Korean J Radiol.  2015 Aug;16(4):919-928. 10.3348/kjr.2015.16.4.919.

Detection of Myocardial Metabolic Abnormalities by 18F-FDG PET/CT and Corresponding Pathological Changes in Beagles with Local Heart Irradiation

• Yan R
• Song J
• Wu Z
• Guo M
• Liu J
• Li J
• Hao X
• Li S

• KMID: 2155568
• DOI: http://doi.org/10.3348/kjr.2015.16.4.919

Abstract

OBJECTIVE
To determine the efficacy of 18F-fluorodeoxyglucose positron emission tomography/computed tomography (18F-FDG PET/CT) in the detection of radiation-induced myocardial damage in beagles by comparing two pre-scan preparation protocols as well as to determine the correlation between abnormal myocardial FDG uptake and pathological findings.
MATERIALS AND METHODS
The anterior myocardium of 12 beagles received radiotherapy locally with a single X-ray dose of 20 Gy. 18F-FDG cardiac PET/CT was performed at baseline and 3 months after radiation. Twelve beagles underwent two protocols before PET/CT: 12 hours of fasting (12H-F), 12H-F followed by a high-fat diet (F-HFD). Regions of interest were drawn on the irradiation and the non-irradiation fields to obtain their maximal standardized uptake values (SUVmax). Then the ratio of the SUV of the irradiation to the non-irradiation fields (INR) was computed. Histopathological changes were identified by light and electron microscopy.
RESULTS
Using the 12H-F protocol, the average INRs were 1.18 +/- 0.10 and 1.41 +/- 0.18 before and after irradiation, respectively (p = 0.021). Using the F-HFD protocol, the average INRs were 0.99 +/- 0.15 and 2.54 +/- 0.43, respectively (p < 0.001). High FDG uptake in irradiation field was detected in 33.3% (4/12) of 12H-F protocol and 83.3% (10/12) of F-HFD protocol in visual analysis, respectively (p = 0.031). The pathology of the irradiated myocardium showed obvious perivascular fibrosis and changes in mitochondrial vacuoles.
CONCLUSION
High FDG uptake in an irradiated field may be related with radiation-induced myocardial damage resulting from microvascular damage and mitochondrial injury. An F-HFD preparation protocol used before obtaining PET/CT can improve the sensitivity of the detection of cardiotoxicity associated with radiotherapy.

Keyword

18F-FDG PET/CT; Radiation-induced heart disease; Radiotherapy; Pathology

MeSH Terms

Animals
Dogs
Fasting
Fluorodeoxyglucose F18/*metabolism
Heart/*radiography
Heart Injuries/*radiography
Male
Myocardium/metabolism/pathology
Positron-Emission Tomography/*methods
Radiation Injuries/diagnosis/*radiography
Thoracic Neoplasms/radiotherapy
Tomography, X-Ray Computed/*methods
Fluorodeoxyglucose F18

Figure

• 

  Fig. 1 Description of two preparation protocols. 12H-F = 12 hours of fasting, FDG = fluorodeoxyglucose, F-HFD = fasting followed by a high-fat diet, HFD = high-fat diet, PET/CT = positron emission tomography/computed tomography

• 

  Fig. 2 18F-FDG cardiac PET/CT images before RT from beagles treated with two pre-scan preparations. Grade 0 image from M4 using F-HFD protocol shows homogeneously minimal myocardial FDG uptake; Grade 1 image from M3 using F-HFD protocol shows mostly minimal or mild myocardial FDG uptake; Grade 2 image from M10 using 12H-F protocol shows mostly intense or moderate myocardial FDG uptake; Grade 3 image from M2 using 12H-F protocol shows homogeneously intense myocardial FDG uptake. 12H-F = 12 hours of fasting, 18F-FDG = 18F-fluorodeoxyglucose, F-HFD = fasting followed by a high-fat diet, PET/CT = positron emission tomography/computed tomography, RT = radiotherapy

• 

  Fig. 3 Images of male beagle (M2) at baseline and 3 months after RT using F-HFD protocol. A. Dose-distribution axial image. B. Cardiac FDG-PET/CT axial images before RT. C. Cardiac FDG-PET/CT axial images 3 months after RT. D. Myovation images of FDG at 3 months after RT. B shows suppression of myocardial FDG uptake before RT. C and D show high FDG uptake (arrows) corresponding to irradiated field 3 months after RT. FDG = fluorodeoxyglucose, F-HFD = fasting followed by a high-fat diet, PET/CT = positron emission tomography/computed tomography, RT = radiotherapy

• 

  Fig. 4 Images of bealge (M2) 3 months after RT under 12H-F protocol. A. Cardiac FDG-PET/CT axial images 3 months after RT. B. Myovation images of FDG at 3 months after RT. No abnormal FDG uptake could be detected 3 months after RT. Physiological myocardial FDG uptake might interfere detecting pathological changes. 12H-F = 12 hours of fasting, FDG = fluorodeoxyglucose, PET/CT = positron emission tomography/computed tomography, RT = radiotherapy

• 

  Fig. 5 Hematoxylin and esoin staining of non-irradiated myocardium (A) and irradiated myocardium (B, C). Cytoplasmic vacuolization of myocytes (black arrows) (× 400) and perivascular fibrosis (green arrow) (× 200) were visible in irradiated field of myocardium.

• 

  Fig. 6 Electron transmission micrographs of myocardium. A. Abundant mitochondria packed around normal nuclei are shown in non-irradiated field (× 10000). B. Slightly dilated cristae in some mitochondria scattered around nucleus (black arrows), as well as enlarged nuclei (green arrows) were observed in irradiated myocardium (× 10000).

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