Application of cellular microstructural diffusion MRI (cell size imaging) in rectal lesions: a preliminary study

Objectives: To explore the value of cellular microstructural mapping by IMPULSED (imaging microstructural parameters using limited spectrally edited diffusion) method in evaluating the histological type and prognostic factors of rectal lesions. Materials and methods: Sixty-six patients with rectal lesions were enrolled in this study. All subjects underwent MRI scans including conventional diffusion weighted imaging (DWI) and the IMPULSED MRI scans of oscillating gradient spin-echo (OGSE) and pulse gradient spin-echo (PGSE) sequences. Parameters including mean cell diameter (d(mean)), intracellular fraction (v(in)), extracellular diffusivity (d(ex)), cellularity, and apparent diffusion coefficient (ADC) values (ADC(PGSE), ADC(17Hz), ADC(33Hz), and ADC of conventional DWI) were measured in different histopathologic types, grades, stages, and structure invasion statuses. The receiver operating characteristic (ROC) curve analysis was used to evaluate diagnostic power. The sensitivity, specificity, and the corresponding area under the curves (AUCs) were calculated. Results: Our preliminary results illustrated that malignant lesion showed higher v(in) and cellularity ([0.2867 +/- 0.0697] vs. [0.1856 +/- 0.1011], [2.3508 +/- 0.6055] vs. [1.2716 +/- 0.4574], all P<0.05), lower d(ex) and ADC values (ADC(PGSE), ADC(17Hz), and ADC of conventional DWI) compared to benign lesion ([2.1637 +/- 0.3303 mu m(2)/ms] vs. [2.5595 +/- 0.5085 mu m(2)/ms], [0.9238 (0.7959, 1.0741) x10(-3) mm(2)/s] vs. [1.3373 +/- 0.3902x10(-3) mm(2)/s], [1.3204 +/- 0.2342x10(-3) mm(2)/s] vs. [1.8029 +/- 0.3119x10(-3) mm(2)/s], [0.7400 (0.6750, 0.8375) x10(-3) mm(2)/s] vs. [1.0550 +/- 1.1191x10(-3) mm(2)/s], all P<0.05), while no significant difference was seen for d(mean). V-in and cellularity of rectal common adenocarcinoma (AC) were significantly higher than those of rectal mucinous adenocarcinoma (MC) ([0.2994 +/- 0.0626] vs. [0.2028 +/- 0.0571], [2.4579 +/- 0.5553] vs. [1.6412 +/- 0.4347], all P<0.05), while dex and ADC values (ADC(PGSE), ADC(17Hz), ADC(33Hz), and ADC of conventional DWI) were lower in AC ([2.1189 +/- 0.3187 mu m(2)/ms] vs. [2.4609 +/- 0.2534 mu m(2)/ms], [0.8996 +/- 0.1583x10(-3) mm(2)/s] vs. [1.2072 +/- 0.2326x10(-3) mm(2)/s], [1.2714 +/- 0.1916x10(-3) mm(2)/s] vs. [1.6451 +/- 0.2420x10(-3) mm(2)/s], [1.8963 (1.6481, 2.1138) x10(-3) mm(2)/s] vs. [2.3104 +/- 0.3851x10(-3) mm(2)/s], [0.7341 +/- 0.8872x10(-3) mm(2)/s] vs. [1.1410 +/- 0.1840x10(-3) mm(2)/s], all P<0.05). In AC group, the d(mean) had significant difference between negative and positive tumor budding (TB) ([13.2590 +/- 1.3255 mu m] vs. [14.3014 +/- 1.1830 mu m], P<0.05). No significant difference of d(mean), v(in), d(ex), cellularity or ADC values was observed in AC with different grade, T stage, N stage, perineural and lymphovascular invasion (all P>0.05). The ROC curves showed that the area under the curves (AUCs) of v(in), d(ex), cellularity, and ADC values (ADC(PGSE), ADC(17Hz), and ADC of conventional DWI) for distinguishing malignant and benign lesion were 0.803, 0.757, 0.948, 0.807, 0.908 and 0.905, respectively. The AUCs of v(in), d(ex), cellularity, and ADC values (ADC(PGSE), ADC(17Hz), ADC(33Hz), and ADC of conventional DWI) in distinguishing AC from MC were 0.887, 0.802, 0.906, 0.896, 0.896, 0.781 and 0.991, respectively. The AUC of the d(mean) for evaluating TB status was 0.726. The AUC of ADC from conventional DWI for evaluating WHO grade was 0.739. Conclusion: Cellular microstructural mapping by the IMPULSED method has great potential in preoperative evaluation of rectal lesions. It could be helpful in differentiating malignant and benign lesions, distinguishing AC from MC, and in predicting the TB status.