Keywords
rectal cancer - colonoscopy - MR imaging - transrectal biplane ultrasound - extended
field of view technology
Introduction
The persistently high incidence and mortality rates of colorectal cancer remain a
significant global health concern. According to authoritative statistical data [1], the United States will experience a
significant rise in the number of newly diagnosed colorectal cancer cases, reaching
approximately 152,810 cases by 2024, thus making it the fourth most prevalent
malignancy with the second highest mortality rate. Notably, rectal cancer comprises
a substantial proportion of these cases, with an estimated 46,220 new cases
annually, ranking second among newly diagnosed malignancies in the digestive system.
Moreover, the incidence of rectal cancer has also been increasing rapidly in recent
decades, particularly among younger individuals [2]. This trend poses a significant threat to individual health and
quality of life, while also imposing a considerable burden on the social
economy.
Despite significant advancements in treatment [3], rectal tumors situated in various anatomical positions exhibit
notable variations in treatment options, associated complications, pathological
responses, and ultimate prognosis [4]
[5]
[6]. The
disparities directly impact the quality of life of patients [7]. Among these considerations, precise
measurement of the distance from the lowest boundary of the rectal tumor to the anal
verge (DTAV) is a crucial factor in surgical planning [8]. The European Society for Medical Oncology
(ESMO) classifies rectal cancer based on DTAV, distinguishing between low-position
rectal cancer (≤5 cm), mid-position rectal cancer (>5–10 cm), and high-position
rectal cancer (>10–15 cm) [9]. Typically,
for early-stage rectal cancer with a DTAV less than 8 cm, transanal resection
surgery is often the preferred surgical approach. For cT2~4N0~2M0 stage mid- to
high-position rectal cancer, laparoscopic anterior resection surgery with annus
preservation is routinely performed. Conversely, in the case of low-position rectal
cancer, abdominoperineal rection surgery is often necessary due to the challenges
associated with anus preservation [10].
Despite the importance of determining DTAV, there is currently no definitive best
method to accurately measure it. In clinical practice, the measurement of DTAV
commonly involves methods such as digital rectal examination (DRE), magnetic
resonance imaging (MRI), and colonoscopy. While DRE offers simplicity and
convenience for initial assessment, its accuracy in detecting mid-to high-position
rectal tumors is limited by the finger length of the examiner and the anatomical
features of the patient. Additionally, the subjective nature of DRE assessments can
introduce variability. MRI, a noninvasive and nonradioactive technology, plays a
pivotal role in tumor localization and staging. However, there is currently no
unified standard for positioning the anal verge and for measuring methods in this
context [11]
[12]
[13]. Rigid sigmoidoscopy, on the
other hand, provides a direct approach to examining and measuring tumor height,
earning it the status of a gold standard for DTAV measurement. However, this method
is associated with patient discomfort and limitations regarding insertion depth. In
contrast, colonoscopy, with its flexible endoscope, has significantly improved
patient comfort compared to sigmoidoscopy, gradually emerging as the preferred
method for DTAV measurement [14]
[15]. Nevertheless, measurement errors may still
occur if the endoscope is not aligned parallel to the rectal cavity. Therefore, it
is crucial to ensure proper endoscope positioning and to consider these limitations
when interpreting colonoscopy results for DTAV measurement.
With remarkable advancements in ultrasound technology, the introduction of innovative
equipment, such as intracavitary end-fire probes, intracavitary biplane probes, and
intracavitary 360° annular array probes, has underscored the pivotal role of
ultrasound in rectal cancer diagnosis, staging, and therapeutic evaluation [16]. However, when it comes to measuring DTAV,
the limited field of view of traditional ultrasound probes poses a challenge, with
the comprehensive visualization of the sonographic image from the lowest boundary
of
the rectal tumor to the anal verge being impeded. Consequently, in practical
scenarios, sonographers frequently need to combine multiple images to estimate the
DTAV, which inevitably introduces measurement uncertainties. With the advancement
of
intracavitary biplane probes, ultrasound extended field of view (EFOV) imaging
technology has emerged, leveraging the linear array mode of the intracavitary
biplane probe. This technology incorporates advanced computer image processing
techniques, enabling sonographers to continuously capture and process images through
dynamic probe movements. By building upon traditional ultrasound imaging, EFOV
imaging technology expands the imaging range, thereby facilitating comprehensive
display of the tumorʼs involved length. This, in turn, establishes a robust
foundation for precise DTAV measurement.
Previous research on EFOV imaging technology had primarily focused on measuring
muscle length, area, and rectus abdominis curl angle [17]
[18]
[19], and it was generally recognized as a
reliable evaluation method for distance measurement beyond the length of the
ultrasound probe. However, the application of EFOV imaging technology in rectal
measurements, specifically for assessing the DTAV, remained uncharted territory.
Consequently, this study aimed to explore the clinical application value of EFOV
imaging technology within transrectal biplane ultrasound for measuring DTAV in
rectal cancer.
Materials and Methods
Study Subjects
This study enrolled 84 patients who underwent rectal cancer staging diagnosis in
the Ultrasound Medical Department from August 2022 to January 2024. Prior to the
ultrasound examination, all patients had been definitively diagnosed with rectal
cancer by means of colonoscopy and pathological examination. The exclusion
criteria comprised: (1) 2 patients with tumors positioned too high for clear
visualization due to the limited length of the intracavitary probe; (2) 4
patients with large tumors causing significant stenosis of the rectal lumen,
impeding smooth insertion of the intracavitary probe into the rectal lumen; and
(3) 8 patients who had not undergone MRI examination at our institution. As a
result, the final study cohort comprised 70 patients with rectal cancer, ranging
in age from 36 to 86 years, with a median age of 66 (IQR: 58, 77) years. The
study employed a prospective data collection methodology, which was followed by
a retrospective analysis, and approval for the study was obtained from the
hospital ethics committee.
Ultrasound Image Acquisition
The DTAV measurement was conducted using the EFOV imaging technology on the
Mindray Resona 9 ultrasound system (Shenzhen Mindray Bio-Medical Electronics,
Shenzhen, Guangdong Province, China), employing the ELC13–4U intracavitary
biplane probes with a frequency range of 3.5–9.5 MHz for the convex array and
3.2–12.8 MHz for the linear array. Prior to the examination, patients underwent
bowel cleansing via enema administration (110 mL of glycerol) administered
through the rectum, one hour beforehand. During the procedure, the patient was
positioned in the left lateral decubitus position, with hips and knees flexed,
and the anus was fully exposed by separating the buttocks using the patientʼs
right hand. The probe surface was coated with an adequate amount of coupling
agent and subsequently covered with a latex sheath to guarantee optimal contact.
Air was expelled from the sheath, and an additional layer of coupling agent was
applied to its exterior.
The rectal ultrasound examination, utilizing the intracavitary biplane probe, was
conducted by a seasoned sonographer with over two decades of expertise in
transrectal ultrasonography. During the examination, dynamic grayscale images of
the rectal tumor in both convex array and linear array modes were obtained. In
the lithotomy position, the specific location of rectal tumors was marked and
recorded using the clock face notation. In both scanning modes, the location of
the tumorʼs lowest point was determined and verified independently. Upon
confirmation of this location, the EFOV imaging function was activated in linear
array probe mode by locating and clicking the panoramic imaging button on the
ultrasound diagnostic equipmentʼs operating interface. During image acquisition,
the probe was firmly pressed against the contralateral intestinal wall, with the
surface of the linear array probe gently contacting the rectal wall on the side
to be measured to ensure good coupling. Subsequently, following the preset
direction and speed, the probe was smoothly and evenly moved from the tumorʼs
upper edge to its lowest point and continued downward until the gas line at the
anal edge was visible. Throughout this process, the real-time generation of the
panoramic image on the screen was monitored to ensure completeness, clarity, and
absence of significant distortion or artifacts. Based on the specific
examination circumstances, parameters such as gain, time gain compensation,
depth, and contrast were adjusted as necessary to achieve optimal panoramic
image quality, clearly displaying the details and boundaries of tissues and
organs.
The entire measurement procedure was repeated three times, capturing grayscale
images for each repetition. During each repetition, the distance DTAV was
measured ([Fig. 1]). After these
measurements, the maximum DTAV value obtained by ultrasound (USmax),
the middle DTAV value obtained by ultrasound (USmid), and the minimum
DTAV value obtained by ultrasound (USmin) were recorded. The mean
DTAV value obtained by ultrasound (USmean) was subsequently
calculated based on these recorded measurements. It was important to note that
the sonographer was blinded to the DTAV measurements derived from MRI and
colonoscopy, ensuring the independence and reliability of the ultrasound-based
measurements.
Fig. 1 DTAV measurement is performed using EFOV imaging technology
with an intracavitary biplane probe. The yellow line indicates the
distance from the lowest boundary of the rectal tumor to the anal
verge.
MRI protocol and measurements
During rectal MRI examinations, the German Siemens Skyra 3.0T superconducting MRI
scanner, equipped with an 18-channel body array coil, was deployed to guarantee
exceptional image quality. Specifically, for imaging the sagittal plane,
high-resolution turbo spin echo T2-weighted imaging (TSE-T2WI) technology was
utilized. The scanning parameters were set as follows: repetition time (TR)
3200 ms, echo time (TE) 73 ms, slice thickness 3.0 mm, slice gap 10%, field of
view (FOV) 150 mm x 150 mm, and a matrix optimized to 320 x 224 for enhanced
image detail and clarity.
An experienced radiologist with nine years of experience conducted a
retrospective review of the pelvic MRI images stored in the picture archiving
and communication system. The assessment focused on the precise measurement of
DTAV, defined as the distance from the anal verge to the lowest boundary of the
tumor, utilizing sagittal T2-weighted images. The radiologist traced the rectal
pathway using polyline measurements from the anal verge to the tumorʼs inferior
margin, adding the values to calculate the exact distance between these
anatomical landmarks ([Fig. 2]). It was
important to emphasize that, during this process, the radiologist was unaware of
the DTAV results derived from the ultrasound and colonoscopy measurements.
Furthermore, the study gathered DTAV data from MRI reports authored by
radiologists with varying degrees of experience, ensuring that the radiologist
responsible for the current measurements remained blinded to the information
contained in those reports.
Fig. 2 On sagittal T2-weighted MRI images, the DTAV is measured by
tracing a yellow polyline along the rectal tract, and the cumulative
length of this line is then used to determine the distance from the
lowest margin of the rectal tumor to the anal verge.
Colonoscopy Data Collection
The DTAV data, obtained through flexible colonoscopy, was meticulously gathered
by thoroughly reviewing the medical records of the patients.
Statistical Analysis
The collected data were systematically organized and comprehensively analyzed
using SPSS 27.0 software. Accurate and informative charts and graphs were
created with GraphPad Prism 9. For continuous variables exhibiting normal
distribution, descriptive statistics were presented as mean±standard deviation.
Conversely, for those displaying non-normal distribution, the median and
interquartile ranges were used for characterization. Categorical variables were
quantitatively represented by frequency (n) and percentage (%).
To assess the statistical significance of differences in DTAV measurements across
technologies, the paired t-test was applied, with a P-value less
than 0.05 indicating statistical significance. The consistency of continuous
variables was rigorously evaluated using the intraclass correlation coefficient
(ICC). ICC values≥0.75 indicated exceptional consistency, 0.4 to 0.75 suggested
moderate to good consistency, and values<0.4 indicated poor consistency.
Furthermore, scatter plots were constructed to visually represent the
correlation between data points, thereby enhancing the interpretability of the
results.
Results
General Information
A thorough pathological analysis was conducted on 70 patients, either via
colonoscopy biopsy or surgical resection. The diagnosis identified 69 cases of
rectal adenocarcinoma and a single case of neuroendocrine carcinoma. Among these
patients, 29 underwent surgical intervention, 29 received neoadjuvant therapy,
and 12 were assessed for their response to neoadjuvant therapy ([Table 1]).
Table 1 General patient information.
|
Variable
|
Values
|
|
AGE (years)
|
66 (58, 71)
|
|
Sex
|
|
Male
|
46 (65.7%)
|
|
Female
|
24 (34.3%)
|
|
USmean DTAV (cm)
|
5.17 (3.29, 7.20)
|
|
MRI DTAV (cm)
|
4.85 (2.88, 6.63)
|
|
Colonoscopy DTAV (cm)
|
5.00 (3.00, 7.00)
|
|
cT staging
|
|
cT1
|
5 (7.1%)
|
|
cT2
|
7 (10%)
|
|
cT3
|
50 (71.4%)
|
|
cT4
|
8 (11.4%)
|
|
Pathology
|
|
Adenocarcinoma
|
69 (98.6%)
|
|
Neuroendocrine carcinoma
|
1 (1.4%)
|
|
Measures
|
|
Surgery
|
29 (41.4%)
|
|
NCRT
|
29 (41.4%)
|
|
After NCRT
|
12 (17.1%)
|
|
The lowest tumor point
|
|
Anterior wall
|
37 (52.9%)
|
|
Posterior wall
|
33 (47.1%)
|
A Comparative Analysis of DTAV Measurements Obtained Through Different
Technologies
The analysis showed that the difference between USmean and colonoscopy
DTAV measurements was statistically insignificant, with a discrepancy of 0.22 cm
(t=1.999, p=0.050). Conversely, a significant statistical
difference was observed between USmean and MRI DTAV measurements,
with a discrepancy of 0.48 cm (t=4.621, p<0.001). Similarly, a
significant statistical difference was observed between MRI and colonoscopy DTAV
measurements, with a discrepancy of − 0.26 cm (t=− 2.504,
p=0.015). The results were summarized in [Table 2].
Table 2 A comparative analysis of discrepancies in DTAV
measurements derived from three distinct methods.
|
Variable
|
MD
|
SD
|
t
|
P
|
|
US
mean
-Colonoscopy
|
0.22
|
0.91
|
1.999
|
0.050
|
|
US
mean
-MRI
|
0.48
|
0.87
|
4.621
|
< 0.001
|
|
MRI-Colonoscopy
|
− 0.26
|
0.87
|
− 2.504
|
0.015
|
MD: Differential value of DTAV measurements obtained from two examination
methods.
Consistency of DTAV Measurements across Diverse Methodologies
[Fig. 3] presents scatter plots, and [Fig. 4] presents Bland-Altman plots, both
of which clearly illustrate the consistency among the three measurement
technologies. Additionally, the ICC values presented in [Table 3] indicate a high degree of
agreement across all pairwise measurement methods.
Fig. 3 Scatter plots highlighted the favorable consistency in
pairwise comparisons of DTAV measurements derived from three distinct
methods.
Fig. 4 Bland-Altman plots highlighted the favorable consistency in
pairwise comparisons of DTAV measurements derived from three distinct
methods.
Table 3 A comparative analysis of the consistency in
pairwise DTAV measurements derived from three distinct
methods.
|
Variable
|
ICC (95% CI)
|
|
USmean and MRI
|
0.948 (0.917−0.967)
|
|
USmean and Colonoscopy
|
0.942 (0.908−0.963)
|
|
MRI and Colonoscopy
|
0.943 (0.910−0.964)
|
Assessment of the Reproducibility of Ultrasound-Based DTAV
Measurements
The median DTAV values from ultrasound measurements were 5.05 cm (range:
3.25–7.03 cm) for the minimum (USmin), 5.10 cm (range: 3.25–7.20 cm)
for the middle (USmid), and 5.30 cm (range: 3.38–7.33 cm) for the
maximum (USmax). The median differences in DTAV measurements between
USmax and USmin, USmid and
USmin, as well as USmax and USmid were 0.2 cm,
0.1 cm, and 0.1 cm, respectively. Notably, the consistency between
USmin and USmid, USmin and
USmax, as well as USmax and USmid was
excellent, with all ICC values reaching a value of 0.999 ([Table 4]).
Table 4 Assessment of the reproducibility of
ultrasound-based DTAV measurements.
|
Variable
|
ICC (95% CI)
|
|
USmin and USmid
|
0.999 (0.999−1.000)
|
|
USmin and USmax
|
0.999 (0.998−0.999)
|
|
USmax and USmid
|
0.999 (0.999−1.000)
|
Assessment of the Repeatability of MRI DTAV Measurements
MRI reported an average DTAV value of 5.0 cm (range: 3.00–7.00 cm). Upon
re-measurement by the radiologist, the median DTAV value was 4.85 cm (range:
2.88–6.63 cm). The consistency between these two measurements was outstanding,
attaining an ICC value of 0.985 (95%CI: 0.975–0.990).
Discussion
This study marked the first application of EFOV imaging technology in transrectal
biplane ultrasound for measuring DTAV in rectal cancer patients. The findings
revealed that, when the transrectal biplane ultrasound linear array probe was
employed, EFOV imaging technology not only fully visualized the entire length of the
tumor but also offered a clear panoramic view that surpassed the physical
limitations of the probe, encompassing the region extending from the lower margin
of
the tumor to the anal verge gas line. As a result, the precision and reliability of
DTAV measurements were substantially enhanced.
To ensure the authenticity and reliability of this study, colonoscopy data were
gathered by endoscopists with varying levels of experience, reflecting real-world
clinical settings. The results showed that there was no statistically significant
difference between USmean and colonoscopy in DTAV measurements
(t=1.999, p=0.050), suggesting that ultrasound measurements were
comparable to colonoscopy results. This minor discrepancy between the two methods
was probably due to random error. However, a significant difference was observed
between USmean and MRI in measuring DTAV (t=4.621,
p<0.001), and similarly, a statistically significant difference was found
between MRI and colonoscopy in DTAV measurements (t=− 2.504, p=0.015).
In this study, patients were positioned in the left lateral decubitus position for
both ultrasound and colonoscopy examinations, whereas for MRI, they were scanned in
the supine position. This difference in body positioning may have influenced the
test results. Matthias et al. [20] conducted a
study on tumor height measurement using rigid rectoscopy. They found good
consistency between two researchers when measuring tumor height in the left lateral
decubitus position. However, consistency was only moderate when measuring in the
lithotomy position.
Jacobs et al. [21] conducted a study involving
211 patients and found that although MRI demonstrated good agreement with
colonoscopy when measuring DTAV (ICC=0.7, 95% CI: 0.7–0.8), the values obtained were
significantly smaller than those obtained by colonoscopy, with a difference of 2.5
cm (95% CI: 2.1–2.8). Similarly, Basendowah et al. [14] also found good consistency between MRI and colonoscopy when
measuring DTAV (ICC=0.89, 95% CI: 0.48–0.99), but MRI measurements were smaller by
1.52 cm compared to colonoscopy. The results of this current study also exhibited
a
similar trend, showing that MRI-measured DTAV values were smaller than those of
colonoscopy, with a difference of − 0.26 cm. Furthermore, this study found that the
average ultrasound measurements were higher than those of MRI, with a difference of
0.48 cm. The analysis indicated that the differences in DTAV measurements may have
originated from the varying measurement methods employed. Specifically, flexible
colonoscopy necessitated air insufflation into the colonic lumen prior to
examination. The flexibility of the colonoscope may have resulted in an elongation
of the actual path distance traversed during clinical manipulation, thereby leading
to larger DTAV measurements. In contrast, MRI calculated DTAV by drawing polylines
along the sagittal plane of the evacuated rectal cavity and adding up the lengths
of
these polylines. Given the typical curved folds of the rectum, there were subjective
differences among radiologists when identifying the turning points of the polylines.
Furthermore, measuring along the polyline of the rectal lumen underestimated the
length of the curved lumen, ultimately leading to MRI measurements being lower than
the actual DTAV values.
During image acquisition, the ultrasound probe remained in contact with the rectal
wall while being slid from the lowest point of the tumor to the edge of the anus.
Therefore, ultrasound DTAV measurements were based on the state of the flattened
intestinal wall. Previous scholars [22] had
used MRI T2 sagittal images to delineate along the contour of the intestinal wall
to
determine the height of the tumor, which shared some similarity with ultrasound
measurement. Their study revealed that the average tumor height, as measured by
endoscopy, was (5.9±2.9) cm, whereas the average tumor height, as measured by MRI
images, was (6.2±3.0) cm. When measured along the flattened intestinal wall on MRI
images, the average tumor height was found to be greater than that obtained through
endoscopy. This conclusion was in agreement with the findings obtained through the
ultrasound measurement method employed in this study.
This study also revealed that the ICC values for DTAV measurements between
USmean and colonoscopy, MRI and colonoscopy, and USmean
and MRI were 0.942 (95% CI: 0.908–0.963), 0.943 (95% CI: 0.910–0.964), and 0.948
(95% CI: 0.917–0.967), respectively. These findings underscored the remarkable
consistency among the three methods when measuring DTAV, establishing them all as
dependable instruments for this measurement. Additionally, the study by Serracantet
al. [23] echoed this sentiment. Their research
findings further emphasized the high degree of reliability associated with MRI, EUS,
and colonoscopy in evaluating DTAV. Specifically, when evaluating DTAV, the ICC
between intraoperative rigid rectoscopy (IRR) and MRI was 0.870 (95% CI:
0.757–0.931), between IRR and EUS was 0.981 (95% CI: 0.968–0.989), and between IRR
and colonoscopy was 0.872 (95% CI: 0.770–0.928).
From an ethical standpoint, this study considered it unethical to conduct multiple
examinations by various individuals on the same patient, as it would cause
unnecessary pain and impose an additional burden on the patient. Consequently, in
this study, each patient underwent three repeated measurements conducted solely by
one experienced sonographer, with no comparisons made among measurements by
different sonographers. The consistency among these measurements was excellent,
achieving an ICC of 0.999 for each. These findings strongly support the
reproducibility of transrectal biplane ultrasound in DTAV measurements.
Additionally, our study evaluated the consistency between re-measured MRI DTAV data
by a single radiologist and previous DTAV data reports. The results exhibited
excellent agreement, with an ICC of 0.985 (95%CI: 0.975–0.990), indicating the high
reproducibility of MRI in DTAV measurements. Given its cost-effectiveness, ease of
operation, and superior resolution, we recommend that transrectal biplane ultrasound
EFOV imaging technology should be considered the preferred and crucial method for
measuring DTAV in patients with rectal cancer.
Several limitations were identified in the study. Firstly, the retrospective research
design precluded the use of a single endoscopist for colonoscopy, potentially
compromising the accuracy and reproducibility of colonoscopy outcomes. Secondly,
clinicians in clinical practice may have exhibited biases in their choice of
ultrasonography, particularly a tendency to avoid performing it on patients with
high-position rectal cancer, which could have introduced biases into the research
findings. Furthermore, the sample size was relatively modest, and the study lacked
support from multicenter investigations. Additionally, when applying EFOV imaging
technology, differences in the starting points and movement paths chosen by various
ultrasound physicians could have introduced bias into the images. Therefore, future
studies should consider expanding the sample size and initiating multicenter
collaborations to enhance their credibility and reliability.
In conclusion, transrectal biplane ultrasound with EFOV imaging technology
demonstrated remarkable accuracy and reproducibility when measuring DTAV. This
technology not only addressed the previous lack of ultrasound-based methods for DTAV
measurement but also introduced an efficient and practical new approach for clinical
DTAV assessment. Consequently, this study concluded that transrectal biplane
ultrasound with EFOV imaging technology possessed significant clinical application
value and merited widespread promotion and adoption.
Bibliographical Record
Yan Zhang, Lu Liang, Huachong Ma, Jiagang Han, Xiuzhang Lv, Huiyu Ge. Evaluating Extended
Field of View Imaging for Measuring Rectal Tumor
Lowest Boundary to Anal Verge Distance via Transrectal Biplane
Ultrasound. Ultrasound Int Open 2025; 11: a25696939.
DOI: 10.1055/a-2569-6939
