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Review Utilizing intestinal ultrasound to assess treatment response in ulcerative colitis
Shintaro Sagami1orcid, Taku Kobayashi1,2,3orcid

DOI: https://doi.org/10.5217/ir.2026.00006
Published online: June 1, 2026

1Center for Advanced IBD Research and Treatment, Kitasato University Kitasato Institute Hospital, Tokyo, Japan

2Department of Gastroenterology, Kitasato University Kitasato Institute Hospital, Tokyo, Japan

3Department of Gastroenterology, Kitasato University School of Medicine, Sagamihara, Japan

Correspondence to Shintaro Sagami, Center for Advanced IBD Research and Treatment, Kitasato University Kitasato Institute Hospital, 5-9-1 Shirokane, Minato-ku, Tokyo 108-8642, Japan. E-mail: jaken1013@gmail.com
• Received: January 5, 2026   • Revised: March 29, 2026   • Accepted: April 8, 2026

© 2026 Korean Association for the Study of Intestinal Diseases.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

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  • Intestinal ultrasound (IUS) enables frequent, noninvasive assessment of inflammatory activity in ulcerative colitis and can support treat-to-target decisions without bowel preparation. Evidence from prospective cohorts indicates that early IUS changes within 1 to 2 weeks—particularly reductions in bowel wall thickness and color Doppler vascularity—are associated with short-term response and can guide timely treatment optimization during induction. Follow-up assessments at 6 to 12 weeks further improve risk stratification by reassessing bowel wall thickness and Doppler vascularity, including composite indices such as the Milan Ultrasound Criteria, which correlate with endoscopic outcomes and subsequent medium- to long-term clinical events (e.g., relapse and colectomy). This review synthesizes the most reproducible IUS parameters and proposes a practical, time-windowed monitoring approach integrating IUS with symptoms, biomarkers, and endoscopy, whereby assessments within 1–2 weeks and again at 6–12 weeks provide actionable information to accelerate induction optimization and anticipate later outcomes in ulcerative colitis.
  • Keywords: Inflammatory bowel diseases; Ultrasonography; Recurrence; Biomarkers; Treatment outcome
Ulcerative colitis (UC) is characterized by repeated cycles of relapse that require treatment intervention [1]. Although many therapies have become available for patients in recent years, their therapeutic effects need to be monitored each time [2]. Recently, the utility of intestinal ultrasound (IUS) for treatment monitoring has been widely reported in UC. Indeed, IUS is beneficial not only in diagnosing inflammatory bowel disease and evaluating disease severity [3], in monitoring patients during remission and predicting relapse [4-6], but also to closely monitor disease activity during acute flares and promptly assess therapeutic effect, stemming from its low invasiveness and easily repeatable property. This review will focus on using IUS to evaluate treatment response in UC.
In STRIDE-II, treatment targets are typically assessed in sequence, from symptoms and serum biomarkers to fecal calprotectin, and endoscopic remission [7]. C-reactive protein measured at diagnosis and during follow-up has been shown to reflect subsequent disease activity and systemic inflammation [8]. We have shown that leucine-rich α2-glycoprotein at week 1 after treatment initiation independently predicted endoscopic improvement within 1 year and showed slightly better predictive accuracy than C-reactive protein [9]. Fecal calprotectin has also been reported to serve as a prognostic marker in UC: higher baseline levels predict short-term colectomy, and reductions within 2–8 weeks are strongly associated with treatment success. In addition, higher trough concentrations of biologic agents during the early induction phase—particularly at week 2—have been associated with favorable clinical and endoscopic outcomes [10,11]. However, these tools do not localize residual inflammation or quantify its severity by colonic segment. In contrast, early IUS kinetics can be assessed repeatedly within days to weeks and provide segment-level, transmural information that has been linked not only to endoscopic outcomes but also to medium- to long-term events (e.g., relapse and colectomy) via composite indices such as Milan Ultrasound Criteria (MUC) [12-16].
Endoscopy provides this anatomic and severity information and also carries prognostic value. Early endoscopic improvement after treatment initiation has been associated with subsequent outcomes; for example, in patients treated with cyclosporine, endoscopic improvement by day 14 was associated with higher colectomy-free survival within 1 year [10]. Moreover, across several other studies, post-induction mucosal healing has been consistently shown to be strongly associated with subsequent steroid-free remission and colectomy avoidance [17]. Nevertheless, due to its invasiveness, repeating endoscopy multiple times over a short period is impractical in routine care.
IUS offers several advantages over conventional diagnostic methods for UC. Compared with colonoscopy and capsule endoscopy, it is less expensive, does not require bowel preparation or sedation, and carries no risk of perforation or bleeding (Table 1). Regarding cost, direct reimbursement and out-of-pocket expenses vary widely by healthcare system; to make comparisons more concrete, Table 1 shows representative costs from Japan and the United States of America. Unlike biomarkers, IUS can delineate the extent of inflammation. In addition, studies have shown that patients find IUS more acceptable than endoscopy or stool-based tests with better compliance [18,19]. Nevertheless, IUS has some limitations: visualization may be reduced in patients with obesity, marked bowel gas, or deep pelvic disease, and rectal inflammation can be difficult to assess. Moreover, IUS cannot provide histological information, and therefore cannot evaluate microscopic disease activity, or cytomegalovirus reactivation, which requires tissue sampling and histopathological assessment. Additional practical limitations should be acknowledged, including operator dependency with inter-operator and inter-center variability, which necessitates structured training, supervision, and ongoing quality assurance—conceptually similar to endoscopy training. IUS also has reduced sensitivity for mild or purely mucosal inflammation (particularly in near-remission states) compared with colonoscopy and fecal calprotectin, and therefore should be interpreted in conjunction with fecal calprotectin when the main question is subtle residual activity [20].
Training Burden and Implementation
For clinicians planning to adopt IUS, the main workload is front-loaded training and standardization rather than patient preparation or procedural risk management. Unlike colonoscopy, IUS does not require sedation, bowel preparation, or recovery time, enabling higher assessment frequency (Table 1); however, consistent performance depends on achieving competency and maintaining inter-operator reliability through structured curricula, mentored scanning, and periodic calibration.
Ultrasonographic features in UC are responsive to changes in inflammatory burden with treatment. In particular, prospective monitoring studies, including TRUST&UC study, have demonstrated that key bowel wall parameters improve in parallel with clinical and endoscopic response, supporting IUS as a tool for longitudinal disease assessment (Fig. 1) [4].
1. Bowel Wall Thickness
Bowel wall thickness (BWT) consistently decreases with effective therapy and correlates with endoscopic severity [3,4,14]. Among individual parameters, BWT has the most consistent evidence base as an early indicator of treatment response and subsequent outcomes across disease settings [4,5,21]. In the rectum, changes in BWT assessed by transperineal ultrasound (TPUS) also showed strong performance for predicting short-term symptomatic remission and longer-term outcomes, including clinical-endoscopic remission and histologic healing [12,15].
2. Color Doppler Signal
Mural vascularity assessed by color Doppler (e.g., International Bowel Ultrasound Segmental Activity Score [IBUS-SAS] color Doppler signal [CDS] subscore/modified Limberg score) typically declines with improvement in inflammation and complements structural assessment [4,22]. However, although persistent Doppler activity has been associated with suboptimal endoscopic outcomes, its role as an independent and generalizable early predictor remains less uniformly established than BWT, and is best interpreted in combination with BWT and clinical context [14].
3. Submucosal Index
The submucosal compartment is increasingly recognized as clinically informative in UC. Submucosal index—typically defined as the proportion of submucosal thickness relative to total BWT—has been proposed as a pragmatic way to quantify submucosal expansion and may help differentiate inflammatory versus remodeling-predominant wall thickening and refine response assessment [23].
4. Loss of Bowel Wall Stratification
Loss of bowel wall stratification is a marker of more severe inflammation and may improve with effective therapy [3,14], but in early prediction models it has not shown independent predictive value for endoscopic remission/improvement [14]. Baseline submucosal hyper-echogenicity quantified as relative submucosal echogenicity was higher in endoscopic non-responders than responders, and relative submucosal echogenicity >108 grayscale values predicted treatment non-response in a prospective UC cohort [24].
5. Inflammatory Fat
Hyperechoic inflammatory fat is observed in more severe UC and can improve as inflammatory burden resolves [14]. Unlike Crohn’s disease, convincing data that baseline inflammatory fat independently predicts treatment outcomes in UC are limited; it is therefore best regarded as a marker of disease severity rather than a stand-alone predictor [14].
6. Composite Scores
Composite indices that combine BWT and Doppler vascularity may better capture residual transmural inflammatory burden than single parameters. The MUC is calculated as 1.4×BWT, with 2 additional points when the Doppler signal is present (CDS >0). MUC decreases with effective therapy and has been associated with endoscopic outcomes as well as longer-term risk stratification, including colectomy risk and relapse during clinical remission [6,13,25]. In addition to MUC, other composite indices (e.g., UC-IUS scores and the IBUS-SAS framework, including CDS subscore) can support standardized reporting and longitudinal tracking; however, their predictive performance is not necessarily superior to that of MUC [26], and simpler scores that are easy to calculate may be more practical for routine clinical use. Moreover, their prognostic thresholds and cross-center generalizability in UC remain less established and require further validation.
Transabdominal ultrasound (TAUS) is accurate for detecting colonic inflammation but is less reliable for the rectum. In an individual patient data meta-analysis using colonoscopy as the reference standard, BWT ≥ 3 mm identified inflammation in colonic segments with pooled sensitivity 86.4% and specificity 88.3%, whereas rectal performance was lower (sensitivity 74.5%, specificity 69.5%) [3]. These data support the need for dedicated rectal assessment strategies in UC. TPUS addresses this limitation by enabling direct evaluation of the rectum and has shown good correlation of rectal BWT with endoscopic activity [27,28]. Early improvement in rectal BWT on TPUS appears to be a stronger predictor for better treatment outcomes than sigmoid BWT measured by TAUS [12,15]. However, multicenter validation is still required to standardize acquisition and define reproducible response thresholds, and to quantify the incremental value of TPUS over TAUS in UC [3].
The timing of IUS for treatment monitoring should be tailored to disease severity and lesion distribution (Table 2) [4,6,13-16,21,25,24,29].
1. Immediate Phase (Day 2 to Week 2)
In acute severe UC treated with intravenous corticosteroids, TAUS performed as early as 48 ± 24 hours provides actionable stratification: BWT <3 mm is associated with colectomy avoidance, whereas BWT ≥4 mm identifies patients at high risk of colectomy and subsequent treatment intensification [21]. When rectal assessment is clinically important, early evaluation can be strengthened using TPUS, and a ≥0.5 mm decrease in rectal BWT at week 1 discriminates clinical-endoscopic remission and histologic–endoscopic mucosal improvement (area under the curve, 0.75–0.79) [15].
2. Early Phase (Weeks 4–12)
During induction for moderate-to-severe UC, TAUS changes are informative: normalization of BWT (<3.0–3.1 mm) and/or ≥30% reduction within weeks 2–6 is associated with clinical response at week 12 [4]. At week 6, adding mural vascularity on color Doppler imaging further refines prediction—BWT ≤ 3.0 mm and greater BWT reduction predict favorable endoscopic outcomes, whereas persistent Doppler activity (CDS positivity) is independently associated with failure to achieve endoscopic improvement [14]. At week 12, MUC ≤6.2 is linked to a higher likelihood of endoscopic remission and greater endoscopic improvement during follow-up [13].
3. Intermediate Phase (Beyond Week 12)
For longer-term risk stratification, elevated MUC values have been associated with colectomy risk and clinical relapse even among patients in clinical remission [6,25].
We present a case of a 23-year-old male patient with pancolitis who was refractory to systemic corticosteroids and subsequently started on infliximab plus an immunomodulator for induction therapy. At baseline, IUS demonstrated active inflammation with increased BWT and CDS across segments, and MUC was 9.1. Colonoscopy demonstrated a Mayo endoscopic subscore of 3 with extensive ulceration. At week 2, IUS revealed heterogeneous early kinetics across segments: the descending colon improved (BWT 3.4 mm; CDS 2), whereas the sigmoid colon remained thickened with persistent Doppler activity (BWT 4.3 mm; CDS 2). Rectal disease worsened structurally despite low Doppler activity (BWT 5.6 mm; CDS 1). MUC at week 2 was 8.0. By week 14, IUS showed marked improvement in colonic wall thickening and Doppler activity (descending colon: BWT 1.3 mm; CDS 0; sigmoid colon: BWT 1.8 mm; CDS 0), while rectal findings also improved but remained abnormal (BWT 4.3 mm; CDS 1). MUC at week 14 was 2.5. At week 24, a follow-up colonoscopy confirmed endoscopic remission. Overall, this case illustrates how serial IUS—using segmental BWT/CDS together with MUC—can capture early, segment-specific response patterns and track subsequent improvement aligned with endoscopic healing (Fig. 2). Written informed consent was obtained for publication of the case details and images.
The available evidence supports IUS as a practical, repeatable tool for monitoring treatment response in UC. Early improvement in key ultrasonographic parameters—particularly BWT and composite indices such as MUC—can provide actionable information that complements symptoms and biomarkers and may facilitate timely treatment optimization.
Another important perspective is the role of TPUS as an extension of standard transabdominal IUS. While TAUS performs well for most colonic segments, its diagnostic performance is consistently lower in the rectum, especially in patients with higher body mass indices or deep pelvic disease. TPUS can overcome this limitation by enabling more reliable rectal assessment, and a hybrid TAUS+TPUS strategy may therefore offer a more complete, full-colon evaluation in UC.
Key unmet needs include further prospective, multicenter validation of TPUS-based treatment monitoring (including standardized acquisition protocols, thresholds, and clinically meaningful response definitions), and the integration of TAUS/TPUS outcomes into treat-to-target algorithms alongside biomarkers and endoscopy. Establishing scalable training pathways and quality assurance frameworks will also be essential to broaden implementation and reduce variability across centers.
Practical strategies to facilitate wider adoption include: (1) standardized training programs with competency-based milestones (e.g., supervised case volumes, image portfolio review); (2) certification or credentialing pathways aligned with professional societies; (3) quality assurance measures such as inter-observer agreement exercises, periodic audit of image quality and reporting completeness, and use of structured report templates; and (4) embedding IUS time-points (e.g., week 1–2 and week 6–12) into treat-to-target algorithms alongside symptoms, biomarkers, and confirmatory endoscopy when needed. These steps directly address operator dependency and inter-center variability and are likely prerequisites for scalable implementation.
IUS has proven to be an effective, noninvasive tool for monitoring treatment response in UC. By utilizing ultrasonographic parameters such as BWT and CDS changes, clinicians can more accurately predict treatment outcomes and make timely adjustments to therapeutic strategies. MUC further enhances the utility of IUS by providing a quantitative measure of disease activity, which correlates well with endoscopic findings. Adopting TPUS over traditional transabdominal methods has also improved the accuracy of rectal assessments, offering a more comprehensive view of disease progression and response to treatment. As the use of IUS expands, its integration into clinical practice will play a critical role in advancing the management of UC, ensuring that patients receive optimal, personalized care.

Funding Source

The authors received no financial support for the research, authorship, and/or publication of this article.

Conflict of Interest

Sagami S has served as an advisory board member or speaker for AbbVie, Alimentiv, Eli Lilly, Janssen Pharmaceuticals, Gilead Sciences, Inc., JIMRO Co., Ltd., KISSEI Pharmaceutical Co., Ltd., Kyorin Pharmaceutical Co., Ltd., Mitsubishi Tanabe Pharma Corporation, EA Pharma Co., Takeda Pharmaceutical Co., Ltd., Nippon Kayaku Co., Ltd., and Zeria Pharmaceutical Co., Ltd., and has received research grants from Gilead Sciences, Bristol-Myers Squibb, and Ferring Pharmaceuticals. Kobayashi T served as an advisory board member, consultant, or speaker for AbbVie, Alfresa Pharma, Alimentiv, Bristol-Myers Squibb, Celltrion, Covidien, EA Pharma, Eli Lilly, Ferring Pharmaceuticals, Galapagos, Gilead Sciences, Janssen Pharmaceuticals, JIMRO, Kissei Pharmaceutical, Kyorin Pharmaceutical, Mitsubishi Tanabe Pharma, Mochida Pharmaceutical, Nippon Kayaku, Pfizer, Takeda, and Zeria Pharmaceutical, and has received research funding from AbbVie, Alfresa Pharma, Bristol-Myers Squibb, EA Pharma, Gilead Sciences, Kyorin Pharmaceutical, Mochida Pharmaceutical, Nippon Kayaku, Otsuka Holdings, Pfizer, Sekisui Medical, Samsung, Takeda, and Zeria Pharmaceutical.

Data Availability Statement

Data sharing is not applicable as no new data were created or analyzed in this study.

Author Contributions

Conceptualization; Data curation; Investigation: Sagami S. Methodology: Sagami S, Kobayashi T. Resources: Sagami S. Supervision: Kobayashi T. Visualization: Sagami S. Writing–original draft: Sagami S. Writing–review & editing: all authors. Approval of final manuscript: all authors.

Additional Contributions

The authors would like to express their gratitude to Kazuhiro Odajima (Department of Clinical Laboratory, Kitasato University Kitasato Institute Hospital, Tokyo, Japan) for his invaluable contributions to this project. The authors also thank Michael Dolinger (Department of Pediatrics, NYU Grossman School of Medicine, New York, NY, USA) for his assistance in confirming the approximate costs of diagnostic tests in the United States.

Fig. 1.
Layered structure of the intestinal wall. (A) Intestinal ultrasound image of the sigmoid colon in UC, captured using a 6 MHz convex probe. Five layers are depicted: a hyperechoic boundary from the lumen, a hypoechoic mucosal layer, a hyperechoic submucosal layer, a hypoechoic muscularis propria, and a hyperechoic serosa with its boundary. A color Doppler signal is observed from the mucosal layer to the muscularis, and the haustra has disappeared. (B, C) Transverse view of the sigmoid colon: Loss of the intestinal wall’s layered structure and presence of inflammatory fat (iFat). Increased Color Doppler signal extending beyond the intestinal wall at the same site.
ir-2026-00006f1.jpg
Fig. 2.
Serial IUS and endoscopy during induction therapy in ulcerative colitis. At baseline, IUS demonstrated increased BWT and CDS in the descending colon, sigmoid colon, and rectum. After steroid-refractory disease, infliximab plus an immunomodulator was initiated. At week 2, IUS showed segment-specific early kinetics, followed by marked improvement by week 14. At week 24, colonoscopy confirmed endoscopic remission. IUS, intestinal ultrasound; BWT, bowel wall thickness; CDS, color Doppler signal. Written informed consent was obtained for publication of the case details and images.
ir-2026-00006f2.jpg
Table 1.
Comparison of Noninvasive Tests and Endoscopy for Assessing Disease Activity in Ulcerative Colitis
Technique Endoscopic remission detectionsa Extent mapping (segmental)a Transmural assessmenta Short-interval repeatabilitya Preparation Risk Cost Japanb USAb Limitations
Intestinal ultrasound Moderate High High High None None Low–moderate 13.6 93–796 Poor visibility in the rectum; Affected by body type and bowel gas
Capsule endoscopy Moderate High Low Low Fasting, bowel preparation Capsule retention High 189 1,020–2,768 Low specificity for minute lesions; Unable to perform interventional procedures; Difficulty swallowing
Fecal calprotectin Moderate Low Low Moderate Stool collection None Low 6.9 283 Affected by medications (NSAIDs, PPIs) and other conditions; Limited test frequency
Fecal occult blood test, fecal immunochemical test Moderate Low Low Moderate Stool collection None Low 1.5 49 False positives with anal fissures, hemorrhoids
C-reactive protein Low Low Low High None None Low 4.8 9–44 Often not elevated in mild inflammation
Leucine-rich alpha-2-glycoprotein Low Low Low Moderate None None Low 9.0 NA Limited test frequency
Colonoscopy High High Low Low Fasting, bowel preparation, sedation Perforation, bleeding, infection, sedation High 128 1,856–4,616 Unable to evaluate beyond strictures; small bowel not fully assessed

a Qualitative, clinician-oriented comparison; performance varies by patient population, disease distribution, assay/platform, and local expertise.

b Approximate patient out-of-pocket cost in Japan (USD; assuming a 30% co-payment under Japan’s national health insurance). USD values were calculated at JPY 150 per USD. Representative reimbursement-based estimates; costs vary by payer and setting.

NSAIDs, nonsteroidal anti-inflammatory drugs; PPIs, proton pump inhibitors; NA, not available.

Table 2.
Timing-Based IUS Assessment for Treatment Monitoring in UC
Timing (target) Population/setting Therapy Clinical setting Parameter Numeric threshold/definition Predicted outcome Reference
Baseline Adults with UC (various severities) Various Pre-treatment / baseline stratification RSE in sigmoid colon RSE >108 grayscale values Endoscopic non-response at follow-up (8–26 weeks) [24]
48±24 hours Adults hospitalized with ASUC IV corticosteroids (±rescue) ASUC on IV corticosteroids Colonic BWT BWT <3.0 mm (low risk); BWT ≥4.0 mm (high risk) 12-month colectomy risk and treatment escalation [21]
Week 1 Adults with active UC Advanced therapies (various) Induction (MSUC) Rectal BWT (TPUS) Decrease in rectal BWT ≥0.5 mm Clinical-endoscopic remission and histologic improvement [15]
Weeks 2–6 Adults with MSUC Advanced therapies (various) Induction (MSUC) Sigmoid BWT BWT <3.0–3.1 mm and/or ≥30% reduction Clinical response at week 12 [4]
Week 4 Adults with UC with planned follow-up endoscopy Filgotinib Induction (MSUC) Sigmoid BWT; UC-IUS score; SWE; submucosal echogenicity Early change in BWT and UC-IUS score predicts later endoscopic response Endoscopic response at subsequent endoscopy [16]
Week 6 Adults with MSUC Advanced therapies (various) Induction (MSUC) Sigmoid BWT+CDS Lower BWT and larger % reduction favor response; persistent CDS predicts failure Endoscopic remission/improvement (8–26 weeks) [14]
Week 8 Adults with active MSUC Tofacitinib (10 mg BID) Induction (MSUC) Sigmoid BWT; CDS; MUC BWT cutoff ~3.6 mm for endoscopic healing; MUC also discriminative (study-specific) End-of-induction response classification [29]
Week 12 Adults with UC during induction → early follow-up Biologics Induction (MSUC) MUC Week 12: MUC ≤6.2 Endoscopic improvement during follow-up (~9.4 months) [13]
Medium-term follow-up (≈9–10 months) Adults with UC in clinical remission Various Post-remission monitoring MUC Higher MUC (e.g., >6.2) Relapse risk despite clinical remission [6]
Longer-term risk Adults with UC (across severities) Various Risk stratification MUC vs. MES Higher transmural severity by MUC Colectomy risk prediction [25]

IUS, intestinal ultrasound; UC, ulcerative colitis; RSE, relative submucosal echogenicity; ASUC, acute severe UC; IV, intravenous; BWT, bowel wall thickness; MSUC, moderate-to-severe UC; TPUS, transperineal ultrasound; SWE, shear-wave elastography; CDS, color Doppler signal; BID, twice daily; MUC, Milan Ultrasound Criteria; MES, Mayo endoscopic subscore.

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      Image Image
      Fig. 1. Layered structure of the intestinal wall. (A) Intestinal ultrasound image of the sigmoid colon in UC, captured using a 6 MHz convex probe. Five layers are depicted: a hyperechoic boundary from the lumen, a hypoechoic mucosal layer, a hyperechoic submucosal layer, a hypoechoic muscularis propria, and a hyperechoic serosa with its boundary. A color Doppler signal is observed from the mucosal layer to the muscularis, and the haustra has disappeared. (B, C) Transverse view of the sigmoid colon: Loss of the intestinal wall’s layered structure and presence of inflammatory fat (iFat). Increased Color Doppler signal extending beyond the intestinal wall at the same site.
      Fig. 2. Serial IUS and endoscopy during induction therapy in ulcerative colitis. At baseline, IUS demonstrated increased BWT and CDS in the descending colon, sigmoid colon, and rectum. After steroid-refractory disease, infliximab plus an immunomodulator was initiated. At week 2, IUS showed segment-specific early kinetics, followed by marked improvement by week 14. At week 24, colonoscopy confirmed endoscopic remission. IUS, intestinal ultrasound; BWT, bowel wall thickness; CDS, color Doppler signal. Written informed consent was obtained for publication of the case details and images.

      Fig. 1.

      Fig. 2.

      Utilizing intestinal ultrasound to assess treatment response in ulcerative colitis
      Technique Endoscopic remission detectionsa Extent mapping (segmental)a Transmural assessmenta Short-interval repeatabilitya Preparation Risk Cost Japanb USAb Limitations
      Intestinal ultrasound Moderate High High High None None Low–moderate 13.6 93–796 Poor visibility in the rectum; Affected by body type and bowel gas
      Capsule endoscopy Moderate High Low Low Fasting, bowel preparation Capsule retention High 189 1,020–2,768 Low specificity for minute lesions; Unable to perform interventional procedures; Difficulty swallowing
      Fecal calprotectin Moderate Low Low Moderate Stool collection None Low 6.9 283 Affected by medications (NSAIDs, PPIs) and other conditions; Limited test frequency
      Fecal occult blood test, fecal immunochemical test Moderate Low Low Moderate Stool collection None Low 1.5 49 False positives with anal fissures, hemorrhoids
      C-reactive protein Low Low Low High None None Low 4.8 9–44 Often not elevated in mild inflammation
      Leucine-rich alpha-2-glycoprotein Low Low Low Moderate None None Low 9.0 NA Limited test frequency
      Colonoscopy High High Low Low Fasting, bowel preparation, sedation Perforation, bleeding, infection, sedation High 128 1,856–4,616 Unable to evaluate beyond strictures; small bowel not fully assessed
      Timing (target) Population/setting Therapy Clinical setting Parameter Numeric threshold/definition Predicted outcome Reference
      Baseline Adults with UC (various severities) Various Pre-treatment / baseline stratification RSE in sigmoid colon RSE >108 grayscale values Endoscopic non-response at follow-up (8–26 weeks) [24]
      48±24 hours Adults hospitalized with ASUC IV corticosteroids (±rescue) ASUC on IV corticosteroids Colonic BWT BWT <3.0 mm (low risk); BWT ≥4.0 mm (high risk) 12-month colectomy risk and treatment escalation [21]
      Week 1 Adults with active UC Advanced therapies (various) Induction (MSUC) Rectal BWT (TPUS) Decrease in rectal BWT ≥0.5 mm Clinical-endoscopic remission and histologic improvement [15]
      Weeks 2–6 Adults with MSUC Advanced therapies (various) Induction (MSUC) Sigmoid BWT BWT <3.0–3.1 mm and/or ≥30% reduction Clinical response at week 12 [4]
      Week 4 Adults with UC with planned follow-up endoscopy Filgotinib Induction (MSUC) Sigmoid BWT; UC-IUS score; SWE; submucosal echogenicity Early change in BWT and UC-IUS score predicts later endoscopic response Endoscopic response at subsequent endoscopy [16]
      Week 6 Adults with MSUC Advanced therapies (various) Induction (MSUC) Sigmoid BWT+CDS Lower BWT and larger % reduction favor response; persistent CDS predicts failure Endoscopic remission/improvement (8–26 weeks) [14]
      Week 8 Adults with active MSUC Tofacitinib (10 mg BID) Induction (MSUC) Sigmoid BWT; CDS; MUC BWT cutoff ~3.6 mm for endoscopic healing; MUC also discriminative (study-specific) End-of-induction response classification [29]
      Week 12 Adults with UC during induction → early follow-up Biologics Induction (MSUC) MUC Week 12: MUC ≤6.2 Endoscopic improvement during follow-up (~9.4 months) [13]
      Medium-term follow-up (≈9–10 months) Adults with UC in clinical remission Various Post-remission monitoring MUC Higher MUC (e.g., >6.2) Relapse risk despite clinical remission [6]
      Longer-term risk Adults with UC (across severities) Various Risk stratification MUC vs. MES Higher transmural severity by MUC Colectomy risk prediction [25]
      Table 1. Comparison of Noninvasive Tests and Endoscopy for Assessing Disease Activity in Ulcerative Colitis

      Qualitative, clinician-oriented comparison; performance varies by patient population, disease distribution, assay/platform, and local expertise.

      Approximate patient out-of-pocket cost in Japan (USD; assuming a 30% co-payment under Japan’s national health insurance). USD values were calculated at JPY 150 per USD. Representative reimbursement-based estimates; costs vary by payer and setting.

      NSAIDs, nonsteroidal anti-inflammatory drugs; PPIs, proton pump inhibitors; NA, not available.

      Table 2. Timing-Based IUS Assessment for Treatment Monitoring in UC

      IUS, intestinal ultrasound; UC, ulcerative colitis; RSE, relative submucosal echogenicity; ASUC, acute severe UC; IV, intravenous; BWT, bowel wall thickness; MSUC, moderate-to-severe UC; TPUS, transperineal ultrasound; SWE, shear-wave elastography; CDS, color Doppler signal; BID, twice daily; MUC, Milan Ultrasound Criteria; MES, Mayo endoscopic subscore.

      Table 1.

      Table 2.

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