Thoracic positron emission tomography
- Paul Stark, MD
Paul Stark, MD
- Professor of Radiology
- University of California San Diego
Positron emission tomography (PET) allows in vivo imaging of metabolic, physiologic, and pathologic processes. It has been used as a research tool for many years, and has evolved into a clinically indispensable imaging examination. The increased clinical use is a consequence of regional commercial radiopharmacies being more able to supply hospitals throughout the country with radiopharmaceuticals, while the equipment has become more robust and financially more affordable. Traditional PET scanners with an array of several thousand ring detectors can be replaced by traditional two-headed single photon emission computed tomography (SPECT) gamma cameras that have been retrofitted with coincidence detectors to allow 18-fluoro-2-deoxyglucose (FDG)-PET imaging. Many PET scanners are being replaced by integrated whole-body PET and computed tomography scanners (PET/CT scanners) , while integrated, hybrid PET and magnetic resonance (PET/MR) scanners are being introduced as well [2,3].
Technical issues (ie, radionuclides, technique, sources of error) and the indications for thoracic PET imaging are reviewed here. The use of PET scanning in the evaluation of solitary pulmonary nodules or lung cancer staging is discussed separately. (See "Computed tomographic and positron emission tomographic scanning of pulmonary nodules" and "Imaging of non-small cell lung cancer".)
Radionuclides — Positron-emitting radionuclides are produced in a cyclotron (eg, oxygen-15, nitrogen-13, carbon-11, and fluorine-18) or by a generator (eg, rubidium-82, copper-62). Fluorine-18 is one such radionuclide that is produced by proton bombardment of oxygen-18 in a cyclotron. When it is bound to a D-glucose analog, it forms 18-fluoro-2-deoxyglucose (FDG), which is the most commonly used radionuclide in thoracic positron emission tomography (PET).
FDG is transported into cells where it is phosphorylated by hexokinase to form FDG-6-phosphate, which remains trapped temporarily because it is not further metabolized by the enzyme glucose-6-phosphatase, nor is it easily extruded from the cell. The fluorine-18 emits positrons as it decays, which travel a short distance before they are annihilated by electrons, resulting in the emission of two 0.511 MeV photons oriented at 180 degrees to each other. These events are registered when the photons collide with the sodium iodide or bismuth germanate contained within the scintillation detectors that surround the patient (image 1A-B), thereby triggering an electronic pulse within the scintillation crystal. Three-dimensional localization of the decay is possible because of the coincidence circuitry that detects the annihilation radiation . The end result is measurement of the distribution of FDG throughout the body. The FDG is eventually extruded from the cell, filtered by the glomerulus without being resorbed in the proximal convoluted tubule, and excreted in the urine.
Technique — During a PET scan, the patient lies within a scanner that consists of a moving table and gantry, reminiscent of the equipment used for computed tomography (CT). Before the administration of FDG, scans are obtained using a rotating germanium-68 pinpoint source. This process is called attenuation correction and its purpose is to adjust for the decrement of positron-related radiation caused by soft tissues of varying electron densities (figure 1) . FDG is injected intravenously using a dose of 10 to 20 mCi (370 to 740 MBq) and then multiple (ie, 30 to 45) axial (ie, cross-sectional) images are obtained. A cross-sectional, axial field of view of 16 to 20 cm and a spatial resolution of 5 mm are achieved at full width half maximum. Finally, axial, coronal, and sagittal projections are viewed on a workstation and whole body images can be generated.
- Blodgett TM, Meltzer CC, Townsend DW. PET/CT: form and function. Radiology 2007; 242:360.
- Schwenzer NF, Schraml C, Müller M, et al. Pulmonary lesion assessment: comparison of whole-body hybrid MR/PET and PET/CT imaging--pilot study. Radiology 2012; 264:551.
- Ohno Y, Koyama H, Yoshikawa T, et al. Three-way Comparison of Whole-Body MR, Coregistered Whole-Body FDG PET/MR, and Integrated Whole-Body FDG PET/CT Imaging: TNM and Stage Assessment Capability for Non-Small Cell Lung Cancer Patients. Radiology 2015; 275:849.
- DeGrado TR, Turkington TG, Williams JJ, et al. Performance characteristics of a whole-body PET scanner. J Nucl Med 1994; 35:1398.
- Lowe VJ, Naunheim KS. Positron emission tomography in lung cancer. Ann Thorac Surg 1998; 65:1821.
- Mettler FA Jr, Guiberteau MJ. Essentials of Nuclear Medicine Imaging, 5th ed, Saunders, Philadelphia 2005.
- O'Donnell JS, Rini J, Chusid J, Shah R. Abnormal Uptake on PET/CT: Imitators of Malignancy in Thoracic Imaging. Contemporary Diagnostic Radiology 2011; 34:1.
- von Schulthess GK, Steinert HC, Hany TF. Integrated PET/CT: current applications and future directions. Radiology 2006; 238:405.
- Gatenby RA, Gillies RJ. Why do cancers have high aerobic glycolysis? Nat Rev Cancer 2004; 4:891.
- Nolop KB, Rhodes CG, Brudin LH, et al. Glucose utilization in vivo by human pulmonary neoplasms. Cancer 1987; 60:2682.
- Wahl RL, Hutchins GD, Buchsbaum DJ, et al. 18F-2-deoxy-2-fluoro-D-glucose uptake into human tumor xenografts. Feasibility studies for cancer imaging with positron-emission tomography. Cancer 1991; 67:1544.
- Hatanaka M. Transport of sugars in tumor cell membranes. Biochim Biophys Acta 1974; 355:77.
- Langen KJ, Braun U, Rota Kops E, et al. The influence of plasma glucose levels on fluorine-18-fluorodeoxyglucose uptake in bronchial carcinomas. J Nucl Med 1993; 34:355.
- Chen HH, Chiu NT, Su WC, et al. Prognostic value of whole-body total lesion glycolysis at pretreatment FDG PET/CT in non-small cell lung cancer. Radiology 2012; 264:559.
- Gould MK, Maclean CC, Kuschner WG, et al. Accuracy of positron emission tomography for diagnosis of pulmonary nodules and mass lesions: a meta-analysis. JAMA 2001; 285:914.
- Roberts PF, Follette DM, von Haag D, et al. Factors associated with false-positive staging of lung cancer by positron emission tomography. Ann Thorac Surg 2000; 70:1154.
- Ulaner GA, Lyall A. Identifying and distinguishing treatment effects and complications from malignancy at FDG PET/CT. Radiographics 2013; 33:1817.
- Choi YW, Munden RF, Erasmus JJ, et al. Effects of radiation therapy on the lung: radiologic appearances and differential diagnosis. Radiographics 2004; 24:985.
- Asad S, Aquino SL, Piyavisetpat N, Fischman AJ. False-positive FDG positron emission tomography uptake in nonmalignant chest abnormalities. AJR Am J Roentgenol 2004; 182:983.
- Cypess AM, Lehman S, Williams G, et al. Identification and importance of brown adipose tissue in adult humans. N Engl J Med 2009; 360:1509.
- Virtanen KA, Lidell ME, Orava J, et al. Functional brown adipose tissue in healthy adults. N Engl J Med 2009; 360:1518.
- Cronin CG, Prakash P, Daniels GH, et al. Brown fat at PET/CT: correlation with patient characteristics. Radiology 2012; 263:836.
- Wang TJ. The natriuretic peptides and fat metabolism. N Engl J Med 2012; 367:377.
- Ferdinand B, Gupta P, Kramer EL. Spectrum of thymic uptake at 18F-FDG PET. Radiographics 2004; 24:1611.
- Erasmus JJ, McAdams HP, Patz EF Jr, et al. Evaluation of primary pulmonary carcinoid tumors using FDG PET. AJR Am J Roentgenol 1998; 170:1369.
- Higashi K, Ueda Y, Seki H, et al. Fluorine-18-FDG PET imaging is negative in bronchioloalveolar lung carcinoma. J Nucl Med 1998; 39:1016.
- Kim BT, Kim Y, Lee KS, et al. Localized form of bronchioloalveolar carcinoma: FDG PET findings. AJR Am J Roentgenol 1998; 170:935.
- Jadvar H, Segall GM. False-negative fluorine-18-FDG PET in metastatic carcinoid. J Nucl Med 1997; 38:1382.
- Nishino M, Hatabu H, Johnson BE, McLoud TC. State of the art: Response assessment in lung cancer in the era of genomic medicine. Radiology 2014; 271:6.
- Lowe VJ, Fletcher JW, Gobar L, et al. Prospective investigation of positron emission tomography in lung nodules. J Clin Oncol 1998; 16:1075.
- Torizuka T, Clavo AC, Wahl RL. Effect of hyperglycemia on in vitro tumor uptake of tritiated FDG, thymidine, L-methionine and L-leucine. J Nucl Med 1997; 38:382.
- Erasmus JJ, McAdams HP, Patz EF Jr, et al. Thoracic FDG PET: state of the art. Radiographics 1998; 18:5.
- Knight SB, Delbeke D, Stewart JR, Sandler MP. Evaluation of pulmonary lesions with FDG-PET. Comparison of findings in patients with and without a history of prior malignancy. Chest 1996; 109:982.
- Patz EF Jr, Goodman PC. Positron emission tomography imaging of the thorax. Radiol Clin North Am 1994; 32:811.
- Mac Manus MP, Hicks RJ, Ball DL, et al. F-18 fluorodeoxyglucose positron emission tomography staging in radical radiotherapy candidates with nonsmall cell lung carcinoma: powerful correlation with survival and high impact on treatment. Cancer 2001; 92:886.
- Mac Manus MP, Hicks RJ, Matthews JP, et al. Positron emission tomography is superior to computed tomography scanning for response-assessment after radical radiotherapy or chemoradiotherapy in patients with non-small-cell lung cancer. J Clin Oncol 2003; 21:1285.
- Bury T, Corhay JL, Duysinx B, et al. Value of FDG-PET in detecting residual or recurrent nonsmall cell lung cancer. Eur Respir J 1999; 14:1376.
- Keidar Z, Haim N, Guralnik L, et al. PET/CT using 18F-FDG in suspected lung cancer recurrence: diagnostic value and impact on patient management. J Nucl Med 2004; 45:1640.
- Bruzzi JF, Munden RF, Truong MT, et al. PET/CT of esophageal cancer: its role in clinical management. Radiographics 2007; 27:1635.
- Castillo R, Pham N, Castillo E, et al. Pre-Radiation Therapy Fluorine 18 Fluorodeoxyglucose PET Helps Identify Patients with Esophageal Cancer at High Risk for Radiation Pneumonitis. Radiology 2015; 275:822.
- Groheux D, Espié M, Giacchetti S, Hindié E. Performance of FDG PET/CT in the clinical management of breast cancer. Radiology 2013; 266:388.