Nononcological Applications of Positron Emission Tomography for Evaluation of the Thorax

A prospective study of the feasibility of FDG-PET/CT imaging to quantify radiation-induced lung inflammation in locally advanced non-small cell lung cancer patients receiving proton or photon radiotherapy

PURPOSE

This prospective study assessed the feasibility of ¹⁸F-2-fluoro-2-deoxy-D-glucose (FDG) positron emission tomography/computed tomography (PET/CT) to quantify radiation-induced lung inflammation in patients with locally advanced non-small cell lung cancer (NSCLC) who received radiotherapy (RT), and compared the differences in inflammation in the ipsilateral and contralateral lungs following proton and photon RT.

METHODS

Thirty-nine consecutive patients with NSCLC underwent FDG-PET/CT imaging before and after RT on a prospective study. A novel quantitative approach utilized regions of interest placed around the anatomical boundaries of the lung parenchyma and provided lung mean standardized uptake value (SUVmean), global lung glycolysis (GLG), global lung parenchymal glycolysis (GLPG) and total lung volume (LV). To quantify primary tumor metabolic response to RT, an adaptive contrast-oriented thresholding algorithm was applied to measure metabolically active tumor volume (MTV), tumor uncorrected SUVmean, tumor partial volume corrected SUVmean (tumor-PVC-SUVmean), and total lesion glycolysis (TLG). Parameters of FDG-PET/CT scans before and after RT were compared using two-tailed paired t-tests.

RESULTS

All tumor parameters after either proton or photon RT decreased significantly (p < 0.001). Among the 21 patients treated exclusively with proton RT, no significant increase in PVC-SUVmean or PVC-GLPG was observed in ipsilateral lungs after the PVC parameters of primary tumor were subtracted (p = 0.114 and p = 0.453, respectively). Also, there were no significant increases in SUVmean or GLG of contralateral lungs of patients who received proton RT (p = 0.841, p = 0.241, respectively). In contrast, among the nine patients who received photon RT, there was a statistically significant increase in PVC-GLPG of ipsilateral lung (p < 0.001) and in GLG of contralateral (p = 0.036) lung. In the subset of nine patients who received a combined proton and photon RT, there was a statistically significant increase in PVC-GLPG of ipsilateral lung (p < 0.001).

CONCLUSION

Our data suggest less induction of inflammatory response in both the ipsilateral and contralateral lungs of patients treated with proton compared to photon or combined proton-photon RT.

What, where and why: exploring fluorodeoxyglucose-PET's ability to localise and differentiate infection from cancer

PURPOSE OF REVIEW

To review the utility of FDG-PET imaging in detecting the cause of fever and infection in patients with cancer.

RECENT FINDINGS

FDG-PET has been shown to have high sensitivity and accuracy for causes of neutropenic fever, leading to higher diagnostic certainty in this group. Recent advances in pathogen-specific labelling in PET to identify Aspergillus spp. and Yersinia spp. infections in mice, as well as differentiating between Gram-positive, Gram-negative and mycobacterial infections are promising.

SUMMARY

Patients with cancer are vulnerable to infection and fever, and the causes of these are frequently unclear using conventional diagnostic methods leading to high morbidity and mortality, length of stay and costs of care. FDG-PET/CT, with its unique complementary functional and anatomical information as well as its whole-body imaging capability, has demonstrated use in detecting occult infection in immunocompromised patients, including invasive fungal and occult bacterial infections, as well as defining extent of infection. By demonstrating disease resolution following treatment and allowing earlier cessation of therapy, FDG-PET acts as a key tool for antimicrobial and antifungal stewardship. Limitations include at times poor differentiation between infection, malignancy and sterile inflammation, however, exciting new technologies specific to infectious pathogens may help alleviate that issue. Further prospective randomised research is needed to explore these benefits in a nonbiased fashion.

A Study of the Feasibility of FDG-PET/CT to Systematically Detect and Quantify Differential Metabolic Effects of Chronic Tobacco Use in Organs of the Whole Body-A Prospective Pilot Study

RATIONALE AND OBJECTIVES

The aim of this study was to assess the feasibility of ¹⁸F-fluorodeoxyglucose (FDG)-positron emission tomography/computed tomography (PET/CT) to systematically detect and quantify differential effects of chronic tobacco use in organs of the whole body.

MATERIALS AND METHODS

Twenty healthy male subjects (10 nonsmokers and 10 chronic heavy smokers) were enrolled. Subjects underwent whole-body FDG-PET/CT, diagnostic unenhanced chest CT, mini-mental state examination, urine testing for oxidative stress, and serum testing. The organs of interest (thyroid, skin, skeletal muscle, aorta, heart, lung, adipose tissue, liver, spleen, brain, lumbar spinal bone marrow, and testis) were analyzed on FDG-PET/CT images to determine their metabolic activities using standardized uptake value (SUV) or metabolic volumetric product (MVP). Measurements were compared between subject groups using two-sample t tests or Wilcoxon rank-sum tests as determined by tests for normality. Correlational analyses were also performed.

RESULTS

FDG-PET/CT revealed significantly decreased metabolic activity of lumbar spinal bone marrow (MVPmean: 29.8 ± 9.7 cc vs 40.8 ± 11.6 cc, P = 0.03) and liver (SUVmean: 1.8 ± 0.2 vs 2.0 ± 0.2, P = 0.049) and increased metabolic activity of visceral adipose tissue (SUVmean: 0.35 ± 0.10 vs 0.26 ± 0.06, P = 0.02) in chronic smokers compared to nonsmokers. Normalized visceral adipose tissue volume was also significantly decreased (P = 0.04) in chronic smokers. There were no statistically significant differences in the metabolic activity of other assessed organs.

CONCLUSIONS

Subclinical organ effects of chronic tobacco use are detectable and quantifiable on FDG-PET/CT. FDG-PET/CT may, therefore, play a major role in the study of systemic toxic effects of tobacco use in organs of the whole body for clinical or research purposes.

Automatic anatomy recognition in whole-body PET/CT images

PURPOSE

Whole-body positron emission tomography/computed tomography (PET/CT) has become a standard method of imaging patients with various disease conditions, especially cancer. Body-wide accurate quantification of disease burden in PET/CT images is important for characterizing lesions, staging disease, prognosticating patient outcome, planning treatment, and evaluating disease response to therapeutic interventions. However, body-wide anatomy recognition in PET/CT is a critical first step for accurately and automatically quantifying disease body-wide, body-region-wise, and organwise. This latter process, however, has remained a challenge due to the lower quality of the anatomic information portrayed in the CT component of this imaging modality and the paucity of anatomic details in the PET component. In this paper, the authors demonstrate the adaptation of a recently developed automatic anatomy recognition (AAR) methodology [Udupa et al., "Body-wide hierarchical fuzzy modeling, recognition, and delineation of anatomy in medical images," Med. Image Anal. 18, 752-771 (2014)] to PET/CT images. Their goal was to test what level of object localization accuracy can be achieved on PET/CT compared to that achieved on diagnostic CT images.

METHODS

The authors advance the AAR approach in this work in three fronts: (i) from body-region-wise treatment in the work of Udupa et al. to whole body; (ii) from the use of image intensity in optimal object recognition in the work of Udupa et al. to intensity plus object-specific texture properties, and (iii) from the intramodality model-building-recognition strategy to the intermodality approach. The whole-body approach allows consideration of relationships among objects in different body regions, which was previously not possible. Consideration of object texture allows generalizing the previous optimal threshold-based fuzzy model recognition method from intensity images to any derived fuzzy membership image, and in the process, to bring performance to the level achieved on diagnostic CT and MR images in body-region-wise approaches. The intermodality approach fosters the use of already existing fuzzy models, previously created from diagnostic CT images, on PET/CT and other derived images, thus truly separating the modality-independent object assembly anatomy from modality-specific tissue property portrayal in the image.

RESULTS

Key ways of combining the above three basic ideas lead them to 15 different strategies for recognizing objects in PET/CT images. Utilizing 50 diagnostic CT image data sets from the thoracic and abdominal body regions and 16 whole-body PET/CT image data sets, the authors compare the recognition performance among these 15 strategies on 18 objects from the thorax, abdomen, and pelvis in object localization error and size estimation error. Particularly on texture membership images, object localization is within three voxels on whole-body low-dose CT images and 2 voxels on body-region-wise low-dose images of known true locations. Surprisingly, even on direct body-region-wise PET images, localization error within 3 voxels seems possible.

CONCLUSIONS

The previous body-region-wise approach can be extended to whole-body torso with similar object localization performance. Combined use of image texture and intensity property yields the best object localization accuracy. In both body-region-wise and whole-body approaches, recognition performance on low-dose CT images reaches levels previously achieved on diagnostic CT images. The best object recognition strategy varies among objects; the proposed framework however allows employing a strategy that is optimal for each object.

Solitary lung masses due to occult aspiration

BACKGROUND

Aspiration occurs commonly, at times clinically occult, and is recognized to cause a widening spectrum of lung disorders. Presentation of aspiration as a lung mass has not been described.

METHODS

Among cases of aspiration-related pulmonary diseases diagnosed at Mayo Clinic (Rochester, Minn) from 2007 to 2013, 3 patients were identified to have presented with a solitary lung mass lesion.

RESULTS

The age of 3 patients, all men with a history of gastroesophageal reflux disease, ranged from 53 to 65 years. All patients presented with dyspnea, cough, and intermittent fevers. Chest computed tomography in each patient demonstrated malignant-appearing solitary lung mass, cavitated in 2 patients. Two patients underwent positron emission tomography, which showed intense fluorodeoxyglucose uptake in the lung mass for both. Surgical lung resection revealed acute and organizing pneumonia with giant cell reaction to foreign material, consistent with aspiration in all 3 patients. None of these lung masses were located in the "dependent" (posterior or basal) lung zones. These patients were managed with antireflux medical therapy; 1 patient underwent a Nissen fundoplication procedure for recurrent symptoms. No additional aspiration-related complications occurred during the follow-up period ranging from 24 to 84 months.

CONCLUSIONS

Aspiration-related pulmonary complications can present as a solitary lung mass that may not be located in dependent lung zones, which have traditionally been associated with aspiration-related pulmonary diseases.

FDG PET imaging in sarcoidosis

The objective of this review is to highlight the clinical utility of FDG-PET/CT for evaluation of patients with chronic sarcoidosis. The emphasis was on the potential advantages and disadvantages of this technique in these patients based on which recommendations were made. The advantage of FDG-PET/CT technique is that it can visualize FDG accumulation in activated inflammatory cells and simultaneously provide PET and CT images. Of particular interest is the use of FDG-PET/CT for the staging and identification of occult sites and sites suitable for biopsy and for the assessment of inflammatory active sarcoidosis in patients with prolonged symptoms, especially when other markers of the disease are within normal values. FDG-PET/CT also provides a better visualization of extrathoracic sites of active sarcoidosis, such as in the bones, liver, spleen, and retroperitoneal lymph nodes. The use of FDG-PET/CT is of special interest in cardiac sarcoidosis because this potentially life-threatening disease is sometimes present in asymptomatic patients. FDG-PET/CT also has a role in the clinical management of patients with chronic persistent sarcoidosis, such as for planning treatment, monitoring response, and long-term follow-up. The limitations of FDG-PET/CT in patients with sarcoidosis are discussed in the context of a "sarcoidosis-lymphoma syndrome" and potentially excessive radiation exposure. Further prospective multicentre studies are needed to refine the clinical applications of FDG-PET/CT in patients with sarcoidosis and drive the field forward.

The pivotal role of FDG-PET/CT in modern medicine

The technology behind positron emission tomography (PET) and the most widely used tracer, 2-deoxy-2-[18F]fluoro-D-glucose (FDG), were both conceived in the 1970s, but the latest decade has witnessed a rapid emergence of FDG-PET as an effective imaging technique. This is not least due to the emergence of hybrid scanners combining PET with computed tomography (PET/CT). Molecular imaging has enormous potential for advancing biological research and patient care, and FDG-PET/CT is currently the most widely used technology in this domain. In this review, we discuss contemporary applications of FDG-PET and FDG-PET/CT as well as novel developments in quantification and potential future indications including the emerging new modality PET/magnetic resonance imaging.

Quantitative assessment of global lung inflammation following radiation therapy using FDG PET/CT: a pilot study

PURPOSE

Radiation pneumonitis is the most severe dose-limiting complication in patients receiving thoracic radiation therapy. The aim of this study was to quantify global lung inflammation following radiation therapy using FDG PET/CT.

METHODS

We studied 20 subjects with stage III non-small-cell lung carcinoma who had undergone FDG PET/CT imaging before and after radiation therapy. On all PET/CT studies, the sectional lung volume (sLV) of each lung was calculated from each slice by multiplying the lung area by slice thickness. The sectional lung glycolysis (sLG) was calculated by multiplying the sLV and the lung sectional mean standardized uptake value (sSUVmean) on each slice passing through the lung. The lung volume (LV) was calculated by adding all sLVs from the lung, and the global lung glycolysis (GLG) was calculated by adding all sLGs from the lung. Finally, the lung SUVmean was calculated by dividing the GLG by the LV. The amount of inflammation in the lung parenchyma directly receiving radiation therapy was calculated by subtracting tumor measurements from GLG.

RESULTS

In the lung directly receiving radiation therapy, the lung parenchyma SUVmean and global lung parenchymal glycolysis were significantly increased following therapy. In the contralateral lung (internal control), no significant changes were observed in lung SUVmean or GLG following radiation therapy.

CONCLUSION

Global lung parenchymal glycolysis and lung parenchymal SUVmean may serve as potentially useful biomarkers to quantify lung inflammation on FDG PET/CT following thoracic radiation therapy.