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 Table of Contents  
ORIGINAL ARTICLE
Year : 2017  |  Volume : 13  |  Issue : 5  |  Page : 748-755

Optimization of b-values in diffusion-weighted imaging for esophageal cancer: Measuring the longitudinal length of gross tumor volume and evaluating chemoradiotherapeutic efficacy


1 Department of Radiology, The 1st Affiliated Hospital of PLA General Hospital, Beijing, China
2 Department of Radiology, The 95th Hospital of PLA, Putian, China
3 Department of Radiology, Chinese PLA General Hospital, Beijing, China

Date of Web Publication13-Dec-2017

Correspondence Address:
Tianran Li
Department of Radiology, The 1st Affiliated Hospital of PLA General Hospital, No. 51 Fucheng Road, Haidian, Beijing 100048
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/jcrt.JCRT_630_17

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 > Abstract 


Purpose: To study the optimization of b-values of magnetic resonance-diffusion-weighted (MR-DWI) in evaluating the chemoradiotherapeutic efficacy for esophageal squamous cell carcinoma (ESCC) and measuring the longitudinal length of gross tumor volume (GTV) of ESCC.
Materials and Methods: Eighteen patients with biopsy-proven ESCC were undergoing concurrent chemoradiotherapy (CCRT). Conventional magnetic resonance imaging (MRI) combined with DWI using b-values of 600 s/mm2, 800 s/mm2, and 1000 s/mm2 was performed before CCRT and after the 1st, 3rd, 5th, and 10th weeks. The apparent diffusion coefficient (ADC) values of ESCC were derived from DWI using multiple b-values. The correlations between ADC values and apoptosis positive rates of ESCC cells obtained from the endoscope biopsy were statistically analyzed. Thirty-eight patients with confirmed ESCC who underwent radical surgery were analyzed. Longitudinal length of GTV of ESCC was measured using endoscopy, esophageal barium fluoroscopy, computed tomography (CT), and T2-weighted MRI and DWI using different b-values (b = 400, 600, and 800 s/mm2) before surgery and were compared with pathologic lesion length.
Results: The ADC values of DWI images with different b-values are positively correlated with ESCC cell apoptosis positive ratios, the relation is significant, especially in the group of b = 1000 s/mm2 (P < 0.01). The measured length of esophageal lesions from short to long was MR-DWI b = 800 s/mm2, endoscopy, real tumor, MR-DWI b = 600 s/mm2, esophageal barium fluoroscopy, CT, and MR-DWI b = 400 s/mm2.
Conclusion: MR-DWI b = 800 s/mm2 and b = 1000 s/mm2 are in favor of observing the chemoradiotherapeutic efficacy with time variation and evaluating the chemoradiotherapeutic efficacy, respectively. MR-DWI b = 600 s/mm2 could be used as a supplementary means in measuring the length of ESCC.

Keywords: Apparent diffusion coefficient, diffusion-weighted imaging, esophageal squamous cell carcinoma, gross tumor volume, magnetic resonance imaging


How to cite this article:
Liu G, Yang Z, Li T, Yang L, Zheng X, Cai L. Optimization of b-values in diffusion-weighted imaging for esophageal cancer: Measuring the longitudinal length of gross tumor volume and evaluating chemoradiotherapeutic efficacy. J Can Res Ther 2017;13:748-55

How to cite this URL:
Liu G, Yang Z, Li T, Yang L, Zheng X, Cai L. Optimization of b-values in diffusion-weighted imaging for esophageal cancer: Measuring the longitudinal length of gross tumor volume and evaluating chemoradiotherapeutic efficacy. J Can Res Ther [serial online] 2017 [cited 2019 Nov 17];13:748-55. Available from: http://www.cancerjournal.net/text.asp?2017/13/5/748/220480




 > Introduction Top


Esophageal carcinoma (EC) ranks number eighth among the most common malignant tumor and leads to sixth highest number of cancer-related deaths worldwide. Among the total cases, more than 80% are reported in developing countries.[1],[2] It is also one of the most common cancers and a leading cause of death in China.[3] With majority of the cases being diagnosed at advanced stages, only about 20% of the cases are resectable, therefore leading to the lowest 5-year survival rate (10%) among the cancers.[1] While adenocarcinoma is more prevalent in the Caucasians, >90% of Chinese patients with EC develop esophageal squamous cell carcinoma (ESCC).[3]

At present, concurrent chemoradiotherapy (CCRT) is considered as the standard treatment for nonresectable ESCC, followed by evaluation of therapeutic response to treatment using computed tomography (CT), endoscopic ultrasound, and esophagography imaging.[4] Use of18 fluorine-fludeoxyglucose (18 F-FDG) to determine therapeutic response is limited due to its higher cost.[5] With the development in magnetic resonance imaging (MRI)-diffusion-weighted imaging (DWI), evaluation of CCRT response of tumors has improved.[6] CCRT lowers the cell membrane integrity, which results in an increase of the apparent diffusion coefficient (ADC) of water molecules of ESCC.[7],[8]

With studies showing high rates of achievement of therapeutic response along with high sensitivity and accuracy in ESCC patients, use of DWI-MRI might grow as a methodology to determine the therapeutic response to ESCC.[9],[10]

Therefore, early diagnosis of the tumor and evaluation of therapeutic response after CCRT using MRI-DWI with optimized b-values may support in providing evidence for clinical decision-making. This study was, therefore, performed to investigate the correlation between the change of ADC and pathology of ESCC at the beginning and after CCRT. The study further explored the predictive ability of different b-values in MRI-DWI to measure the length of ESCC.


 > Materials and Methods Top


Study design and patient selection

This was a single-center, prospective analysis performed in adult patients (aged ≥18 years) who underwent CCRT for ESCC from March 2010 to December 2014 at our center. For the CCRT response analysis group to determine the efficacy of CCRT in ESCC, the patients were included in the study if they had: (i) undergone upper endoscopic examination along with tumor biopsy; ii) had a confirmed diagnosis of ESCC; (iii) not received prior chemotherapy, radiotherapy, or surgical treatment; and (iv) were willing to undergo CCRT. For the gross tumor volume (GTV) assessment group to determine the longitudinal length of GTV, patients who had undergone radical surgery during the study period were included.

All patients were histopathologically diagnosed with ESCC before surgery by upper endoscopic and tumor biopsy. Lengths of lesions were measured in all patients by applicated endoscopy, esophageal barium fluoroscopy, CT scans, and MR-DWI. Transthoracic esophagostomy operations were performed within 1–3 days after the above-mentioned examinations.

The study protocol was approved by the Institutional Ethics Committee of the 1st Affiliated Hospital of PLA General Hospital, in accordance with the International Conference on Harmonization guidelines for Good Clinical Practice (ICH-GCP E6, 1996), Declaration of Helsinki (1964) and its subsequent revisions. All patients received information on the purpose and conduct of this study and provided written informed consent.

Magnetic resonance imaging scanning methods

All patients were trained for breath-holding technique before MRI to reproduce achieve precision in inspiration for each scan series. MRI was performed using a 3.0 T clinical- and scientific-type scanner (Siemens Verio, 32 channels) with routine transverse scan and patients positioned supine on the scanning bed. The peripheral pulse-gated two-dimensional (2D)-FLASH/T1WI transverse scan was set at the following parameters: TR/TE = 129 ms/2.46 ms, FA 70°, field of view (FOV) 285 mm × 380 mm, matrix 256 × 256, NEX 1, section thickness 5 mm; gap 5 mm, scan time 47 s. 2D-TSE/T2-weighted (T2WI) transverse scan: TR/TE = 1800 ms/TE 94 ms, FA 160°, FOV 360 mm × 270 mm, matrix 256 × 256, NEX 1, section thickness 5 mm, gap 1 mm; scan time 68 s. DWI was acquired using a single-shot echo-planar imaging sequence with the array spatial sensitivity encoding technique in the transverse plane during breathholding with a set parameters of TR/TE = TR 2000 ms/TE 73 ms, FOV 380 mm × 285 mm, matrix 128 × 128, NEX 2, section thickness 5 mm, gap 0 mm, and scan time 349 s.

MRI-DWI examination method of the CCRT response analysis group included DWI of b = 0.600, 800, and 1000 s/mm2 and was performed before and at the 1st, 3rd, 5th, and 10th weeks after CCRT. Navigator-triggered and pulse-gating techniques were used simultaneously during the scanning.

B-values of 0, 400, 600, and 800 s/mm2 and T2WI images were used for the GTV assessment group to define high-intensity regions. The average lesion lengths were calculated according to the amount slices with tumor on axial images. The images were evaluated by an independent, blinded reviewer.

Equipment and dosing

We used the radiotherapy linear accelerator VarianClinac 21E, USA; GTV of ESCC measured with 95% isodose curve and total dose of 60 Gy/30 fractions/6 weeks. All the patients of the CCRT response analysis group received CCRT of neoadjuvant chemotherapy (Nedaplatin 40 mg, 1/week).

Study outcomes

A RECIST criterion (version 1.1) was used as the response evaluation criteria of the CCRT response analysis group.[11] The outcomes included: (i) complete response (CR, defined as disappearance of all target lesions, with no new lesion and normal tumor marker for at least 4 weeks); (ii) partial response (PR, defined as ≥30% decrease in the sum of diameters of target lesions for at least 4 weeks); (iii) stable disease (SD, defined as neither sufficient shrinkage to qualify for PR nor sufficient increase to qualify for PD, taking as reference the smallest sum diameters while on study; and (iv) progressive disease (PD, defined as ≥20% increase in the sum of diameters of target lesions).

Apoptosis detection

Posttreatment biopsies for apoptosis analysis were performed within 1–3 days after MRI-DWI examination. The blood vessels were removed from the tumor sample. 1 mg/ml collagenase was added every 5 min at 37°C to the tissue sample to aid digestion of cellular membrane. After 30 min, 1 ml medium was added to terminate the digestion. A 200-mesh screen was used to filter the sample followed by centrifugation at 1500 rpm for 5 min. The sample was washed twice with 1 ml phosphate-buffered saline adding suitable amount of propidium iodide and Annexin-V, and flow cytometry count was performed, adjusting cells count to 106/ml.

Esophageal squamous cell carcinoma length and gross tumor volume evaluation

The patients of the GTV assessment group were made to fast for 6 h before the esophageal barium fluoroscopy and endoscopy. Lesion length was photographed from different positions and average length was calculated from three calculations.

For GTV determination, plain and enhanced CT were used via a spiral CT scanner (Brilliance iCT, Philips Medical, Best/Heeren, The Netherlands) and layer thickness of 0.625 mm, interlayer spacing of 3 mm, and FOV of 36–38 mm. Approximately 100 ml nonionic contrast media (Ioversol 350 mgI/100 ml) was used for enhanced CT scan. The scan included the chest entrance of the suprasternal fossa to the lower edge of the liver. CT images were transferred to treatment planning systems through local area network, and esophageal GTVs were delineated based on CT images. All CT images were reviewed by the same two experienced radiologists. Thickening of the esophageal wall >5 mm or the esophageal diameter >10 mm without gas in it or local or circumferential thickening of esophageal wall and/or associated with local luminal stenosis were included in the GTV on CT images. At the axial level, the longitudinal lengths of the GTV were calculated in terms of the number of CT scanning layers.

The measuring and correction of the real tumor length of surgical specimens: the surgical specimens were fixed in 10% formalin for at least 24 h and split along longitudinal axis and the upper and lower boundaries of the lesions were determined. The maximum long diameter of tumor was measured by ruler. Value of 90% ±10% was adopted as shrinkage ratio of tumor specimen after immobilization, and the real tumor lengths were calculated by the formula of tumor surgical specimen length/0.9.[9]

Image analysis and apparent diffusion coefficient calculation

Siemens SYNGO B17 postprocessing working station was used for image analysis and NUMARIS/4 software was used for measuring the relevant parameters.

T1WI and T2WI images were used to determine the location, shape, and necrosis areas of the tumor. ADC values were measured in the ADC images of parenchyma part of the tumor from the slice with largest and most clearly visible tumor, region of interest (ROI). ROI of each ADC image was selected in the same region, if possible, and measured thrice to calculate the mean value. ADC value was finalized in DWI after consensus among the two radiologists.

Statistical analysis

All statistical analyses were performed using SPSS® (SPSS, Chicago, Illinois, USA) version 19.0. The data of ADC values were expressed as X± s. For the CCRT response assessment group, the pre-CRT and the post-CRT ADC values were compared through analysis of variance. For the GTV assessment group, the ESCC length results of measurement with different methods were compared with real length of ESCC after operation through paired sample t-test. The relations between the response evaluation of CCRT and tumor cell apoptosis-positive ratios and correlation between the real length of ESCC and ESCC by imaging were investigated in correlation analysis. P < 0.05 was considered statistically significant.


 > Results Top


Baseline characteristics

We enrolled 18 patients with ESCC (12 men, 6 women; mean age of 53.6 years; age range of 42–61 years) as the CCRT response analysis group to determine efficacy of CCRT in ESCC, who do not have surgery by clinical evaluation and 38 patients (21 men, 17 women; mean age: 64.8 years; age range: 38–78 years) as the GTV assessment group to determine longitudinal length of ESCC. The tumor primary site distributions included upper thoracic (9 patients), middle thoracic (25 patients), and lower thoracic (4 patients).

Therapeutic response

During the analysis of the CCRT response analysis group, 4 of 18 patients were lost to follow-up. Therefore, the final analysis included 14 patients who received CCRT. Among the 14 patients, 2 (14.3%) achieved CR, 9 (64.3%) reported PR, and 3 (21.4%) showed SD-PD and was not reported in any of the patients [Figure 1].
Figure 1: Images of a patient with midesophageal low-differentiated squamous cell carcinoma. (a) Prechemoradiotherapy axial T2-weighted image, the wall of middle segment of esophagus is obviously thickening associated with lumens stenosis. (b-e) Axial T2-weighted images of review at the 1st, 3rd, 5th, and 10th weeks during concurrent chemoradiotherapy show that squamous cell carcinoma is increasingly shrinking

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Pre- and post-chemoradiotherapy apparent diffusion coefficient values

[Table 1] summarizes the ADC values (mm2/s) of the 12 ESCC patients with complete dataset. ADC values were lowest with highest b-values pre-CCR. Further, ADC values significantly increased from pre-CRT to week-10 in MRI-DWI with all the b-values (P < 0.001). However, a decrease was observed after 1-week from pre-CRT in all the groups with different b-values, but it was not statistically significant (P > 0.05). DWI images with b-values of 600, 800, and 1000 s/mm2 at 1st, 3rd, 5th, and 10th weeks during CCRT showed aggravation of anamorphous decrease in the signal-noise ratio (SNR) [Figure 2]a and shrinking of tumor leading to decreased tumor volume with prolongation of treatment [Figure 2]b,[Figure 2]c,[Figure 2]d,[Figure 2]e.
Table 1: Apparent diffusion coefficients values (×10-3 mm2/s, x̄±s) of magnetic resonance diffusion-weighted imaging using different b-values of the esophageal squamous cell carcinoma of 12 patients with complete date preconcurrent chemoradiotherapy and during concurrent chemoradiotherapy at the 1st, 3rd, 5th, and 10th weeks

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Figure 2: Images of a 56-year-old male patient with midesophageal low-differentiated squamous cell carcinoma. (a) Prechemoradiotherapy diffusion-weighted images with b values of 600, 800, and 1000 s/mm2 show that, with increasing b values, the anamorphose is increasingly aggravating and the signal noise ratio of diffusion-weighted imaging is decreasing. (b-e) diffusion-weighted images with b values of 600, 800, and 1000 s/mm2 of review at the 1st, 3rd, 5th, and 10th weeks during concurrent chemoradiotherapy show that the tumor volume shrank with the treatment prolonged. Diffusion-weighted imaging shows that the apparent diffusion coefficient values are slightly decreasing at 1st and thenceforth increasing gradually

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Correlation between tumor cell apoptosis-positive ratios and apparent diffusion coefficients

A positive rate for cell apoptosis ratio was reported. ADC values of MRI-DWI images with different b-values were positively correlated with cell apoptosis positive ratios [Figure 3], with significant correlation achieved with ADC value (b = 600 s/mm2 (P < 0.05), ADC value (b = 800 s/mm2) (P < 0.05) and particularly ADC value (b = 1000 s/mm2) (P < 0.01), thus suggesting the ability of ADC value in reflecting the histopathology changes of tumor tissue after CCRT.
Figure 3: (a-c) Correlation analyses between esophageal carcinoma cell apoptosis-positive ratios and apparent diffusion coefficient values of diffusion-weighted images with different b values

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Esophageal squamous cell carcinoma length measurements

For the GTV assessment group, the comparison of ESCC lengths evaluated using endoscopy, esophageal barium fluoroscopy, CT scan, and DWI at different b-values (400, 600, and 800 s/mm2) and the real length (pathological specimen resected at surgery and calculated by the formula of tumor surgical specimen length/0.9) is presented in [Table 2]. The average length of ESCC ranged from 4.013 to 6.00 cm. MRI-DWI (b = 600 s/mm2 and 400 s/mm2), esophageal barium fluoroscopy, and CT scan reported longer average length of ESCC compared with real length of 4.426 ± 1.256 cm; whereas, the average length reported with endoscopy and MRI-DWI (b = 800 s/mm2) was lower compared with the real length of ESCC. Difference of lengths using all the methods was significantly different from the real length (P < 0.05). There was a high level of agreement between MR-DWI (b = 600s/mm2) measurements of esophageal tumor lengths and real length of ESCC, as shown in [Figure 4].
Table 2: The esophageal squamous cell carcinoma lengths of 38 patients measured by endoscopy, esophageal barium fluoroscopy, computed tomography scan, magnetic resonance imaging-diffusion-weighted imaging at different b values (b=400, 600, and 800 s/mm2) and real length pathological specimen (resected at surgery and calculated by the formula of tumor surgical specimen length/0.9) (cm, x̄±s)

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Figure 4: The measurement of the longitudinal length of gross tumor volume of esophageal squamous cell carcinoma. (a) Measurement of the longitudinal length of pathological specimen of esophageal squamous cell carcinoma. (b) Measurement of the longitudinal length of gross tumor volume of esophageal squamous cell carcinoma with magnetic resonance imaging-diffusion-weighted imaging at different b values (b = 400, 600, and 800 s/mm2) (c) measurement of the longitudinal length of gross tumor volume of esophageal squamous cell carcinoma with coronary reconstruction of multidetector computed tomography. (d) measurement of the length of esophageal squamous cell carcinoma with esophageal barium fluoroscopy

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All the imaging modalities (endoscopy, esophageal barium fluoroscopy, CT scan, and DWI at different b-values) showed significant positive correlation with the real length of ESCC [Table 3].
Table 3: Correlation analyses between the real length of esophageal squamous cell carcinoma (pathological specimen resected at surgery and calculated by the formula of tumor surgical specimen length/0.9) and the esophageal squamous cell carcinoma lengths measured by endoscopy, esophageal barium fluoroscopy, computed tomography, magnetic resonance imaging-diffusion-weighted imaging at different b values (b=400, 600, and 800 s/mm2) of 38 patients

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 > Discussion Top


Esophageal cancer is a common malignant neoplasm of upper digestive tract with a steadily increasing incidence and mortality.[12] Squamous cell carcinoma of esophagus is the most common pathologic type, with characteristic high degree of malignancy, rapid development, poor therapeutic effect, and high recurrence rate.[13] China has one of the highest prevalence rates of EC in the world.[14],[15] Yamada et al. reported 100% possibility of determining the depth in 20 ESCC patients using a 7.0T MRI-DWI.[9] Similarly, Imanishi et al. also reported improved early detection of treatment response in 27 ESCC patients using ADC values. The sensitivity, positive predictive value, and accuracy were 71%, 100%, and 85%, respectively.[10] Study by Lambregts et al. also reported improvement in the detection of therapeutic response after addition of DWI to MRI with high specificity.[16] Further, accurate determination of GTV by measuring longitudinal length of EC MRI-DWI also caused accurate prediction of esophageal GTV length accurately in the study by Hou et al.[17]

Although studies are there to determine the response after chemoradiation therapy in other cancers and in ESCC in other nations,[16],[10] there are limited studies evaluating the efficacy of CRT in ESCC using MRI-DWI in China.[16] Our study is among the very first to determine the efficacy of CCRT using MRI-DWI at different b-values, determination of length of ESCC, and finding correlation between the real length and lengths determined by different imaging techniques.

CRT is currently regarded as the standard treatment for locally advanced ESCC that cannot be radically resected. CT and esophagography imaging have been traditionally used to evaluate the chemo-radiotherapeutic response in ESCC. However, these imaging modalities depend mainly on the morphological changes. In the recent years, functional molecular imaging modality, integrated positron emission tomography (PET)/CT with 2-[18F]-fluoro-2-deoxy-d-glucose (FDG), has been actively studied for its potential value in evaluating the therapeutic response of ESCC after CCRT.[18] It has higher sensitivity and can reflect the activity of tumor cell at the cellular level, but the high costs limit its popularity and utilization.

MRI-DWI is a new noninvasive functional imaging technique used for detecting organizational structures at the microscopic level and is based on the microscopic random translational motion of water molecules in biological tissues. Since DWI reflects the diffusion movement of water in tissues, it could be used to measure the changes in both the shape and function of tumors.[19] There are no obvious distinguishing factors between DWI and the PET/CT in relation to detection of tumor changes at the molecular or cellular level and evaluating the treatment response to CRT in tumors.[20] When the b-value is high, the DWI can be more sensitive to water molecule diffusion and the signal intensity of ESCC is increased compared to the surrounding tissue. However, the higher b-value lowers the SNR of DWI significantly, and the magnetic susceptibility artifact and anatomical distortion are increasingly aggravated.[19] In this study, we obtained DWI images with b-values of 600, 800, and 1000 s/mm2 and measured the ADC values of the ESCC foci. The components of the applied gradients for diffusion weighting were equal in read-out, phase and slice-encoding to obtain the maximum total gradient strength. The DWI images are observed and the tumor cell apoptosis-positive ratios of the pathological specimen were taken as contrast standard. We found that the SNR of DWI images with a b-value of 600 s/mm2 was higher than that of 800 s/mm2 and 1000 s/mm2. Hence, we believe that DWI with b-value of 600 s/mm2 had the highest reliability and was optimized as the reference for tumor delineation of the radiotherapy target for GTV and for measuring the longitudinal length of gross tumor pre- and post-CRT. The ADC values decreased after CCRT for 1 week and we believe it to be due to local obvious inflammation and necrosis of the ESCC. After CCRT for 3 weeks, the ADC value gradually increased and we believe it to be related to the necrosis of the ESCC foci after CCRT, increasing of tumor cell apoptosis, alleviation of the cytotoxic edema, and increase of vasogenic edema.[21] It revealed that the restricted diffusion of tumor tissue is significantly reduced after CCRT. The results of correlation analysis between the ADC value and the tumor cell apoptosis ratio also confirmed that the increasing ADC value positively correlated with the raise of the tumor cell apoptosis-positive ratio. This study also suggested that ADC value can reflect the histopathology changes of the tissue of tumor after CCRT, especially after 2–3 weeks of the therapy.[22] It was also observed that increasing b-value, the SNR of DWI decreased. At present, there are no uniform standards to the selection of the b-values for DWI in ESCC.

Wei C et al. suggested that DWI images using b-value of 500 s/mm2 for the ESCC can obtain satisfactory image SNR, which is similar to our results selecting b-value = 600 s/mm2.[20] In addition, the differences of ADC values using b = 800 s/mm2 were mostly statistically significant. There was a higher significant correlation between ADC values using 1000 s/mm2 and tumor cell apoptosis-positive ratio. It was observed that b-value of 1000 s/mm2 was more beneficial in evaluating chemoradiotherapeutic efficacy and b-value of 800 s/mm2 was beneficial to observe the changes over a period. From this, it can be inferred that the changes of ADC values of ESCC pre- and post-CRT reflect the characteristics of prognosis of tumor. The DWI images obtained from using different b-values can reveal different features of images or tissue after treatment and all of them are valuable for evaluation.[23] Therefore, DWI using multiple b-values can serve as a method to evaluate the chemoradiotherapeutic efficacy of ESCC. Although DWI using high b-values is preferential to distinguish the vasogenic edema and cellular edema, it can also lead to descending of SNR and the aggravation of magnetic susceptibility artifact. At the same time, esophageal imaging is susceptible to the pulsation of heart and aorta and ease to cause the image distortion so as to influence the image observation. For this reason, it is of great significance to give consideration to image quality and evaluation of tumor to determine b-values reasonably.

Accurate measurement of the longitudinal length of GTV of ESCC is crucial to preoperative evaluation and surgical planning. The GTV is the volume of tumor that can be seen on or is visible or can be felt. GTV represents demonstrable extent and location of the malignant growth. Esophageal barium fluoroscopy and endoscopy are the two commonly used modalities to measure the length of ESCC. However, endoscopy underestimates the range of tumor aggressiveness, including the upper and lower margins of the cancerous foci and surrounding circumference. MRI-DWI, as a new functional imaging at the molecular or cellular level, is extremely sensitive to restriction of water molecular movement. It is feasible to use MR-DWI with different b-values to observe the range of restriction of water molecular movement so as to measure the length of ESCC. In this study, we chose MR-DWI with b-values at 400, 600, and 800s/mm2 to measure the longitude length of the GTVs in ESCC compared with other imaging modalities. The length measured from pathological specimen according to shrink ratio was used as the golden standard. The results showed that the length measure from endoscopy is shorter than “golden standard” and it can be inferred that endoscopy cannot observe the invasive range of the ESCC. However, endoscopy detects the early carcinoma or little foci, which are difficult to be observed by the esophageal barium fluoroscopy, routine CT scan, and T2W MRI. Hence, endoscopy is still the indispensable modality of preoperative examination of the ESCC. CT is the primary modality for delineating GTV and planning radiation treatment, but the length of the ESCC is often overestimated.[24] Due to inflammation-induced swell, food persistence, and amplification, esophageal barium fluoroscopy can also overestimate the length of the ESCC. The SNR and the false positive caused by the T2 shine-through effect should be considered when the diffusion-sensitive gradient b-values were taken. When higher b-value is used, DWI is more sensitive to water molecule diffusion and hence lowers SNR of DWI significantly, thereby aggravating magnetic susceptibility artifact and anatomical distortion. This can lead to shortening of average tumor length than the pathological tumor lengths. Among all the measurements, the length measured by MR-DWI (b = 600 s/mm2) was the closest and had a high correlation (r = 0.980, P < 0.05). The difference in measurements was statistically significant (P < 0.05). Wang et al. observed that the esophageal tumor lengths measured by DWI at a b-value of 600 s/mm2 was closely related to the length measured by the surgical specimen and the results were similar to our study.[25] The longitudinal length of GTV of the ESCC is influenced by the magnetic susceptibility artifacts due to the lung tissues with abundant gas on bilateral sides of the esophagus. But, it can be reduced by thin slice scanning, shimming magnetic field, shortening the TE (echo time), and effective fat suppression. Although the endoscopy and esophageal barium fluoroscopy in measuring the length of the esophageal lesions are mainly used, MR-DWI should be recommended because of its superiority. In this study, the slice of MRI-DWI scan is 5 mm. In the subsequent study, 3 mm and even thinner slice scan will be used to improve the accuracy of measurement. Although we think that the experimental data are accurate, the slightly less amount of samples weakens the conviction. These will be improved in the following study.


 > Conclusion Top


From our study, it can be concluded that MR-DWI can be used as an effective tool for evaluating the efficacy of CRT in ESCC. We also evaluated that MRI-DWI with b-value of 600 s/mm2 was capable of measuring the longitudinal length of ESCC and was close to the actual lesion length of the surgical specimen. Hence, it can be used as a supplementary means in measuring the length of the ESCC lesions. However, comprehensive application of various methods could improve the accuracy.

Acknowledgment

The study is supported by the National Natural Science Foundation of China (Grant No. 81271607) and National Postdoctoral Science Foundation of China (Grant No. 2015M572810).

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
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    Figures

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    Tables

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