Purpose
To prospectively investigate the technical feasibility and performance of image fusion for whole-body diffusion-weighted imaging (wbDWI) and computed tomography (CT) to detect metastases using hybrid positron emission tomography/computed tomography (PET/CT) as reference standard.
Material and Methods
Fifty-two patients (60 ± 14 years; 18 women) with different malignant tumor disease examined by PET/CT for clinical reasons consented to undergo additional wbDWI at 1.5 Tesla. WbDWI was performed using a diffusion-weighted single-shot echo-planar imaging during free breathing. Images at b = 0 s/mm 2 and b = 700 s/mm 2 were acquired and apparent diffusion coefficient (ADC) maps were generated. Image fusion of wbDWI and CT (from PET/CT scan) was performed yielding for wbDWI/CT fused image data. One radiologist rated the success of image fusion and diagnostic image quality. The presence or absence of metastases on wbDWI/CT fused images was evaluated together with the separate wbDWI and CT images by two different, independent radiologists blinded to results from PET/CT. Detection rate and positive predictive values for diagnosing metastases was calculated. PET/CT examinations were used as reference standard.
Results
PET/CT identified 305 malignant lesions in 39 of 52 (75%) patients. WbDWI/CT image fusion was technically successful and yielded diagnostic image quality in 73% and 92% of patients, respectively. Interobserver agreement for the evaluation of wbDWI/CT images was κ = 0.78. WbDWI/CT identified 270 metastases in 43 of 52 (83%) patients. Overall detection rate and positive predictive value of wbDWI/CT was 89% (95% CI, 0.85–0.92) and 94% (95% CI, 0.92–0.97), respectively.
Conclusion
WbDWI/CT image fusion is technically feasible in a clinical setting and allows the diagnostic assessment of metastatic tumor disease detecting nine of 10 lesions as compared with PET/CT.
Whole-body (wb) positron emission tomography (PET) is playing an important role in staging of cancer providing functional information on tumor metabolism. The main limitation of PET is the poor spatial resolution, which has been overcome with the introduction of dual-modality PET/computed tomography (CT) imaging . The combination of metabolic and anatomical image data as dual-modality scanners have markedly increased lesion localization and diagnostic accuracy compared to both modalities as standalone applications .
Malignant lesions are not only characterized by pathologic metabolism (eg, high glucose uptake), which is used for 18F-2-fluoro-2-deoxy-D-glucose (18F-FDG)-PET imaging, but also by higher cellularity consistent with restriction of water diffusion. Diffusion-weighted imaging (DWI) allows the measurement of water diffusion on a molecular level and is able to depict malignant lesions as areas of impeded diffusion. DWI has a great potential for tumor imaging and its value in various malignancies has been reported in several studies . Similar to PET imaging, DWI lacks sufficient anatomical information, due to low signal of physiologic anatomic structures. Therefore the capability of wbDWI is usually investigated together with magnetic resonance imaging (MRI) providing anatomical information. However, it is not evident yet, if the molecular information derived from wbDWI may potentially replace PET when evaluated under the same prerequisites namely CT imaging.
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Material and methods
Patients
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PET/CT
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wbDWI
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Image Post Processing
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Image Analysis
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PET/CT
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wbDWI/CT: image quality
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wbDWI/CT: detection of malignancy
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Statistical Analysis
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Results
Patients
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PET/CT
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Table 1
Lesion-based Detection Rates and Positive Predictive Values for Detecting Metastases by wbDWI/CT Image Fusion, wbDWI, and CT Images using PET/CT as the Reference
Organs Number of Metastases Detection Rate PPV PET/CT wbDWI/CT wbDWI/CT(%) TP FP FN (%) (%) Liver 75 71 5 4 95 (0.89–1.00) 93 (0.87–0.99) Lung 69 66 1 3 96 (0.90–1.00) 99 (0.95–1.00) Lymph nodes 122 104 6 18 85 (0.79–0.92) 95 (0.90–0.99) Pancreas 2 2 0 0 100 (0.75–1.00) 100 (0.83–1.00) Intestinal tract 5 4 0 1 80 (0.35–1.00) 100 (0.88–1.00) Urogenital system 6 2 2 4 33 (0–0.79) 50 (0–1.00) Spleen 2 0 0 2 0 0 Soft tissue 11 11 1 0 100 (0.95–1.00) 92 (0.72–1.00) Skeletal system 9 6 1 3 67 (0.30–1.00) 86 (0.53–1.00) Central nervous system 4 4 0 0 100 (0.88–1.00) 100 (0.88–1.00) Total 305 270 16 35 89 (0.85–0.92) 94 (0.92–0.97)
FN, false negative; FP, false positive; PET/CT, positron emission tomography/computed tomography; PPV, positive predictive value; TP, true positive; wbDWI/CT, whole-body diffusion-weighted imaging/CT.
Numbers in parentheses are 95% confidence intervals.
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Image Quality
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Table 2
Image Quality Analyses of Fused wbDWI/CT Images
Fusion Quality of wbDWI/CT Diagnostic Image Quality of wbDWI/CT as compared to PET/CT Poor image fusion in 14 /52 (26.9) Worse and of nondiagnostic quality in 4/52 (7.7) Satisfactory image fusion in 34/52 (65.4) Worse but of diagnostic quality in 41/52 (78.8) Correct image fusion in 4/52 (7.7) Equal quality in 7/52 (13.5)
wbDWI, whole-body diffusion-weighted imaging.
Numbers in parentheses are percentages.
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wbDWI/CT: Detection of malignancy
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Discussion
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Image Quality
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Detection of Malignancy
Liver, lung, and lymph nodes
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Intestinal tract, soft tissue, skeletal system, and central nervous system
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Pancreas, spleen, and urogenital system
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Limitations
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Conclusion
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