional clinical history and laboratory data and review of CT data set should be able to rule in or out this diagnosis. An additional study (e.g. colonoscopy) may be warranted.
    5. Correct. Abnormal FDG uptake in the caecum in patient with history of colon cancer could be intraluminal stool, colitis, retained barium, or colon cancer. This case warrants careful review of the CT data set, non corrected PET data set, additional clinical data, and potentially an additional study (e.g. colonoscopy).


    Tatlidil R, Jadvar H, Bading JR, Conti PS Incidental colonic fluorodeoxyglucose uptake: correlation with colonoscopy and histopathology findings. Radiology 2002 224:783–787

    Rosenbaum SJ, Stergar H, Antoch G, Veit P, Bockisch A, Kuhl H. Staging and follow-up of gastrointestinal tumors with PET/CT. Abdom Imaging 2006. Jan-Feb;31(1):25-35.


    16)   Patient with fever and history of smoking has a LUL density on chest x-ray. CT thorax demonstrates a nodular focus of LUL air space disease and no mediastinal adenopathy. What is the best next course?

    1. PET/CT
    2. Repeat chest x-ray or CT thorax in one month after antibiotics
    3. Biopsy
    4. Wedge resection
    5. MRI

     

    Answers:

    1. Incorrect. PET/CT would not be warranted at this time in a patient without adenopathy and trial of antibiotics. The results would likely be equivocal, with uptake due either to an infectious or a malignant process.
    2. Correct. If the lesion is still present on chest x-ray or CT after adequate trial of antibiotics then PET/CT would be appropriate to assess the lung lesion. Of note, some fungal and granulomatous infections are PET positive and would be in the differential along with malignancy if the lung lesion demonstrated abnormal FDG uptake.
    3. Incorrect. Inappropriate at this stage.
    4. Incorrect. Inappropriate at this stage.
    5. Incorrect. MRI is not the best modality to assess lung parenchyma due to poor contrast in the lungs and breathing motion resulting in artifact.


    Truong MT, Pan T, Erasmus JJ. Pitfalls in integrated CT-PET of the thorax: implications in oncologic imaging. J Thorac Imaging. 2006 May;21(2):111-22