Editorial for “Longitudinal Multiparametric Magnetic Resonance Imaging Assessment of Irradiated Salivary Gland in a Rat Model: Correlated with Histological Findings”

Editorial for “Longitudinal Multiparametric Magnetic Resonance Imaging Assessment of Irradiated Salivary Gland in a Rat Model: Correlated with Histological Findings” Xerostomia is one of the most frequent adverse events following irradiation in patients with head and neck carcinoma, which results from histological damage of the salivary glands and requires preventive and curative intervention both during and after their therapeutic course in long-term survivors. Although magnetic resonance imaging (MRI) is a noninvasive modality that can quantitatively reveal changes in histology, fibrosis, and perfusion in irradiated parotid glands, corresponding histological validation remains limited because of difficulties in harvesting sufficient histological samples to allow comprehensive investigations using experimental animal models by Chen et al. In the article by Chen et al in this issue of JMRI, they advanced our understanding of the relationship between submandibular gland pathology of experimental Sprague–Dawley rat with a single dose of 15 Gy irradiation and multiparametric MRI using 3T-MRI. They carefully performed histopathological and radiological analyses and made comparisons between acinar cell fraction (AC%), microvessel density (MVD), degree of fibrosis (F%), and MRI parameters of T1 value, T2 value, apparent diffusion coefficient (ADC), f, D*, and D maps. Spearman’s rank correlation analysis showed a strong negative correlation between ADC, D, and AC% (P < 0.001). Moreover, they observed a moderate negative correlation between T2 value and AC% (P = 0.004), a moderate positive correlation between f and MVD (P = 0.022), and a moderate negative correlation between D* and MVD (P = 0.001). In addition, T1 value had a strong positive correlation with F% (P < 0.001). ADC is one of the most discussed parameters for several organs, which includes the salivary gland when it is damaged in various situations, such as irradiation (as in the present article), chronic inflammation, or atrophy by secretion inhibition. Marzi et al reported that significant ADC changes occur between preand postradiation therapy and discussed that ADC and D are dependent on the characteristics of glandular tissue. The data by Chen et al provide a comprehensive answer on the relationship between diffusion parameters and irradiated salivary glands. This is of considerable value to the readers of JMRI, and offers consensus of MRI findings in patients with irradiated submandibular glands. Although the article by Chen et al is a prospective study, there are several limitations. One limitation is that they performed a single irradiation exposure to the salivary gland, despite the fact that patients who receive irradiation in the head and neck undergo fractionated irradiation. We appreciate that it is challenging to perform fractionated irradiation in rats; however, we anticipate that more clinically oriented experiment protocols will be conducted in the future. Another limitation is that the study by Chen et al used an irradiation dose of up to 15 Gy, even though patients who undergo irradiation for head and neck lesion carcinoma receive up to 23 Gy for the contralateral parotid gland by reducing irradiation dose and applying intensity modulated radiotherapy (IMRT). Furthermore, Tasaka et al reported that xerostomia after irradiation in patients with nasopharyngeal carcinoma who received IMRT of the parotid gland received a mean dose of less than 40 Gy. The irradiated dose in this article was considerably smaller than that used in clinical settings. However, a single 15-Gy irradiation to the salivary gland of experimental Sprague–Dawley rats resulted in multiple deaths; thus, this is likely the reason that Chen et al used such a dose. The article by Chen et al in this issue of JMRI extends the characteristic findings of salivary glands using 3T-MRI without contrast enhancement and irradiated salivary glands. They provide a step toward the applicability of the methods to clinical settings for patients who undergo irradiation of the salivary gland.