Evolution of imaging in rectal cancer: multimodality imaging with MDCT, MRI, and PET

Imaging Assessment of the Response to Neoadjuvant Treatment in Rectal Cancer in Relation to Postoperative Pathological Outcomes

BACKGROUND AND OBJECTIVE

Rectal cancer remains a global health challenge with significant morbidity and mortality. Neoadjuvant therapy (NAT) is critical for downstaging tumors and improving surgical outcomes. This study aimed to compare the performance of magnetic resonance imaging (MRI) and computed tomography (CT) in evaluating tumor response to NAT in rectal cancer patients, focusing on imaging accuracy and correlation with histopathological findings.

MATERIALS AND METHODS

This retrospective study analyzed 201 patients diagnosed with rectal cancer who underwent NAT followed by surgery. Imaging evaluations were conducted pre-NAT and post-NAT using MRI or CT. Tumor responses were categorized into complete response, downstaging, stable disease, and upstaging. Statistical analyses included Chi-square, Mann-Whitney U, and Z-tests to assess differences in imaging performance and concordance with pathological outcomes.

RESULTS

Both imaging modalities identified significant downstaging post-NAT, with CT demonstrating a higher sensitivity for detecting complete responses (12.5% vs. 6.61% for MRI) and better local staging accuracy. CT showed superior performance in systemic metastasis detection but had limitations in distinguishing fibrosis from residual tumors. Overall diagnostic accuracy was 42.29%, with MRI having a statistically significant edge in detecting favorable tumor responses (p=0.043). The combined use of CT and MRI provided complementary insights, enhancing clinical decision making.

CONCLUSIONS

MRI excels in local tumor evaluation post-NAT, offering detailed imaging crucial for surgical planning and conservative strategies like "watch-and-wait" in complete responders. CT remains indispensable for systemic staging and metastasis detection. Integrating both modalities within a standardized protocol can optimize staging accuracy and treatment outcomes in rectal cancer.

A Review on Emerging Techniques for Diagnosis of Colorectal Cancer

Common detection methods in practice for diagnosing colorectal cancer (CRC) are painful and invasive leading to less participation of individuals for CRC diagnosis. Whereas, improved or enhanced imaging systems and other minimally invasive techniques with shorter detection times deliver greater detail and less discomfort in individuals. Thus, this review is a summary of the diagnostic tests, ranging from the simple potential use in developing a flexible CRC treatment to the patient's potential benefits in receiving less invasive procedures and the advanced treatments that might provide a better assessment for the diagnosis of CRC and reduce the mortality related to CRC.

Lymph Nodes Evaluation in Rectal Cancer: Where Do We Stand and Future Perspective

The assessment of nodal involvement in patients with rectal cancer (RC) is fundamental in disease management. Magnetic Resonance Imaging (MRI) is routinely used for local and nodal staging of RC by using morphological criteria. The actual dimensional and morphological criteria for nodal assessment present several limitations in terms of sensitivity and specificity. For these reasons, several different techniques, such as Diffusion Weighted Imaging (DWI), Intravoxel Incoherent Motion (IVIM), Diffusion Kurtosis Imaging (DKI), and Dynamic Contrast Enhancement (DCE) in MRI have been introduced but still not fully validated. Positron Emission Tomography (PET)/CT plays a pivotal role in the assessment of LNs; more recently PET/MRI has been introduced. The advantages and limitations of these imaging modalities will be provided in this narrative review. The second part of the review includes experimental techniques, such as iron-oxide particles (SPIO), and dual-energy CT (DECT). Radiomics analysis is an active field of research, and the evidence about LNs in RC will be discussed. The review also discusses the different recommendations between the European and North American guidelines for the evaluation of LNs in RC, from anatomical considerations to structured reporting.

Role of MRI‑based radiomics in locally advanced rectal cancer (Review)

Colorectal cancer is the third most common type of cancer, with high morbidity and mortality rates. In particular, locally advanced rectal cancer (LARC) is difficult to treat and has a high recurrence rate. Neoadjuvant chemoradiotherapy (NCRT) is one of the standard treatment programs of LARC. If the response to treatment and prognosis in patients with LARC can be predicted, it will guide clinical decision‑making. Radiomics is characterized by the extraction of high‑dimensional quantitative features from medical imaging data, followed by data analysis and model construction, which can be used for tumor diagnosis, staging, prediction of treatment response and prognosis. In recent years, a number of studies have assessed the role of radiomics in NCRT for LARC. MRI‑based radiomics provides valuable data and is expected to become an imaging biomarker for predicting treatment response and prognosis. The potential of radiomics to guide personalized medicine is widely recognized; however, current limitations and challenges prevent its application to clinical decision‑making. The present review summarizes the applications, limitations and prospects of MRI‑based radiomics in LARC.

Radiological staging of rectal cancer in a resource limited setting

Objective

Current guidelines on rectal cancer (RC) management recommend pre-operative MRI for loco-regional staging and CT for staging of metastases. This allows appropriate selection of patients for chemo-radiotherapy (CRT). However, MRI is not freely available in many low-income countries. We assessed the status of pre-operative imaging for RC in Sri Lanka and evaluated the performance of CT in RC staging.

Results

A pre-tested interview-administered questionnaire was used to assess the pre-operative use of MRI and CT in RC. CT findings from 37 RC patients were then compared with histopathology findings. Of the 64 surgeons interviewed, 57 (89.1%) did not request an MRI for their RC patients. Reasons cited included limited availability and long waiting times due to competing health needs. A CT was requested by all. In RC, the overall accuracy of CT for T staging was 43.2% and 29.7% of T1–T2 tumours were over-staged as T3. The overall accuracy of CT for regional lymph node staging was 70.3%. In summary, CT alone is not suitable for RC staging in any setting. It leads to over-staging and patients may thus receive unnecessary CRT. Steps must be taken to improve access to pre-operative MRI among Sri Lankan RC patients.

Computerized Tomography Criteria as a Tool for Simplifying the Assessment of Locally Advanced Rectal Cancer

BACKGROUND

Rectal cancer represents a leading cause of mortality worldwide. Staging defines the local and distant extent of the disease, guides management, and predicts prognosis. Different modalities are available for staging including TRUS (transrectal ultrasound), CT (computed tomography), and MRI (magnetic resonance imaging).

OBJECTIVE

The objective of this study was to screen and isolate CT imaging parameters suggestive of advanced rectal cancer and its utility as a tool in simplifying the staging protocol making further imaging studies unnecessary.

DESIGN

Retrospective, single center study.

PATIENTS AND SETTINGS

Seventy-five patients with rectal carcinoma were included and were divided into two groups according to their T score and nodal involvement status, as diagnosed by TRUS. Group 1 (n = 15) "local disease" (T1/T2 N0) and group 2 (n = 60) "locally advanced disease" are both eligible for neoadjuvant treatment (N/any T or T3/any N). For each patient, three CT imaging parameters that represent locally advanced disease, i.e., perirectal fat infiltration, local lymphadenopathy, and rectal wall thickening, were evaluated and compared between the two groups.

MAIN OUTCOME MEASURE

The capability of CT imaging to accurately predict locally advanced rectal carcinoma.

RESULTS

Rectal wall thickening on CT was found to have 92% PPV and perirectal lymphadenopathy 96% PPV for predicting a locally advanced stage. A combination of those two parameters results in a predictive PPV of 98%.

LIMITATIONS

This was a single center retrospective study, with a relatively small cohort.

CONCLUSIONS

CT is a valuable tool in the assessment and management of rectal carcinoma as it can identify locally advanced rectal cancer. This enables treatment without any further unnecessary evaluation.

Co-registered photoacoustic and ultrasound imaging of human colorectal cancer

<p>Colorectal cancer is the second most common malignancy diagnosed globally. Critical gaps exist in diagnostic and surveillance imaging modalities for colorectal neoplasia. Although prior studies have demonstrated the capability of photoacoustic imaging techniques to differentiate normal from neoplastic tissue in the gastrointestinal tract, evaluation of deep tissue with a fast speed and a large field of view remains limited. To investigate the ability of photoacoustic technology to image deeper tissue, we conducted a pilot study using a real-time co-registered photoacoustic tomography (PAT) and ultrasound (US) system. A total of 23 <italic>ex vivo</italic> human colorectal tissue samples were imaged immediately after surgical resection. Co-registered photoacoustic images of malignancies showed significantly increased PAT signal compared to normal regions of the same sample. The quantitative relative total hemoglobin (rHbT) concentration computed from four optical wavelengths, the spectral features, such as the mean spectral slope, and 0.5-MHz intercept extracted from PAT and US spectral data, and image features, such as the first- and second-order statistics along with the standard deviation of the mean radon transform of PAT images, have shown statistical significance between untreated colorectal tumors and the normal tissue. Using either a logistic regression model or a support vector machine, the best set of parameters of rHbT and PAT intercept has achieved area-under-the-curve (AUC) values of 0.97 and 0.95 for both training and testing data sets, respectively, for prediction of histologically confirmed invasive carcinoma.</p>.

Co-registered photoacoustic and ultrasound imaging of human colorectal cancer

<p>Colorectal cancer is the second most common malignancy diagnosed globally. Critical gaps exist in diagnostic and surveillance imaging modalities for colorectal neoplasia. Although prior studies have demonstrated the capability of photoacoustic imaging techniques to differentiate normal from neoplastic tissue in the gastrointestinal tract, evaluation of deep tissue with a fast speed and a large field of view remains limited. To investigate the ability of photoacoustic technology to image deeper tissue, we conducted a pilot study using a real-time co-registered photoacoustic tomography (PAT) and ultrasound (US) system. A total of 23 <italic>ex vivo</italic> human colorectal tissue samples were imaged immediately after surgical resection. Co-registered photoacoustic images of malignancies showed significantly increased PAT signal compared to normal regions of the same sample. The quantitative relative total hemoglobin (rHbT) concentration computed from four optical wavelengths, the spectral features, such as the mean spectral slope, and 0.5-MHz intercept extracted from PAT and US spectral data, and image features, such as the first- and second-order statistics along with the standard deviation of the mean radon transform of PAT images, have shown statistical significance between untreated colorectal tumors and the normal tissue. Using either a logistic regression model or a support vector machine, the best set of parameters of rHbT and PAT intercept has achieved area-under-the-curve (AUC) values of 0.97 and 0.95 for both training and testing data sets, respectively, for prediction of histologically confirmed invasive carcinoma.</p>.

Optimized light delivery probe using ball lenses for co-registered photoacoustic and ultrasound endo-cavity subsurface imaging

An optimized hand-held photoacoustic and ultrasound probe suitable for endo-cavity tumor subsurface imaging was designed and evaluated. Compared to previous designs, the prototype probe, consisting of four 1 mm multi-mode optical fibers attached with 1.5 mm diameter ball-shaped fiber tips sandwiched between a transvaginal ultrasound transducer and a custom-made sheath, demonstrated a higher light output and better beam homogeneity on tissue subsurface. The output power and fluence profile were simulated for different design parameters. A camera recorded fluence profiles through calibrated intralipid solution at various imaging depths. The light delivery efficiency was experimentally compared with and without the ball lenses, based on ex-vivo imaging of human colorectal cancer and in-vivo imaging of a palmar vein proximal to the human wrist. The simulations and experiments demonstrated that ball-shaped fiber tip design can achieve homogeneous fluence distribution on tissue subsurface with acceptable light output efficiency, suggesting its clinical potential for in-vivo endo-cavity imaging.

Clinical Utility of Positron Emission Tomography Magnetic Resonance Imaging (PET-MRI) in Gastrointestinal Cancers

Anatomic imaging utilizing both CT (computed tomography) and MRI (magnetic resonance imaging) limits the assessment of cancer metastases in lymph nodes and distant organs while functional imaging like PET (positron emission tomography) scan has its limitation in spatial resolution capacity. Hybrid imaging utilizing PET-CT and PET-MRI are novel imaging modalities that are changing the current landscape in cancer diagnosis, staging, and treatment response. MRI has shown to have higher sensitivity in soft tissue, head and neck pathology, and pelvic disease, as well as, detecting small metastases in the liver and bone compared to CT. Combining MRI with PET allows for detection of metastases that may have been missed with current imaging modalities. In this review, we will examine the clinical utility of FDG PET-MRI in the diagnosis and staging of gastrointestinal cancers with focus on esophageal, stomach, colorectal, and pancreatic cancers. We will also explore its role in treatment response and future directions associated with it.

An observational study of extending FOLFOX chemotherapy, lengthening the interval between radiotherapy and surgery, and enhancing pathological complete response rates in rectal cancer patients following preoperative chemoradiotherapy

INTRODUCTION

Patients with rectal cancer who exhibit a pathologic complete response to preoperative concurrent chemoradiotherapy have excellent oncologic outcomes. In this study, we evaluated the potential advantages of adding oxaliplatin to preoperative fluoropyrimidine-based chemoradiotherapy administered in rectal cancer patients.

METHODS

A total of 78 patients with rectal cancer were enrolled. Patients were administered chemoradiotherapy, which comprised radiotherapy and chemotherapy involving a 5-fluorouracil, leucovorin, and oxaliplatin regimen every 2 weeks. Surgery was performed 10-12 weeks after radiotherapy completion. Tumor regression, adverse events, surgical complications, and short-term clinical outcomes were recorded.

RESULTS

Two patients were excluded because of incomplete radiotherapy treatment or refusal of surgery. Eventually, 76 patients underwent total mesorectal excision and no perioperative mortality was observed. Of these, 20 patients (25.6%) developed grade 3 or 4 toxicity during concurrent chemoradiotherapy. Among the 76 patients who underwent surgery, 24 (31.6%) patients achieved a pathologic complete response. The sphincter preservation rate was 96.1% (73/76) in all patients and 92.2% (39/42) in patients with tumors located less than 5 cm from the anal verge. The 2-year overall and disease-free survivals were 94% and 87.4%, respectively.

CONCLUSION

The intensified multimodality therapy was well tolerated in our cohort and resulted in a considerably high pathologic complete response rate. Regardless of favorable short-term clinical outcomes, long-term oncologic outcomes will be closely monitored among the patients with a pathologic complete response.

Rectal cancer staging: Multidetector-row computed tomography diagnostic accuracy in assessment of mesorectal fascia invasion

AIM

To assess the diagnostic accuracy of multidetector-row computed tomography (MDCT) as compared with conventional magnetic resonance imaging (MRI), in identifying mesorectal fascia (MRF) invasion in rectal cancer patients.

METHODS

Ninety-one patients with biopsy proven rectal adenocarcinoma referred for thoracic and abdominal CT staging were enrolled in this study. The contrast-enhanced MDCT scans were performed on a 256 row scanner (ICT, Philips) with the following acquisition parameters: tube voltage 120 KV, tube current 150-300 mAs. Imaging data were reviewed as axial and as multiplanar reconstructions (MPRs) images along the rectal tumor axis. MRI study, performed on 1.5 T with dedicated phased array multicoil, included multiplanar T2 and axial T1 sequences and diffusion weighted images (DWI). Axial and MPR CT images independently were compared to MRI and MRF involvement was determined. Diagnostic accuracy of both modalities was compared and statistically analyzed.

RESULTS

According to MRI, the MRF was involved in 51 patients and not involved in 40 patients. DWI allowed to recognize the tumor as a focal mass with high signal intensity on high b-value images, compared with the signal of the normal adjacent rectal wall or with the lower tissue signal intensity background. The number of patients correctly staged by the native axial CT images was 71 out of 91 (41 with involved MRF; 30 with not involved MRF), while by using the MPR 80 patients were correctly staged (45 with involved MRF; 35 with not involved MRF). Local tumor staging suggested by MDCT agreed with those of MRI, obtaining for CT axial images sensitivity and specificity of 80.4% and 75%, positive predictive value (PPV) 80.4%, negative predictive value (NPV) 75% and accuracy 78%; while performing MPR the sensitivity and specificity increased to 88% and 87.5%, PPV was 90%, NPV 85.36% and accuracy 88%. MPR images showed higher diagnostic accuracy, in terms of MRF involvement, than native axial images, as compared to the reference magnetic resonance images. The difference in accuracy was statistically significant (P = 0.02).

CONCLUSION

New generation CT scanner, using high resolution MPR images, represents a reliable diagnostic tool in assessment of loco-regional and whole body staging of advanced rectal cancer, especially in patients with MRI contraindications.