2.3. DCE-MRI Imaging Sequence, Parameter Settings, and Scanning Scheme

In this study, all patients were examined on a Siemens superconductive MRI scanner using a combined head and neck coil. All images were calibrated, and the scanning parameters were consistent. The conventional sequence scanning parameters were as follows: T1 weighted imaging (T1WI) : TR: 108 ms, TE: 24 ms, FOV: 240 × 240 mm², matrix: 256 × 256, layer thickness: 5 mm, layer spacing: 2 mm, NEX 3; T2 weighted imaging (T2WI) : TR: 5090 ms, TE: 91 ms, FOV: 240 × 240 mm², matrix: 256 × 256, layer thickness: 5 mm, layer spacing: 2 mm, NEX 3; and T1 weighted imaging conventional enhanced (T1WI-CE) : TR: 108 ms, TE: 24 ms, FOV: 240 × 240 mm², matrix:256×256, layer thickness: 5 mm, layer spacing: 2 mm, NEX 3. DCE-MRI was scanned with a transverse section T1-twist sequence (TR: 6 ms, TE: 2.35 ms, layer thickness: 3.5 mm, layer spacing: 1.5 mm, FOV: 260 × 260 mm², matrix: 186 × 186, flip angle: 10°). The time resolution was 1.3 seconds for precollecting, and the arterial input function (AIF) was obtained. The contrast agent gadolinium diamine (gadolinium diamine is provided by GE Healthcare, Shanghai, China) was injected through the elbow vein at a speed of 4 ml/s and a total amount of 0.1 mmol/kg in the sixth period (a total of 70 periods), and immediately after, 20 ml of saline chaser was injected at the same rate. The total acquisition time was 6 minutes.

The scanning scheme was as follows: (1) the first scan was within 2 days after the operation and before the start of radiotherapy and chemotherapy, and this scan did not include a DCE-MRI scan; (2) the second scan was within 2 months after the operation after receiving simultaneous radiotherapy and chemotherapy, and this scan included a DCE-MRI scan; (3) after that, reexamination was carried out every three months, and the scan included a DCE-MRI scan; (4) each patient was reexamined at least three times, and the follow-up time was more than 6 months.