Diffusion-weighted MR imaging of the rectum: clinical applications

Apparent diffusion coefficient derived from diffusion-weighted imaging to differentiate between tumor, tumor-adjacent and tumor-distant tissues in resectable rectal adenocarcinoma

PURPOSE

To evaluate feasibility of apparent diffusion coefficient (ADC) at different b-values to differentiate between tumor, tumor-adjacent and tumor-distant tissues in rectal adenocarcinoma (RA).

MATERIALS AND METHODS

Seventy consecutive patients with RA undergoing preoperative diffusion-weighted imaging were retrospectively enrolled. ADCs of tumor, proximal tumor-adjacent tissue (PTA) and tumor-distant tissue (PTD), and distal tumor-adjacent tissue (DTA) and tumor-distant tissue (DTD) were calculated with b-values of 0 and 800 sec/mm2, 0 and 1000 sec/mm2, 0 and 1500 sec/mm2, and multiple b-values of 0, 50, 100, 800, 1000 and 1500 sec/mm2. Statistical analysis was performed to determine feasibility of ADC to differentiate between pairwise tissues.

RESULTS

Mean ADC of tumor was lower than those of PTA, PTD, DTA and DTD; and mean ADCs of PTA and DTA were lower than those of PTD and DTD at all b-values, respectively (all P-values < 0.001). ADC cut-offs of 1.089 × 10-3 mm2/sec (b = 0, 1000 sec/mm2) or 1.215 × 10-3 mm2/sec (b = 0, 800 sec/mm2), and 1.142 × 10-3 mm2/sec (b = 0, 1000 sec/mm2) or 0.995 × 10-3 mm2/sec (b = 0, 1500 sec/mm2) achieved excellent performance in differentiating tumor from PTA or PTD, and tumor from DTA or DTD (area under receiver operating characteristic curves [AUCs]: 0.813 or 0.952, and 0.970 or 0.996), respectively. ADC cut-offs of 1.625 × 10-3 mm2/sec (b = 0, 800 sec/mm2), and 1.165 × 10-3 mm2/sec (b = 0, 1500 sec/mm2) could differentiate PTA from PTD, and DTA from DTD (AUCs: 0.709 and 0.673), respectively.

CONCLUSION

ADC can help differentiate between tumor, tumor-adjacent and tumor-distant tissues in RA.

FDG-PET/CT and MR imaging for target volume delineation in rectal cancer radiotherapy treatment planning: a systematic review

Aim:

The aim of this systematic review was to synthesise and summarise evidence surrounding the clinical use of fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography (FDG-PET/CT) and magnetic resonance imaging (MRI) for target volume delineation (TVD) in rectal cancer radiotherapy planning.

Methods:

PubMed, EMBASE, Cochrane library, CINAHL, Web of Science and Scopus databases and other sources were systematically queried using keywords and relevant synonyms. Eligible full-text studies were assessed for methodological quality using the QUADAS-2 tool.

Results:

Eight of the 1448 studies identified met the inclusion criteria. Findings showed that MRI significantly delineate larger tumour volumes (TVs) than FDG-PET/CT while diffusion-weighted magnetic resonance imaging (DW-MRI) defined smaller gross tumour volumes (GTVs) compared to T2 weighted-Magnetic Resonance Image. CT-based GTVs were found to be larger compared to FDG-PET/CT. FDG-PET/CT also identified new lesions in 15–17% patients and TVs extending outside the routinely used clinical standard CT TV in 29–83% patients. Between observers, delineated volumes were similar and consistent between MRI sequences, whereas interobserver agreement was significantly improved with FDG-PET/CT than CT.

Conclusion:

FDG-PET/CT and DW-MRI appear to delineate smaller rectal TVs and show improved interobserver variability. Overall, this study provides valuable insights into the amount of attention in the research literature that has been paid to imaging for TVD in rectal cancer.

Multiparametric MRI of rectal cancer-repeatability of quantitative data: a feasibility study

PURPOSE

In this study, we aimed to analyze the repeatability of quantitative multiparametric rectal magnetic resonance imaging (MRI) parameters with different measurement techniques.

METHODS

All examinations were performed with 3 T MRI system. In addition to routine sequences for rectal cancer imaging protocol, small field-of-view diffusion-weighted imaging and perfusion sequences were acquired in each patient. Apparent diffusion coefficient (ADC) was used for diffusion analysis and ktrans was used for perfusion analysis. Three different methods were used in measurement of these parameters; measurements were performed twice by one radiologist for intraobserver and separately by three radiologists for interobserver variability analysis. ADC was measured by the lowest value, the value at maximum wall thickness, and freehand techniques. Ktrans was measured at the slice with maximum wall thickness, by freehand drawn region of interest (ROI), and at the dark red spot with maximum value.

RESULTS

A total of 30 patients with biopsy-proven rectal adenocarcinoma were included in the study. The mean values of the parameters measured by the first radiologist on the first and second measurements were as follows: mean lowest ADC, 721.31±147.18 mm2/s and 718.96±135.71 mm2/s; mean ADC value on the slice with maximum wall thickness, 829.90±144.24 mm2/s and 829.48±149.23 mm2/s; mean ADC value measured by freehand ROI on the slice with maximum wall thickness, 846.56±136.31 mm2/s and 848.23±144.15 mm2/s; mean ktrans value on the slice with maximum wall thickness, 0.219±0.080 and 0.214±0.074; mean ktrans by freehand ROI technique (including as much tumoral tissue as possible), 0.208±0.074 and 0.207±0.069; mean ktrans measured from the dark red foci, 0.308±0.109 and 0.311±0.105. Intraobserver agreement was very good among diffusion and perfusion parameters obtained with all three measurement techniques. Interobserver agreement was very good, except for one of the measurement techniques. As far as interobserver variability is considered, only ADC value measured on the slice with maximum wall thickness differed significantly.

CONCLUSION

Multiparametric MRI of rectum, using ADC as the diffusion and ktrans as the perfusion parameter is a repeatable technique. This technique may potentially be used in prediction and evaluation of neoadjuvant treatment response. New studies with larger patient groups are needed to validate the role of multiparametric MRI.

Multiparametric MRI in rectal cancer

MRI has a pivotal role in both pretreatment staging and posttreatment evaluation of rectal cancer. The accuracy of MRI in pretreatment staging is higher compared with posttreatment evaluation. This occurs due to similar signal intensities of tumoral and posttreatment fibrotic, necrotic, and inflamed tissue. This limitation occurs with conventional MRI of the rectum with morphologic sequences. There is a need towards increasing the accuracy of MRI, especially for posttreatment evaluation. The term multiparametric MRI implies addition of functional sequences, namely, diffusion and perfusion to the routine protocol. This review summarizes the technique, potential implications and previously published studies about multiparametric MRI of rectal cancer.

Noninvasive Biomarkers of Colorectal Cancer: Role in Diagnosis and Personalised Treatment Perspectives

Colorectal cancer (CRC) is the third leading cause of cancer-related deaths worldwide. It has been estimated that more than one-third of patients are diagnosed when CRC has already spread to the lymph nodes. One out of five patients is diagnosed with metastatic CRC. The stage of diagnosis influences treatment outcome and survival. Notwithstanding the recent advances in multidisciplinary management and treatment of CRC, patients are still reluctant to undergo screening tests because of the associated invasiveness and discomfort (e.g., colonoscopy with biopsies). Moreover, the serological markers currently used for diagnosis are not reliable and, even if they were useful to detect disease recurrence after treatment, they are not always detected in patients with CRC (e.g., CEA). Recently, translational research in CRC has produced a wide spectrum of potential biomarkers that could be useful for diagnosis, treatment, and follow-up of these patients. The aim of this review is to provide an overview of the newer noninvasive or minimally invasive biomarkers of CRC. Here, we discuss imaging and biomolecular diagnostics ranging from their potential usefulness to obtain early and less-invasive diagnosis to their potential implementation in the development of a bespoke treatment of CRC.

Organ preservation in rectal cancer: a synopsis of current guidelines

BACKGROUND

The high morbidity associated with radical resection for rectal cancer is an incentive for surgeons to adopt strategies aimed at organ preservation, particularly for early disease. There are a number of different approaches to achieve this. In this study we have collated current national and international guidelines to produce a synopsis to support this changing practice.

METHODS

The databases PubMed, Embase, Trip database, national guideline clearinghouse, BMJ Best practice were interrogated. Guidelines published before 2010 were excluded. The AGREE-II tool was used for quality assessment.

RESULTS

24 guidelines were drawn from 2278 potential publications. A consensus exists for local excision for "low risk" T1 rectal cancer but there is no agreement how to stratify the risk of treatment failure. There is a low level of agreement for rectal preservation for more advanced disease but when mentioned is recommended for unfit patients or in th context of a clinical trial. Guidelines are inconsistent with respect to surveillance in node negative disease and after, complete response to chemoradiotherapy CONCLUSION: According to current guidelines and consensus statements organ preservation for rectal cancer beyond low risk T1, is still considered experimental and only indicated in patients unsuitable for radical surgery.. Follow up strategies and cN0 staging deserve attention and highlight the need for high quality clinical trials. This article is protected by copyright. All rights reserved.

Diffusion imaging of the vertebral bone marrow

Diffusion-weighted MRI (DWI) of the vertebral bone marrow is a clinically important tool for the characterization of bone-marrow pathologies and, in particular, for the differentiation of benign (osteoporotic) and malignant vertebral compression fractures. DWI of the vertebral bone marrow is, however, complicated by some unique MR and tissue properties of vertebral bone marrow. Due to both the spongy microstructure of the trabecular bone and the proximity of the lungs, soft tissue, or large vessels, substantial magnetic susceptibility variations occur, which severely reduce the magnetic field homogeneity as well as the transverse relaxation time T^*₂ , and thus complicate MRI in particular with echoplanar imaging (EPI) techniques. Therefore, alternative diffusion-weighting pulse sequence types such as single-shot fast-spin-echo sequences or segmented EPI techniques became important alternatives for quantitative DWI of the vertebral bone marrow. This review first describes pulse sequence types that are particularly important for DWI of the vertebral bone marrow. Then, data from 24 studies that made diffusion measurements of normal vertebral bone marrow are reviewed; summarizing all results, the apparent diffusion coefficient (ADC) of normal vertebral bone marrow is typically found to be between 0.2 and 0.6 × 10^-3  mm² /s. Finally, DWI of vertebral compression fractures is discussed. Numerous studies demonstrate significantly greater ADCs in osteoporotic fractures (typically between 1.2 and 2.0 × 10^-3  mm² /s) than in malignant fractures or lesions (typically 0.7-1.3 × 10^-3  mm² /s). Alternatively, several studies used the (qualitative) image contrast of diffusion-weighted acquisitions for differentiation of lesion etiology: a very good lesion differentiation can be achieved, particularly with diffusion-weighted steady-state free precession sequences, which depict malignant lesions as hyperintense relative to normal-appearing vertebral bone marrow, in contrast to hypointense or isointense osteoporotic lesions. Copyright © 2015 John Wiley & Sons, Ltd.

Water and lipid diffusion MRI using chemical shift displacement-based separation of lipid tissue (SPLIT)

PURPOSE

To obtain water and lipid diffusion-weighted images (DWIs) simultaneously, we devised a novel method utilizing chemical shift displacement-based separation of lipid tissue (SPLIT) imaging.

MATERIALS AND METHODS

Single-shot diffusion echo-planar imaging without fat suppression was used and the imaging parameters were optimized to separate water and lipid DWIs by chemical shift displacement of the lipid signals along the phase-encoding direction. Using the optimized conditions, transverse DWIs at the maximum diameter of the right calf were scanned with multiple b-values in five healthy subjects. Then, apparent diffusion coefficients (ADCs) were calculated in the tibialis anterior muscle (TA), tibialis bone marrow (TB), and subcutaneous fat (SF), as well as restricted and perfusion-related diffusion coefficients (D and D*, respectively) and the fraction of the perfusion-related diffusion component (F) for TA.

RESULTS

Water and lipid DWIs were separated adequately. The mean ADCs of the TA, TB, and SF were 1.56±0.03mm²/s, 0.01±0.01mm²/s, and 0.06±0.02mm²/s, respectively. The mean D*, D, and F of the TA were 13.7±4.3mm²/s, 1.48±0.05mm²/s, and 4.3±1.6%, respectively.

CONCLUSION

SPLIT imaging makes it possible to simply and simultaneously obtain water and lipid DWIs without special pulse sequence and increases the amount of diffusion information of water and lipid tissue.

Diffusion-weighted magnetic resonance imaging in colorectal cancer

Magnetic resonance imaging (MRI) plays now a major role in patients with colorectal cancer regarding tumor staging, surgical planning, therapeutic decision, assessment of tumor response to chemoradiotherapy and surveillance of rectal cancer, and detection and characterization of liver or peritoneal metastasis of colorectal cancers. Diffusion-weighted MRI (DW-MRI) is a functional imaging tool that is now part of the standard MRI protocol for the investigation of patients with colorectal cancer. DW-MRI reflects micro-displacements of water molecules in tissues and conveys high degrees of accuracy to discriminate between benign and malignant colorectal conditions. Thus, in addition to morphological imaging, DW-MRI has an important role to accurately detect colorectal neoplasms and peritoneal implants, to differentiate benign focal liver lesions from metastases and to detect tumor relapse within fibrotic changes. This review provides a comprehensive overview of basic principles, clinical applications and future trends of DW-MRI in colorectal cancers.

Diffusion-weighted MRI in Crohn's disease: Current status and recommendations

Over the past years, technological improvements and refinements in magnetic resonance imaging (MRI) hardware have made high-quality diffusion-weighted imaging (DWI) routinely possible for the bowel. DWI is promising for the detection and characterization of lesions in Crohn's disease (CD) and has been advocated as an alternative to intravenous gadolinium-based contrast agents. Furthermore, quantification using the apparent diffusion coefficient may have value as a biomarker of CD activity and has shown promise. In this article we critically review the literature pertaining to the value of DWI in CD for detection, characterization, and quantification of disease activity and complications. Although the body of supportive evidence is growing, it is clear that well-designed, multicenter studies are required before the role of DWI in clinical practice can be fully established. J. Magn. Reson. Imaging 2016;44:1381-1396.