Gadofosveset-enhanced MRI for the assessment of rectal cancer lymph nodes: predictive criteria

The Avocado Sign: A novel imaging marker for nodal staging in rectal cancer

OBJECTIVES

To evaluate the diagnostic performance of the Avocado Sign, a novel contrast-enhancement-based MR imaging marker, for prognostication of mesorectal lymph node spread in rectal cancer.

METHODS

This retrospective study included 106 patients with rectal cancer who underwent MRI examination. The Avocado Sign, defined as a hypointense core within an otherwise homogeneously hyperintense lymph node on contrast-enhanced T1-weighted images, was assessed. Of the cohort, 77 patients received neoadjuvant chemoradiotherapy followed by restaging MRI. Histopathological examination served as the reference standard. Diagnostic metrics were calculated and compared between subgroups using chi-square tests. Interobserver agreement was evaluated using Cohen's kappa.

RESULTS

The Avocado Sign demonstrated high diagnostic accuracy for predicting lymph node involvement, with an overall sensitivity of 88.7%, specificity of 84.9%, PPV of 85.5%, NPV of 88.2%, and accuracy of 86.8%. The area under the ROC curve was 0.87. Subgroup analysis revealed excellent performance in both patients undergoing surgery alone (sensitivity 100%, specificity 83.3%) and those receiving neoadjuvant therapy (sensitivity 84.2%, specificity 85.4%). Interobserver agreement was almost perfect (κ = 0.92).

CONCLUSION

The Avocado Sign is a promising imaging predictor for mesorectal lymph node status in rectal cancer. Its straightforward application, high reproducibility, and remarkable diagnostic accuracy underline its potential to refine MRI staging. However, further validation in larger, prospective multicenter studies is warranted to confirm these findings and assess their impact on clinical decision-making.

KEY POINTS

Question Can the Avocado Sign on contrast-enhanced MRI improve mesorectal lymph node staging in rectal cancer independently of classical morphological criteria? Findings The Avocado Sign demonstrated high sensitivity (88.7%) and specificity (84.9%) as a standalone marker for predicting mesorectal lymph node involvement. Clinical relevance Incorporating contrast-enhanced sequences and the Avocado Sign into MRI protocols enhances nodal staging accuracy in rectal cancer, potentially informing treatment decisions. Further validation is required to confirm its effectiveness and compare it with existing criteria.

MRI radiomics signature to predict lymph node metastasis after neoadjuvant chemoradiation therapy in locally advanced rectal cancer

PURPOSE

To investigative the performance of MRI-radiomics analysis derived from T2WI and apparent diffusion coefficients (ADC) images before and after neoadjuvant chemoradiation therapy (nCRT) separately or simultaneously for predicting post-nCRT lymph node status in patients with locally advanced rectal cancer (LARC). MATERIALS AND METHODS: Eighty-three patients (training cohort, n = 57; validation cohort, n = 26) with LARC between June 2017 and December 2022 were retrospectively enrolled. All the radiomics features were extracted from volume of interest on T2WI and ADC images from baseline and post-nCRT MRI. Delta-radiomics features were defined as the difference between radiomics features before and after nCRT. Seven clinical-radiomics models were constructed by combining the most predictive radiomics signatures and clinical parameters selected from support vector machine. Receiver operating characteristic curve (ROC) was used to evaluate the performance of models. The optimum model-based LNM was applied to assess 5-years disease-free survival (DFS) using Kaplan-Meier analysis. The end point was clinical or radiological locoregional recurrence or distant metastasis during postoperative follow-up.

RESULTS

Clinical-deltaADC radiomics combined model presented good performance for predicting post-CRT LNM in the training (AUC = 0.895,95%CI:0.838-0.953) and validation cohort (AUC = 0.900,95%CI:0.771-1.000). Clinical-deltaADC radiomics-postT2WI radiomics combined model also showed good performances (AUC = 0.913,95%CI:0.838-0.953) in the training and (AUC = 0.912,95%CI:0.771-1.000) validation cohort. As for subgroup analysis, clinical-deltaADC radiomics combined model showed good performance predicting LNM in ypT0-T2 (AUC = 0.827;95%CI:0.649-1.000) and ypT3-T4 stage (AUC = 0.934;95%CI:0.864-1.000). In ypT0-T2 stage, clinical-deltaADC radiomics combined model-based LNM could assess 5-years DFS (P = 0.030).

CONCLUSION

Clinical-deltaADC radiomics combined model could predict post-nCRT LNM, and this combined model-based LNM was associated with 5-years DFS in ypT0-T2 stage.

Technique to match mesorectal lymph nodes imaging findings to histopathology: node-by-node comparison

BACKGROUND

Lymph node status is critical for staging rectal cancer and determining neoadjuvant therapy regimens. Establishing a matching between imaging and histopathological lymph nodes is fundamental for predicting lymph node status. This study reports a technique to achieve node-by-node pairing of mesorectal lymph nodes between imaging findings and histopathology.

METHODS

Fifty-two patients with histopathologically verified rectal cancer underwent magnetic resonance imaging before surgery. The status of each lymph node in the surgical specimens was analyzed histopathologically and matched with preoperative imaging after the operation.

RESULTS

A total of 346 mesorectal lymph nodes were located on imaging evaluation, of which 313 were confirmed histopathologically, and 33 were unmatched. The total success rate of the technique was 90.5%. Node-by-node analysis revealed 280 benign and 33 malignant nodal structures.

CONCLUSION

The technique to match mesorectal lymph node imaging findings to histopathology was feasible and effective. It simplified the technical method and had a reasonable success matching rate, which could provide a standardized approach for obtaining a prospective correlation between imaging and histological findings, supporting all subsequent related studies at the level of mesorectal lymph nodes.

A magnetic resonance imaging (MRI)-based nomogram for predicting lymph node metastasis in rectal cancer: a node-for-node comparative study of MRI and histopathology

BACKGROUND

The aim of the present study was to investigate the potential risk factors for lymph node metastasis (LNM) in rectal cancer using magnetic resonance imaging (MRI), and to construct and validate a nomogram to predict its occurrence with node-for-node histopathological validation.

METHODS

Our prediction model was developed between March 2015 and August 2016 using a prospective primary cohort (32 patients, mean age: 57.3 years) that included 324 lymph nodes (LNs) from MR images with node-for-node histopathological validation. We evaluated multiple MRI variables, and a multivariable logistic regression analysis was used to develop the predictive nomogram. The performance of the nomogram was assessed with respect to its calibration, discrimination, and clinical usefulness. The performance of the nomogram in predicting LNM was validated in an independent clinical validation cohort comprising 182 consecutive patients.

RESULTS

The predictors included in the individualized prediction nomogram were chemical shift effect (CSE), nodal border, short-axis diameter of nodes, and minimum distance to rectal cancer or rectal wall. The nomogram showed good discrimination (C-index: 0.947; 95% confidence interval: 0.920-0.974) and good calibration in the primary cohort. Decision curve analysis confirmed the clinical usefulness of the nomogram in predicting the status of each LN. For the prediction of LN status in the clinical validation cohort by readers 1 and 2, the areas under the curves using the nomogram were 0.890 and 0.841, and the areas under the curves of readers using their experience were 0.754 and 0.704, respectively. Diagnostic efficiency was significantly improved by using the nomogram (P<0.001).

CONCLUSIONS

The nomogram, which incorporates CSE, nodal location, short-axis diameter, and minimum distance to rectal cancer or rectal wall, can be conveniently applied in clinical practice to facilitate the prediction of LNM in patients with rectal cancer.

Local Staging of Colon Cancer: A Cross-Sectional Analysis for Diagnostic Performance of Magnetic Resonance Imaging and by Experience

Preoperative magnetic resonance imaging was analyzed by four radiologists regarding local tumor staging (T and N) and the presence of extramural vascular involvement. An astonishingly high sensitivity for the detection of T 3/4 tumors (κ (quadratic weighted statistics constant) = 0.67), with considerably lower sensitivity for T 3 cd/4 tumors (κ = 0.51), high sensitivity for serosal involvement 76-87% (κ = 0.65) and extramural vascular involvement (87-98%, κ = 0.56). Sensitivity and specificity for lymph node involvement is lower (κ = 0.57). Magnetic resonance imaging with adequate experience can accurately detect tumors with invasion through the bowel wall and their prognostic factors.

Prediction Model Combining Clinical and MR Data for Diagnosis of Lymph Node Metastasis in Patients With Rectal Cancer

BACKGROUND

Determining the status of lymph node (LN) metastasis in rectal cancer patients preoperatively is crucial for the treatment option. However, the diagnostic accuracy of current imaging methods is low.

PURPOSE

To develop and test a model for predicting metastatic LNs of rectal cancer patients based on clinical data and MR images to improve the diagnosis of metastatic LNs.

STUDY TYPE

Retrospective.

SUBJECTS

In all, 341 patients with histologically confirmed rectal cancer were divided into one training set (120 cases) and three validation sets (69, 103, 49 cases).

FIELD STRENGTH/SEQUENCE

3.0T, axial and sagittal T₂ -weighted turbo spin echo and diffusion-weighted imaging (b = 0 s/mm² , 800 s/mm² ) ASSESSMENT: In the training dataset, univariate logistic regression was used to identify the clinical factors (age, gender, and tumor markers) and MR data that correlated with LN metastasis. Then we developed a prediction model with these factors by multiple logistic regression analysis. The accuracy of the model was verified using three validation sets and compared with the traditional MRI method.

STATISTICAL TESTS

Univariate and multivariate logistic regression. The area under the curve (AUC) value was used to quantify the diagnostic accuracy of the model.

RESULTS

Eight factors (CEA, CA199, ADCmean, mriT stage, mriN stage, CRM, EMVI, and differentiation degree) were significantly associated with LN metastasis in rectal cancer patients (P<0.1). In the training set (120) and the three validation sets (69, 103, 49), the AUC values of the model were much higher than the diagnosis by MR alone (training set, 0.902 vs. 0.580; first validation set, 0.789 vs. 0.743; second validation set, 0.774 vs. 0.573; third validation set, 0.761 vs. 0.524).

DATA CONCLUSION

For the diagnosis of metastatic LNs in rectal cancer patients, our proposed logistic regression model, combining clinical and MR data, demonstrated higher diagnostic efficiency than MRI alone.

LEVEL OF EVIDENCE

4 TECHNICAL EFFICACY STAGE: 2.

MRI morphologic and clinicopathologic characteristics for predicting outcomes in patients with locally advanced rectal cancer

PURPOSE

The aim of this study was to investigate the value of MRI morphologic and clinicopathologic factors for predicting 3-year disease-free survival (DFS) in patients with locally advanced rectal cancer (LARC).

METHOD

In this retrospective study, pre- and post-neoadjuvant chemoradiotherapy (nCRT) MRI morphologic (e.g., pre-nCRT MRI-detected extramural venous invasion) and clinicopathologic variabilities (e.g., pathological complete response) were evaluated in all patients. Three-year DFS was estimated using Kaplan-Meier product-limit method, and Cox proportional hazards models were used to determine associations between morphologic or clinicopathologic variabilities and survival outcomes.

RESULTS

A total of 115 patients (39 females and 76 males; median age, 54 years; age range, 28-82 years) with LARC treated with nCRT were enrolled. With a median follow-up of 48.0 months, the 3-year DFS was 79.0% for all patients. During follow-up, 18 patients died, 28 patients experienced relapse (26 distant, one local, and one both), and 69 patients were censored. MRI-detected extramural venous invasion (mrEMVI) was the only significantly independent factor of long-term survival, while HR was 2.308 (95% CI 1.151-4.629, P = 0.018) on univariate and 2.495 (95% CI 1.243-5.012, P = 0.010) on multivariate analysis. The 3-year cumulative survival rate in patients with mrEMVI negativity compared with positivity were 86.6% versus 65.0% (P = 0.015), respectively.

CONCLUSION

In conclusion, pre-nCRT mrEMVI status was the independent significant risk factor for long-term outcomes in LARC patients treated with nCRT, while the other morphologic and clinicopathologic characteristics were not related to the patient survival.

Lymph node metastasis in rectal cancer: comparison of MDCT and MR imaging for diagnostic accuracy

PURPOSE

To compare the diagnostic accuracies of MDCT and high-resolution MRI (HR-MRI) for regional nodal metastases with different short-axis diameter ranges in rectal cancer patients.

METHODS

Rectal adenocarcinoma patients who underwent both MDCT and HR-MRI before surgery were included. The maximum short-axis diameters of the nodes were measured, and were classified as benign or malignant on imaging findings. All of the nodes were subdivided as follows: ≤ 5 mm (Group A), > 5 mm and ≤ 10 mm (Group B) , and > 10 mm (Group C). The postoperative pathological reports were used as the standard, and the sensitivity, specificity, accuracy, ROC curve, and AUC value were calculated for each subgroup.

RESULTS

A total of 592 nodes were included in the node-to-node evaluation. In Group A, the specificity and accuracy of HR-MRI were significantly higher than those of MDCT (99.28% vs. 93.99%, P < 0.001; 95.78% vs. 89.56%, P = 0.010; respectively). In Group B, the specificity and accuracy of HR-MRI were also higher than those of MDCT (98.36% vs. 55.74%, P < 0.001; 80.45% vs. 66.17%, P < 0.001; respectively). For Groups A and B, the AUCs of MDCT were both 0.65, whereas those of HR-MRI were 0.76 and 0.82, respectively. In Group C, all nine malignant nodes were correctly diagnosed metastases on MDCT, whereas one was misjudged as benign on HR-MRI.

CONCLUSIONS

The diagnostic value of HR-MRI is superior to that of MDCT, with higher specificity, accuracy, and AUC values for HR-MRI than for MDCT.

Heterogeneous Enhancement Pattern in DCE-MRI Reveals the Morphology of Normal Lymph Nodes: An Experimental Study

Purpose

To investigate the heterogeneous enhancement pattern in normal lymph nodes of healthy mice by different albumin-binding contrast agents.

Methods

The enhancement of normal lymph nodes was assessed in mice by dynamic contrast-enhanced MRI (DCE-MRI) after the administration of two contrast agents characterized by different albumin-binding properties: gadopentetate dimeglumine (Gd-DTPA) and gadobenate dimeglumine (Gd-BOPTA). To take into account potential heterogeneities of the contrast uptake in the lymph nodes, k-means cluster analysis was performed on DCE-MRI data. Cluster spatial distribution was visually assessed. Statistical comparison among clusters and contrast agents was performed on semiquantitative parameters (AUC, wash-in rate, and wash-out rate) and on the relative size of the segmented clusters.

Results

Cluster analysis of DCE-MRI data revealed at least two main clusters, localized in the outer portion and in the inner portion of each lymph node. With both contrast agents, AUC (p < 0.01) and wash-in (p < 0.05) rates were greater in the inner cluster, which also showed a steeper wash-out rate than the outer cluster (Gd-BOPTA, p < 0.01; Gd-DTPA, p=0.056). The size of the outer cluster was greater than that of the inner cluster by Gd-DTPA (p < 0.05) and Gd-BOPTA (p < 0.01). The enhancement pattern of Gd-DTPA was not significantly different from the enhancement pattern of Gd-BOPTA.

Conclusion

DCE-MRI in normal lymph nodes shows a characteristic heterogeneous pattern, discriminating the periphery and the central portion of the lymph nodes. Such a pattern deserves to be investigated as a diagnostic marker for lymph node staging.

MRI of Rectal Cancer: Tumor Staging, Imaging Techniques, and Management

Rectal cancer is prone to local recurrence and systemic metastasis. However, owing to improvements in TNM staging and treatment, including a more widespread use of rectal MRI and increased radiologist awareness of the key rectal cancer TNM staging features, the mortality rate of rectal cancer has been declining over the past few decades in adults over 50 years of age. Currently, rectal MRI plays a key role in the pre- and posttreatment evaluation of rectal cancer, assisting the multidisciplinary team in tailoring the most appropriate treatment option. The benefits achieved with rectal MRI are strictly dependent on obtaining good-quality images, which is important for the characterization of the main anatomic structures and their relationship with the tumor. In primary staging, rectal MRI helps the radiologist (a) describe the tumor location and morphology, (b) provide its T and N categories, (c) detect the presence of extramural vascular invasion, and (d) identify its relationship with surrounding structures, including the sphincter complex and involvement of the mesorectal fascia. These features help diagnose locally advanced rectal tumors (categories T3c-d, T4, N1, and N2), for which neoadjuvant chemoradiotherapy (CRT) is indicated. In restaging after neoadjuvant CRT, in addition to reassessing the features noted during primary staging, rectal MRI can help in the assessment of treatment response, especially with the emergence of nonsurgical approaches such as "watch and wait." ^©RSNA, 2019.

Fat-suppressed gadolinium-enhanced isotropic high-resolution 3D-GRE-T1WI for predicting small node metastases in patients with rectal cancer

Background

To investigate the application value of fat-suppressed gadolinium-enhanced isotropic high-resolution 3D-GRE-T1WI in regional nodes with different short-axis diameter ranges in rectal cancer, especially in nodes ≤5 mm.

Methods

Patients with rectal adenocarcinoma confirmed by postoperative histopathology were included, and all the patients underwent preoperative 3.0 T rectal magnetic resonance imaging (MRI) and total mesorectal excision (TME) within 2 weeks after an MR scan. The harvested nodes from specimens were matched with nodes in the field of view (FOV) of images for a node-by-node evaluation. The maximum short-axis diameters of all the visible nodes in the FOV of images were measured by a radiologist; the morphological and enhancement characteristics of these nodes were also independently evaluated by two radiologists. The χ² test was used to evaluate differences in morphological and enhancement characteristics between benign and malignant nodes. The enhancement characteristics were further compared between benign and malignant nodes with different short-axis diameter ranges using the χ² test. Kappa statistics were used to describe interobserver agreement.

Results

A total of 441 nodes from 70 enrolled patients were included in the evaluation, of which 111 nodes were metastatic. Approximately 85.5 and 95.6% of benign nodes were found to have obvious enhancement and homogeneous or mild-heterogeneous enhancement, respectively, whereas approximately 89.2 and 85.1% of malignant nodes showed moderate or mild enhancement and obvious-heterogeneous or rim-like enhancement, respectively. The area under the receiver operating characteristic (ROC) curve (AUC) values of the enhancement degree for identifying the overall nodal status, nodes ≤5 mm and nodes > 5 mm and ≤ 10 mm were 0.887, 0.859 and 0.766 for radiologist 1 and 0.892, 0.823 and 0.774 for radiologist 2, respectively. The AUCs of enhancement homogeneity were 0.940, 0.928 and 0.864 for radiologist 1 and 0.944, 0.938 and 0.842 for radiologist 2, respectively. Nodal border and signal homogeneity were also of certain value in distinguishing metastatic nodes.

Conclusions

Enhancement characteristics based on fat-suppressed gadolinium-enhanced isotropic high-resolution 3D-GRE-T1WI were helpful for diagnosing metastatic nodes in rectal cancer and were a reliable indicator for nodes ≤5 mm.

Advanced Imaging Techniques in Evaluation of Colorectal Cancer

Imaging techniques are clinical decision-making tools in the evaluation of patients with colorectal cancer (CRC). The aim of this article is to discuss the potential of recent advances in imaging for diagnosis, prognosis, therapy planning, and assessment of response to treatment of CRC. Recent developments and new clinical applications of conventional imaging techniques such as virtual colonoscopy, dual-energy spectral computed tomography, elastography, advanced computing techniques (including volumetric rendering techniques and machine learning), magnetic resonance (MR) imaging-based magnetization transfer, and new liver imaging techniques, which may offer additional clinical information in patients with CRC, are summarized. In addition, the clinical value of functional and molecular imaging techniques such as diffusion-weighted MR imaging, dynamic contrast material-enhanced imaging, blood oxygen level-dependent imaging, lymphography with contrast agents, positron emission tomography with different radiotracers, and MR spectroscopy is reviewed, and the advantages and disadvantages of these modalities are evaluated. Finally, the future role of imaging-based analysis of tumor heterogeneity and multiparametric imaging, the development of radiomics and radiogenomics, and future challenges for imaging of patients with CRC are discussed. Online supplemental material is available for this article. ^©RSNA, 2018.

Magnetic resonance imaging of rectal cancer

Magnetic resonance imaging (MRI) is still the most commonly used imaging technique for the diagnosis of rectal cancer with the highest degree of accuracy, and it is also recommended by the National Comprehensive Cancer Network, European Society for Medical Oncology, and Chinese guidelines for diagnosis and treatment of colorectal cancer. The application of diffusion weighted imaging, apparent diffusion coefficient, diffusion weighted imaging with background signal suppression, intravoxel incoherent motion, perfusion imaging, magnetic resonance spectroscopy, and molecular imaging has provided many choices for tumor detection and preoperative staging, differential diagnosis of benign and malignant rectum lesions, postoperative follow-up, recurrence monitoring, and efficacy evaluation. We believe that with the development of basic theory and related technology, MRI for rectal cancer assessment will become more efficient.

Relative value of three whole-body MR approaches for PET-MR, including gadofosveset-enhanced MR, in comparison to PET-CT

PURPOSE

Evaluate MR protocol for PET-MR including coronal DWI (cDWI), fat-suppressed T2 (T2w), and gadofosveset-enhanced T1 (CE).

MATERIALS AND METHODS

18 patients underwent same-day PET-CT and PET-MR. Image quality and performance of each sequence, and combination of all three sequences, was evaluated with respect to PET-CT.

RESULTS

Lesion conspicuity was best on cDWI, while delineation was best on CE. Considering all three sequences combined, both readers showed good sensitivity and specificity (>80%). Relative sensitivity was highest on CE and lowest on T2w.

CONCLUSIONS

Whole-body MR performed well in detecting malignant lesions compared to PET-CT. CE showed overall highest performance.

Added value of dedicated axillary hybrid 18F-FDG PET/MRI for improved axillary nodal staging in clinically node-positive breast cancer patients: a feasibility study

Purpose

To investigate the feasibility and potential added value of dedicated axillary 18F-FDG hybrid PET/MRI, compared to standard imaging modalities (i.e. ultrasound [US], MRI and PET/CT), for axillary nodal staging in clinically node-positive breast cancer.

Methods

Twelve patients with clinically node-positive breast cancer underwent axillary US and dedicated axillary hybrid 18F-FDG PET/MRI. Nine of the 12 patients also underwent whole-body PET/CT. Maximum standardized uptake values (SUVmax) were measured for the primary breast tumor and the most FDG-avid axillary lymph node. A positive axillary lymph node on dedicated axillary hybrid PET/MRI was defined as a moderate to very intense FDG-avid lymph node. The diagnostic performance of dedicated axillary hybrid PET/MRI was calculated by comparing quantitative and its qualitative measurements to results of axillary US, MRI and PET/CT. The number of suspicious axillary lymph nodes was subdivided as follows: N0 (0 nodes), N1 (1–3 nodes), N2 (4–9 nodes) and N3 (≥ 10 nodes).

Results

According to dedicated axillary hybrid PET/MRI findings, seven patients were diagnosed with N1, four with N2 and one with N3. With regard to mean SUVmax, there was no significant difference in the primary tumor (9.0 [±5.0] vs. 8.6 [±5.7], p = 0.678) or the most FDG-avid axillary lymph node (7.8 [±5.3] vs. 7.7 [±4.3], p = 0.767) between dedicated axillary PET/MRI and PET/CT. Compared to standard imaging modalities, dedicated axillary hybrid PET/MRI resulted in changes in nodal status as follows: 40% compared to US, 75% compared to T2-weighted MRI, 40% compared to contrast-enhanced MRI, and 22% compared to PET/CT.

Conclusions

Adding dedicated axillary 18F-FDG hybrid PET/MRI to diagnostic work-up may improve the diagnostic performance of axillary nodal staging in clinically node-positive breast cancer patients.

MRI for Local Staging of Colon Cancer: Can MRI Become the Optimal Staging Modality for Patients With Colon Cancer?

BACKGROUND

Colon cancer is currently staged with CT. However, MRI is superior in the detection of colorectal liver metastasis, and MRI is standard in local staging of rectal cancer. Optimal (local) staging of colon cancer could become crucial in selecting patients for neoadjuvant treatment in the near future (Fluoropyrimidine Oxaliplatin and Targeted Receptor Preoperative Therapy trial).

OBJECTIVE

The purpose of this study was to evaluate the diagnostic performance of MRI for local staging of colon cancer.

DESIGN

This was a retrospective study.

SETTINGS

The study was conducted at the Maastricht University Medical Centre.

PATIENTS

In total, 55 patients with biopsy-proven colon carcinoma were included.

MAIN OUTCOME MEASURES

All of the patients underwent an MRI (1.5-tesla; T2 and diffusion-weighted imaging) of the abdomen and were retrospectively analyzed by 2 blinded, independent readers. Histopathology after resection was the reference standard. Both readers evaluated tumor characteristics, including invasion through bowel wall (T3/T4 tumors), invasion beyond bowel wall of ≥5 mm and/or invasion of surrounding organs (T3cd/T4), serosal involvement, extramural vascular invasion, and malignant lymph nodes (N+). Interobserver agreement was compared using κ statistics.

RESULTS

MRI had a high sensitivity (72%-91%) and specificity (84%-89%) in detecting T3/T4 tumors (35/55) and a low sensitivity (43%-67%) and high specificity (75%-88%) in detecting T3cd/T4 tumors (15/55). For detecting serosal involvement and extramural vascular invasion, MRI had a high sensitivity and moderate specificity, as well as a moderate sensitivity and specificity in the detection of nodal involvement. Interobserver agreements were predominantly good; the more experienced reader achieved better results in the majority of these categories.

LIMITATIONS

The study was limited by its retrospective nature and moderate number of inclusions.

CONCLUSIONS

MRI has a good sensitivity for tumor invasion through the bowel wall, extramural vascular invasion, and serosal involvement. In addition, together with its superior liver imaging, MRI might become the optimal staging modality for colon cancer. However, more research is needed to confirm this. See Video Abstract at http://links.lww.com/DCR/A309.

Advanced imaging of colorectal cancer: From anatomy to molecular imaging

Imaging techniques play a key role in the management of patients with colorectal cancer. The introduction of new advanced anatomical, functional, and molecular imaging techniques may improve the assessment of diagnosis, prognosis, planning therapy, and assessment of response to treatment of these patients. Functional and molecular imaging techniques in clinical practice may allow the assessment of tumour-specific characteristics and tumour heterogeneity. This paper will review recent developments in imaging technologies and the evolving roles for these techniques in colorectal cancer.

TEACHING POINTS

• Imaging techniques play a key role in the management of patients with colorectal cancer. • Advanced imaging techniques improve the evaluation of these patients. • Functional and molecular imaging allows assessment of tumour hallmarks and tumour heterogeneity.

Role of Magnetic Resonance Imaging in Primary Rectal Cancer-Standard Protocol and Beyond

New-generation magnetic resonance imaging (MRI) scanners with optimal phased-array body coils have contributed to obtainment of high-resolution T2-weighted turbo spin echo images in which visualization of anatomical details such as the mesorectal fascia and the bowel wall layers is feasible. Preoperative, locoregional staging of rectal cancer with MRI, considered standard of care nowadays, relies on these images for stratification of high-risk patients for local recurrence, patients most likely to benefit from neoadjuvant therapy, as well as patients who exhibit imaging features indicative of a high risk of metastatic disease. Functional imaging, including optimized for rectal cancer diffusion-weighted imaging and more recently use of dynamic contrast-enhanced MRI, combined with radiologists׳ rising level of familiarity regarding the assessment of reactive changes postchemoradiation treatment, have shown to increase MRI staging accuracy after neoadjuvant treatment. Our intention is to review already established standard protocols for primary rectal cancer and go through potential additional promising imaging tools.

Clinical relevance of morphologic MRI criteria for the assessment of lymph nodes in patients with rectal cancer

AIM

The aim of this study is the evaluation of lymph node staging by magnetic resonance imaging (MRI) within clinical routine in patients with rectal cancer.

METHOD

Routine MRI reports (3 T) of 65 consecutive patients with rectal cancer were retrospectively categorized in lymph node tumor positive or negative (mriN+; mriN0) and compared to the final histopathological results (pN+; pN0). Sensitivity, specificity, negative predictive value (NPV), positive predictive value (PPV), and accuracy were calculated. The original MRI readings were then reanalyzed in order to identify the longest short-axis lymph node diameter for each patient. A receiver operating characteristic (ROC) curve was used to calculate a possible cutoff value for the short-axis lymph node diameter.

RESULTS

Overall sensitivity was 94 %, specificity 13 %, NPV 86 %, PPV 28 %, and accuracy 34 %. The best accuracy could be calculated for a short-diameter cutoff of ≤5 mm (83 %); pN+ and pN0 groups were then significantly different (p < 0.0001).

CONCLUSION

In clinical routine, lymph node assessment in patients with rectal cancer through MRI tends to overstage malignant lymphadenopathy. A ≤5-mm cutoff value for the short-axis lymph node diameter of benign nodes is able to improve the accuracy and has potential to lower the risk of overstaging.

Neoadjuvant chemoradiation therapy and pathological complete response in rectal cancer

The management of rectal cancer has evolved significantly in the last few decades. Significant improvements in local disease control were achieved in the 1990s, with the introduction of total mesorectal excision and neoadjuvant radiotherapy. Level 1 evidence has shown that, with neoadjuvant chemoradiation therapy (CRT) the rates of local recurrence can be lower than 6% and, as a result, neoadjuvant CRT currently represents the accepted standard of care. This approach has led to reliable tumor down-staging, with 15-27% patients with a pathological complete response (pCR)-defined as no residual cancer found on histological examination of the specimen. Patients who achieve pCR after CRT have better long-term outcomes, less risk of developing local or distal recurrence and improved survival. For all these reasons, sphincter-preserving procedures or organ-preserving options have been suggested, such as local excision of residual tumor or the omission of surgery altogether. Although local recurrence rate has been stable at 5-6% with this multidisciplinary management method, distal recurrence rates for locally-advanced rectal cancers remain in excess of 25% and represent the main cause of death in these patients. For this reason, more recent trials have been looking at the administration of full-dose systemic chemotherapy in the neoadjuvant setting (in order to offer early treatment of disseminated micrometastases, thus improving control of systemic disease) and selective use of radiotherapy only in non-responders or for low rectal tumors smaller than 5 cm.

Tumor-induced lymph node alterations detected by MRI lymphography using gadolinium nanoparticles

Contrast-enhanced MRI lymphography shows potential to identify alterations in lymph drainage through lymph nodes (LNs) in cancer and other diseases. MRI studies have typically used low molecular weight gadolinium contrast agents, however larger gadolinium-loaded nanoparticles possess characteristics that could improve the specificity and sensitivity of lymphography. The performance of three gadolinium contrast agents with different sizes and properties was compared by 3T MRI after subcutaneous injection. Mice bearing B16-F10 melanoma footpad tumors were imaged to assess tumor-induced alterations in lymph drainage through tumor-draining popliteal and inguinal LNs versus contralateral uninvolved drainage. Gadolinium lipid nanoparticles were able to identify tumor-induced alterations in contrast agent drainage into the popliteal LN, while lower molecular weight or albumin-binding gadolinium agents were less effective. All of the contrast agents distributed in foci around the cortex and medulla of tumor-draining popliteal LNs, while they were restricted to the cortex of non-draining LNs. Surprisingly, second-tier tumor-draining inguinal LNs exhibited reduced uptake, indicating that tumors can also divert LN drainage. These characteristics of tumor-induced lymph drainage could be useful for diagnosis of LN pathology in cancer and other diseases. The preferential uptake of nanoparticle contrasts into tumor-draining LNs could also allow selective targeting of therapies to tumor-draining LNs.

MRI of Rectal Cancer: An Overview and Update on Recent Advances

OBJECTIVE

MRI is the modality of choice for rectal cancer staging. The high soft-tissue contrast of MRI accurately assesses the extramural tumor spread and relation to mesorectal fascia and the sphincter complex. This article reviews the role of MRI in the staging and treatment of rectal cancer. The relevant anatomy, MRI techniques, preoperative staging, post-chemoradiation therapy (CRT) imaging, and tumor recurrence are discussed with special attention to recent advances in knowledge.

CONCLUSION

MRI is the modality of choice for staging rectal cancer to assist surgeons in obtaining negative surgical margins. MRI facilitates the accurate assessment of mesorectal fascia and the sphincter complex for surgical planning. Multiparametric MRI may also help in the prediction and estimation of response to treatment and in the detection of recurrent disease.

MR imaging probes: design and applications

This perspective outlines strategies towards the development of MR imaging probes that our lab has explored over the last 15 years. Namely, we discuss methods to enhance the signal generating capacity of MR probes and how to achieve tissue specificity through protein targeting or probe activation within the tissue microenvironment.

Magnetic resonance imaging and endorectal ultrasound for diagnosis of rectal lesions

Endorectal ultrasonography (ERUS) and magnetic resonance imaging (MRI) allow exploring the morphology of the rectum in detail. Use of such data, especially assessment of the rectal wall, is an important tool for ascertaining the perianal fistula localization as well as stage of the cancer and planning it appropriate treatment, as stage T3 tumors are usually treated with neoadjuvant therapy, whereas T2 tumors are initially managed surgically. The only advantage of ERUS over MRI is the possibility of assessing T1 tumors that could be treated by transanal endoscopic microsurgery. However, MRI is better for visualizing most radiological prognostic features in rectal or anal cancer such as a circumferential resection margin less than 1 mm, T stage at T1-T2 or T3 tumors with extramural extension less than 5 mm, absence of extramural vascular invasion, N stage at N0/N1, and tumors located in the middle or upper third of the rectum. It can also evaluate the intersphincteric space or levator ani muscle involvement. Increased signal on diffusion weighted imaging (DWI) and low apparent diffusion coefficient (ADC) values as well as an irregular contour and heterogeneous internal signal intensity seem to predict the involvement of pelvic lymphatic nodes better than their size alone. Computed tomography as well as other examination techniques, including digital rectal examination, contrast edema, recto- and colonoscopy, are less useful in staging of rectal cancer but still are very important screening tools.

Tumor-induced alterations in lymph node lymph drainage identified by contrast-enhanced MRI

BACKGROUND

To use high resolution MRI lymphography to characterize altered tumor-draining lymph node (TDLN) lymph drainage in response to growth of aggressive tumors.

METHODS

Six mice bearing B16-F10 melanomas in one rear footpad were imaged by 3.0 Tesla (T) MRI before and after subcutaneous injection of Gadofosveset trisodium (Gd-FVT) contrast agent into both rear feet. Gd-FVT uptake into the left and right draining popliteal LNs was quantified and compared using Wilcoxon signed-rank test. Fluorescent dextran lymphography compared patterns of LN lymph drainage with the pattern of immunostained lymphatic sinuses by fluorescence microscopy.

RESULTS

TDLNs exhibited greater Gd-FVT uptake than contralateral uninvolved LNs, although this difference did not reach significance (P < 0.06). Foci of contrast agent consistently surrounded the medulla and cortex of TDLNs, while Gd-FVT preferentially accumulated in the cortex of contralateral LNs at 5 and 15 min after injection. Fluorescent dextran lymphography confirmed these distinct contrast agent uptake patterns, which correlated with lymphatic sinus growth in TDLNs.

CONCLUSION

3.0T MRI lymphography using Gd-FVT identified several distinctive alterations in the uptake of contrast agent into TDLNs, which could be useful to identify the correct TDLN, and to characterize TDLN lymphatic sinus growth that may predict metastatic potential.

In silico evaluation of gadofosveset pharmacokinetics in different population groups using the Simcyp® simulator platform

Purpose

Gadofosveset is a Gd-based contrast agent used for magnetic resonance imaging (MRI). Gadolinium kinetic distribution models are implemented in T1-weighted dynamic contrast-enhanced perfusion MRI for characterization of lesion sites in the body. Physiology changes in a disease state potentially can influence the pharmacokinetics of drugs and to this respect modify the distribution properties of contrast agents. This work focuses on the in silico modelling of pharmacokinetic properties of gadofosveset in different population groups through the application of physiologically-based pharmacokinetic models (PBPK) embedded in Simcyp® population pharmacokinetics platform.

Methods

Physicochemical and pharmacokinetic properties of gadofosveset were introduced into Simcyp® simulator platform and a min-PBPK model was applied. In silico clinical trials were generated simulating the administration of the recommended dose for the contrast agent (i.v., 30 mg/kg) in population cohorts of healthy volunteers, obese, renal and liver impairment, and in a generated virtual oncology population. Results were evaluated regarding basic pharmacokinetic parameters of Cmax, AUC and systemic CL and differences were assessed through ANOVA and estimation of ratio of geometric mean between healthy volunteers and the other population groups.

Results

Simcyp® predicted a mean Cmax = 551.60 mg/l, a mean AUC = 4079.12 mg/L*h and a mean systemic CL = 0.56 L/h for the virtual population of healthy volunteers. Obese population showed a modulation in Cmax and CL, attributed to increased administered dose. In renal and liver impairment cohorts a significant modulation in Cmax, AUC and CL of gadofosveset is predicted. Oncology population exhibited statistical significant differences regarding AUC when compared with healthy volunteers.

Conclusions

This work employed Simcyp® population pharmacokinetics platform in order to compute gadofosveset’s pharmacokinetic profiles through PBPK models and in silico clinical trials and evaluate possible differences between population groups. The approach showed promising results that could provide new insights regarding administration of contrast agents in special population cohorts. In silico pharmacokinetics could further be used for evaluating of possible toxicity, interpretation of MRI PK image maps and development of novel contrast agents.

Value of gadofosveset-enhanced MRI and multiplanar reformatting for selecting good responders after chemoradiation for rectal cancer

OBJECTIVES

Our primary objective was to evaluate diagnostic performance of gadofosveset T1-weighted magnetic resonance imaging (T1W MRI) for discriminating between ypT0-2 and ypT3-4 tumours after chemoradiation therapy (CRT) for rectal cancer compared with T2W MRI for a general and expert reader. Second objectives included assessing the value of multiplanar reformatting (MPR) and interobserver agreement.

METHODS

A general and expert reader evaluated 49 patients for likelihood of ypT0-2 tumour after CRT on T2W, gadofosveset T1W MRI, and gadofosveset T1W MRI + T2W MRI. The general reader scored with and without MPR. Confidence level scores were used to construct receiver-operating characteristic (ROC) curves. Area under the curve (AUC) values and diagnostic parameters were calculated and compared.

RESULTS

Gadofosveset T1W MRI + T2W MRI showed slightly superior sensitivity than T2W MRI for the general but not the expert reader. Specificity was higher for the expert on gadofosveset T1W MRI only compared with T2W MRI only (100% vs. 82%). MPR did not increase diagnostic performance. Interobserver agreement was highest for the combination of gadofosveset-enhanced T1W imaging plus T2W MRI.

CONCLUSIONS

The sole use or addition of gadofosveset-enhanced T1W MRI to T2W MRI did not increase significantly diagnostic performance for assessing ypT0-2 tumours. Adding gadofosveset-enhanced T1W MRI slightly increased sensitivity for the general reader and specificity for the expert reader, but this increase was not significant for more accurate clinical decision making. MPR did not improve diagnostic performance.

KEY POINTS

• ycT restaging with MRI in rectal cancer is challenging. • Gadofosveset-enhanced T1W MRI has shown promise for nodal restaging. • Gadofosveset-enhanced T1W MRI did not significantly increase diagnostic performance for assessing ypT0-2-tumours. • Addition of the gadofosveset sequence to T2W MRI slightly increased sensitivity for the general reader. • MPR did not improve diagnostic performance of ycT staging.

Multiparametric MRI of rectal cancer in the assessment of response to therapy: a systematic review

BACKGROUND

Conventional MRI is limited in the assessment of nodal status and T status after neoadjuvant chemoradiotherapy. Multiparametric MRI strives to overcome these issues by directly measuring the local microcirculation and cellular environment, thus possibly allowing for a more reliable evaluation of response to therapy.

OBJECTIVE

We assessed the available literature for the value of multiparametric MRI sequences (diffusion-weighted and dynamic contrast-enhanced imaging) in determining the response to neoadjuvant chemoradiotherapy in patients with rectal cancer.

DATA SOURCES

We conducted a systematic literature research in the PubMed database.

STUDY SELECTION

English-language publications of the years 2000-2013 that applied multiparametric MRI in the neoadjuvant setting were included in this study.

INTERVENTION

Patients received neoadjuvant chemoradiotherapy and MRI examinations for staging and assessment of response.

MAIN OUTCOME MEASURES

Accuracy, specificity, and sensitivity of MRI in prediction/assessment of response to therapy were the included measures.

RESULTS

Forty-three studies were included in this review; 30 of them included diffusion-weighted imaging sequences, and 13 included dynamic contrast-enhanced MRI. Conventional MRI is limited in the accuracy of both T and N stages and response assessment. Diffusion-weighted imaging and dynamic contrast-enhanced MRIs showed additional value in both the prediction and detection of (complete) response to therapy compared with conventional sequences alone, as well as in correct N staging along with new experimental contrast agents.

LIMITATIONS

The lack of standardization represents an important technical limitation. Most studies are conducted in an experimental setting; therefore, larger multicenter prospective studies are needed to verify the present findings.

CONCLUSIONS

Advanced, functional MRI techniques allow for the quantification of tumor biological processes, such as microcirculation, vascular permeability, and tissue cellularity. This new technology has begun to show potential advantages over standard morphologic imaging in the restaging of rectal cancer, allowing for more accurate prognostication of response and potentially introducing an era allowing earlier treatment alteration and more accurate noninvasive surveillance, which could improve patient outcomes.

Multi-parametric MRI of rectal cancer - do quantitative functional MR measurements correlate with radiologic and pathologic tumor stages?

PURPOSE

The purpose of this study is two-fold. First, to evaluate, whether functional rectal MRI techniques can be analyzed in a reproducible manner by different readers and second, to assess whether different clinical and pathologic T and N stages can be differentiated by functional MRI measurements.

MATERIALS AND METHODS

54 patients (38 men, 16 female; mean age 63.2 ± 12.2 years) with pathologically proven rectal cancer were included in this retrospective IRB-approved study. All patients were referred for a multi-parametric MRI protocol on a 3 Tesla MR-system, consisting of a high-resolution, axial T2 TSE sequence, DWI and perfusion imaging (plasma flow -s PFTumor) prior to any treatment. Two experienced radiologists evaluated the MRI measurements, blinded to clinical data and outcome. Inter-reader correlation and the association of functional MRI parameters with c- and p-staging were analyzed.

RESULTS

The inter-reader correlation for lymph node (ρ 0.76-0.94; p<0.0002) and primary tumor (ρ 0.78-0.92; p<0.0001) apparent diffusion coefficient and plasma flow (PF) values was good to very good. PFTumor values decreased with cT stage with significant differences identified between cT2 and cT3 tumors (229 versus 107.6 ml/100ml/min; p=0.05). ADCTumor values did not differ significantly. No substantial discrepancies in lymph node ADCLn values or short axis diameter were found among cN1-3 stages, whereas PFLn values were distinct between cN1 versus cN2 stages (p=0.03). In the patients without neoadjuvant RCT no statistically significant differences in the assessed functional parameters on the basis of pathologic stage were found.

CONCLUSION

This study illustrates that ADC as well as MR perfusion values can be analyzed with good interobserver agreement in patients with rectal cancer. Moreover, MR perfusion parameters may allow accurate differentiation of tumor stages. Both findings suggest that functional MRI parameters may help to discriminate T and N stages for clinical decision making.

Performance of gadofosveset-enhanced MRI for staging rectal cancer nodes: can the initial promising results be reproduced?

OBJECTIVES

A previous study showed promising results for gadofosveset-trisodium as a lymph node magnetic resonance imaging (MRI) contrast agent in rectal cancer. The aim of this study was to prospectively confirm the diagnostic performance of gadofosveset MRI for nodal (re)staging in rectal cancer in a second patient cohort.

METHODS

Seventy-one rectal cancer patients were prospectively included, of whom 13 (group I) underwent a primary staging gadofosveset MRI (1.5-T) followed by surgery (± preoperative 5 × 5 Gy) and 58 (group II) underwent both primary staging and restaging gadofosveset MRI after a long course of chemoradiotherapy followed by surgery. Nodal status was scored as (y)cN0 or (y)cN+ by two independent readers (R1, R2) with different experience levels. Results were correlated with histology on a node-by-node basis.

RESULTS

Sensitivity, specificity and area under the receiver operating characteristics curve (AUC) were 94%, 79% and 0.89 for the more experienced R1 and 50%, 83% and 0.74 for the non-experienced R2. R2's performance improved considerably after a learning curve, to an AUC of 0.83. Misinterpretations mainly occurred in nodes located in the superior mesorectum, nodes located in between vessels and nodes containing micrometastases.

CONCLUSIONS

This prospective study confirms the good diagnostic performance of gadofosveset MRI for nodal (re)staging in rectal cancer.

KEY POINTS

• Gadofosveset-enhanced MRI shows high performance for nodal (re)staging in rectal cancer. • Gadofosveset MRI may facilitate better selection of patients for personalised treatment. • Results can be reproduced by non-expert readers. • Experience of 50-60 cases is required to achieve required expertise level. • Main pitfalls are nodes located between vessels and nodes containing micrometastases.

Rectal cancer staging: focus on the prognostic significance of the findings described by high-resolution magnetic resonance imaging

High-resolution (HR) magnetic resonance imaging (MRI) has become an indispensable tool for multidisciplinary teams (MDTs) addressing rectal cancer. It provides anatomic information for surgical planning and allows patients to be stratified into different groups according to the risk of local and distant recurrence. One of the objectives of the MDT is the preoperative identification of high-risk patients who will benefit from neoadjuvant treatment. For this reason, the correct evaluation of the circumferential resection margin (CRM), the depth of tumor spread beyond the muscularis propria, extramural vascular invasion and nodal status is of the utmost importance. Low rectal tumors represent a special challenge for the MDT, because decisions seek a balance between oncologic safety, in the pursuit of free resection margins, and the patient's quality of life, in order to preserve sphincter function. At present, the exchange of information between the different specialties involved in dealing with patients with rectal cancer can rank the contribution of colleagues, auditing their work and incorporating knowledge that will lead to a better understanding of the pathology. Thus, beyond the anatomic description of the images, the radiologist's role in the MDT makes it necessary to know the prognostic value of the findings that we describe, in terms of recurrence and survival, because these findings affect decision making and, therefore, the patients' life. In this review, the usefulness of HR MRI in the initial staging of rectal cancer and in the evaluation of neoadjuvant treatment, with a focus on the prognostic value of the findings, is described as well as the contribution of HR MRI in assessing patients with suspected or confirmed recurrence of rectal cancer.