Arterial spin labeling and diffusion-weighted imaging for identification of retropharyngeal lymph nodes in patients with nasopharyngeal carcinoma

Abstract

Background: To evaluate the parameters derived from arterial spin labeling (ASL) and multi-b-value diffusion-weighted imaging (DWI) for differentiating retropharyngeal lymph nodes (RLNs) in patients with nasopharyngeal carcinoma (NPC).

Methods: This prospective study included 50 newly diagnosed NPC and 23 healthy control (HC) participants. RLNs of NPC were diagnosed according to the follow-up MRI after radiotherapy. Parameters derived from ASL and multi-b-value DWI, and RLNs axial size on pre-treatment MRI among groups were compared. Receiver operating characteristic curve (ROC) was used to analyze the diagnostic efficiency.

Results: A total of 133 RLNs were collected and divided into a metastatic group (n = 71) and two non-metastatic groups (n = 62, including 29 nodes from NPC and 33 nodes from HC). The axial size, blood flow (BF), and apparent diffusion coefficient (ADC) of RLNs were significantly different between the metastasis and the non-metastasis group. For NPC patients with a short axis < 5 mm or < 6 mm, or long axis < 7 mm, if BF > 54 mL/min/100 g or ADC ≤ 0.95 × 10^-3 mm²/s, the RLNs were still considered metastatic. Compared with the index alone, a combination of size and functional parameters could improve the accuracy significantly, except the long axis combined with ADC; especially, combined size with BF exhibited better performance with an accuracy of 91.00-92.00%.

Conclusions: ASL and multi-b-value DWI could help determine the N stage of NPC, while the BF combination with RLNs size may significantly improve the diagnostic efficiency.

Keywords: Diffusion magnetic resonance imaging; Magnetic resonance imaging; Nasopharyngeal neoplasms; Perfusion imaging.

Fig. 1

Box-plots of comparisons between three groups. Error bar plots showed the difference of short axis (a), long axis (b), mean BF (c), and ADC (d) values of RLNs with LNM (metastatic RLNs from NPC patients), non-LNM1 (non-metastatic RLNs from NPC patients), and non-LNM2 (non-metastatic RLNs from healthy control participants)

Fig. 2

ROC by size, BF, and ADC to differentiate metastatic RLNs

Fig. 3

F29, NPC with bilateral metastatic RLNs. Axial T2WI before treatment (a) showed an irregular mass with heterogeneous slightly high signal intensity in the left lateral portion of the nasopharyngeal cavity and bilateral RLNs (curved arrows) with the size as long axis × short axis of 7 × 5 mm (right) and 8 × 5 mm (left), respectively. The primary tumor and RLNs demonstrated higher perfusion compared with the surrounding tissue on the fused image obtained by ASL and T2WI (b), and the map of BF (c). ROI of the RLNs were delineated on the map of BF (c) and multi-b-value DWI with b value at 800 s/mm² (d), acquiring at BF value of 60.63 mL/100 g/min, 67.71 mL/100 g/min, and ADC value of 0.808 × 10⁻³ mm²/s, 0.812 × 10⁻³ mm²/s on ADC map (e), respectively. Axial T2WI at three months after radiotherapy (f) showed the lymph nodes (stright arrows) were significantly reduced with the size of 4 × 2 mm (right) and 3 × 2 mm (left), respectively. Meanwhile, the tumor in the nasopharynx has complete regression

Fig. 4

M50, NPC with right metastatic RLN, and left non-metastatic RLN. Axial T2WI before treatment (a) showed bilateral RLNs with slightly high heterogeneous signal intensity and size as long axis × short axis of 19 × 11 mm (right, curved arrow) and 7 × 5 mm (left, straight arrow), respectively. Both lymph nodes demonstrated higher perfusion than the surrounding tissue on the fused image by T2WI and ASL (b), and the map of BF (c), especially the right one with remarkable pseudo-color contrast. On the fused image (b), the high perfusion area behind the right lymph node (arrowhead) was the internal carotid. ROI of the lymph nodes were delineated on the map of BF (c) and multi-b-value DWI with b value = 800 s/mm² (d), acquiring at BF value of 89.64 mL/100 g/min, 49.50 mL/100 g/min, and ADC value of 0.715 × 10⁻³ mm²/s, 0.893 × 10⁻³ mm²/s on ADC map (e), respectively. Axial T2WI at three months after radiotherapy (f) showed the size was remarkably reduced to 6 × 3 mm on the right lymph node (curved arrow) and was reduced (but not significantly) to 7 × 4 mm on the left lymph node (straight arrow)

Fig. 5

F28, healthy control with bilateral non-metastatic RLNs. Axial T2WI (a) shows bilateral RLNs (curved arrows) with heterogeneous slightly high signal intensity and size as long axis × short axis of 5 × 4 mm (right) and 7 × 5 mm (left), respectively. Both lymph nodes showed slightly higher perfusion compared with the surrounding tissue on the fused image by ASL and T2WI (b), with a BF value of 42.5 mL/100 g/min and 32.14 mL/100 g/min. ROI of the lymph nodes was delineated on the multi-b-value DWI with b value = 800 s/mm² (c), acquiring at ADC value of 0.993 × 10⁻³ mm²/s and 0.874 × 10⁻³ mm²/s on ADC map (d), respectively