Simultaneous 18F-FDG-PET/MRI: Associations between diffusion, glucose metabolism and histopathological parameters in patients with head and neck squamous cell carcinoma
Introduction
Nowadays, magnetic resonance imaging (MRI) and 18F-fluorodesoxyglucose positron emission tomography/computed tomography (18F-FDG-PET/CT) are integrated in the work-up of head and neck cancer patients [1], [2], [3]. Regarding the use of PET/MRI in these patients there are discrepant findings reported in literature. Partovi et al. [1] reported that 18F-FDG-PET/MRI and 18F-FDG-PET/CT provide comparable results in the detection of primary tumor, lymph node and distant metastases. Other authors found similar results [2], [3]. However, Loffelbein et al. found that PET/MRI showed some advantages in comparison to PET/CT in the head and neck region [4]. They recently published a retrospective study comparing the diagnostic accuracy of retrospective PET–MRI fusion with MRI alone and 18F-FDG PET/CT. The authors suggested that for morphologic imaging multimodal PET/MRI is beneficial because of the superior soft tissue contrast and fewer artifacts from dental implants [4]. In addition, MRI allows functional imaging, such as the assessment of perfusion with dynamic contrast-enhanced MRI [4]. Furthermore, MRI can be completed by diffusion weighted imaging (DWI), which provides additional information regarding tumor texture [5], [6], [7]. For example in HNSCC, DWI correlated with cell density [7]. However, according to Queiroz et al. the use of DWI as part of PET/MRI to evaluate head and neck cancers does not provide diagnostically relevant information [8]. The authors also stated that the use of DWI might not be needed in clinical PET/MRI protocols for the staging or restaging of head and neck cancers [8].
Similarly, Grueneisen et al. reported that DWI in PET/MR imaging has no diagnostic benefit for whole-body staging of women with pelvic malignancies [9].
Varoquaux et al. [10] mentioned that HNSCC causes a decreased apparent diffusion coefficient (ADC) on DWI and an increased standardized uptake value (SUV) on 18F-FDG-PET/CT, so ADC and SUV may be used as independent biomarkers in HNSCC. Furthermore, a statistical not significant trend towards higher SUV and lower ADC was observed with increasing tumor dedifferentiation [10]. In addition, Nakajo et al. reported a significant inverse correlation of pretreatment primary tumor ADC and SUV with a similar potential to predict disease free survival of patients with HNSCC [11]. Baba et al. [12] investigated breast tumors and indicated that SUV and ADC were helpful parameters in differentiating benign from malignant breast tumors. The authors observed significant differences in ADC and SUV between benign and malignant breast tumors [12]. Moreover, a new parameter SUV/ADC was introduced by the authors [12]. Using SUV/ADC produced better results than SUV or ADC alone in differentiating benign from malignant tumors [12]. In addition, high SUV was found to correlate with larger tumor size, higher nuclear grade, and the triple-negative hormonal receptor profile [12]. High ADC was revealed to be correlated with negative progesterone receptor and positive human epidermal growth factor receptor 2 profiles [12].
These controversial findings regarding the role of glucose metabolism and DWI in tumor diagnosis and characterization may be related to the fact that both parameters may be associated with different tumor tissue features.
The purpose of this study was to analyze possible associations between functional parameters derived from simultaneous 18F-FDG-PET/MRI and histopathological parameters in patients with HNSCC.
Section snippets
Material and methods
This prospective study was approved by the institutional review board.
Results
For all tumors the mean SUVmax was 24.41 ± 6.51, the mean SUVmean was 15.01 ± 4.07 (Fig. 1, Fig. 2, Fig. 3).
Mean values of ADC parameters were as follows: ADCmin: 0.65 ± 0.20 × 10−3 mm2 s−1; ADCmean: 1.28 ± 0.18 × 10−3 mm2 s−1; and ADCmax: 2.16 ± 0.35 × 10−3 mm2 s−1 (Fig. 1, Fig. 2, Fig. 3). The mean values of the calculated combined parameters SUVmax/ADCmin and SUVmax/ADCmean were 41.57 ± 16.79 and 19.47 ± 6.23, respectively.
Histopathological analysis identified the following results: mean cell count was 1069.82 ±
Discussion
Our study identified several significant associations between SUV, ADC and histopathological parameters in HNSCC.
It is well known that malignant tumors have lower ADC values in comparison to benign lesions [5], [6]. For instance, Sasaki et al. showed in their study that sinonasal carcinomas had statistically significant lower ADC values in comparison to benign and inflammatory disorders [6]. Furthermore, some studies found that ADC-values were associated with several histological parameters,
Conflict of interest statement
The author O. Sabri received travel expenses from Siemens Healthcare related to lectures on PET/MRI, grants, travel expenses, speaker honoraria and payment for consultancy for Bayer Healthcare and Piramal Imaging. Apart from this all other authors declare no conflict of interest.
Acknowledgement
Funding of the combined PET/MRI system by the German Research Foundation (DFG – project SA669/9-1) is greatly acknowledged.
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