This prospective study was conducted in a tertiary care center from 20 October 2018 to 15 December 2020. This study was approved by the committee of biomedical research ethics of our department.
Before including patients in the study, informed consent was obtained. The study aims, procedures, and risks were completely defined for the patients. It is essential to mention that this study had no interference with standard care for patients diagnosed with thyroid nodules
In this study, patients were already suspected or diagnosed with thyroid nodules by expert endocrinologists and referred to the radiology department for the thyroid nodule's ultrasound study. According to the American College of Radiology (ACR) Thyroid Imaging Reporting and Data System (TI-RADS), based on the size and structure of the nodules in ultrasound study, the TI-RADS score is indicative for either fallow-up or FNA of the nodule. In this study, we needed to determine the nature of the nodules by FNA and pathologic studies. Therefore, we only included (Fig. 1) patients with TI-RADS scores indicative of FNA, which is shown in Table1.
Indication of FNA considering TI-RADS score.
TI-RADS score indicative for FNA
1) score 3, size ≥ 2.5 cm
2) score 4 to 6, size ≥ 1.5 cm
3) score 7 or more, size ≥ 1 cm
The ultrasound study was performed by an expert radiologist with 10 years of experience in thyroid US using the same ultrasound scanner (siemens-healthineers, ACUSON NX) for all patients with a 15MHZ linear transducer. The examination was performed in transverse and longitudinal views to investigate any thyroid nodule, abnormal lymph node, tumor infiltration, metastasis, and other soft tissue pathologies differentially diagnosed thyroid nodule. The ultrasound study was reported according to the American College of radiologists' TIRAD system.
MRI was performed by a 1.5T scanner (Philips medical system, Ingenia ambition 1.5TX, the Netherlands) using a neck coil. All patients were studied by the same mentioned machine and coil.
The MRI protocol included Axial T2-weighted (T2WI) (repetition time/ echo time (TR/TE): 2904 ms/80 ms, slice thickness, 3 mm; gap, 0.5 mm; (number of excitation) NEX, 4; field of view (FOV), 16 cm; matrix,320 × 224) and DWI on axial plane on diffusion gradient b factor = 800 (TR/TE: 5000 ms/minimum; FOV, 16 cm; NEX, 4; matrix, 128 × 128; slice thickness, 4 mm; and gap = 0.5 mm.
Quantitative image analysis
Two radiologists with 10 and 8 years of experience in head and neck imaging who were blinded to the patients' ultrasound reports measured signal intensities of thyroid nodules and paraspinal muscles on T2-weighted imaging by placing a circular ROI cursor. In thyroid nodules, circular ROI covered the entire nodule at the largest cross-section area without including artifacts or cystic portions of the nodule. Signal intensity ratio(SIR) on T2-weighted was measured as a ratio of signal intensity of the thyroid nodule on T2-weighted to that of paraspinal muscle.
Also, signal intensities of background noise on T2-weighted were measured.
The Z value is calculated as following:
The DWI sequence was performed to obtain the ADC values of each patient's thyroid nodule by analyzing the ADC map for every individual (Fig. 2,3).
Ultrasound-guided FNA and cytology study
Under sterile conditions after ultrasound-guided localization of the nodule and local anesthesia, a 21-gauge or 22-gauge was used to perform aspiration biopsy. The specimen was fixed and stained for histopathology study. An expert interventional radiologist performed the FNA of the thyroid nodule for each patient in the intervention section of the AL-Zahra hospital's radiology department, Isfahan, Iran, and the samples were transported to the pathology department. The cytological study was performed independently by a pathologist, an expert in thyroid cytology. The pathologist was blinded to the patients' MRI and ultrasound results.
Quantitative variables were reported as mean, median, standard deviation, and interquartile ranges. Qualitative variables were reported as numbers and percentages. The quantitative data were assessed for being normal by the Kolmogorov-Smirnov test and Q-Q plot. The comparison of quantitative variables between the malignant and benign groups was made by two samples independent t-test. The diagnostic values of thyroid nodule signal intensity on T2-weighted, T2 SIR, Z value, ADC value of thyroid nodule, and the cut-off points of each parameter in the malignant and benign group were determined by analyzing the receiver operating characteristics (ROC). Sensitivity, specificity, positive likelihood ratio (LR+), and accuracy of the cut-off points were also determined. The area under the curve was reported with a 95% confidence interval.