ROLE OF MR IMAGING IN EVALUATION OF RECTAL CANCER
Feras Mahmoud Rajab;
Abstract
MRI is an excellent modality to accurately stage primary rectal tumors and assess tumor response to neoadjuvant therapy.
With adequate experience, the radiologist can use this information to help the surgeon decide the course a patient would take from diagnosis to the ideal outcome, that is, cure.
MRI has proven its value in T staging but like other modalities is limited in its ability to provide an accurate N stage. There is some controversy regarding the optimal protocol, but high-resolution T2-weighted images serve as the gold standard for tumor evaluation.
Use of rectal distension, intravenous contrast, and lymph node–specific agents represents current areas of controversy that warrant further study.
In locally advanced rectal cancers, MR imaging can help determine relationship between the tumor and the surrounding pelvic structures.
Real improvement in lymph node characterization will come with the use of ultra-small iron-based particles, These particles are selectively taken up by the reticuloendothelial cells in normal lymph nodeswhich thus have low signal intensity on proton-density-weighted and T2-weighty MR images, Pathologic lymph nodes, with reticuloendothelial cells replaced by neoplastic cells, will not take up the contrast agent and thus will have a relatively bright signal intensity.
Early results using body coil MRI to stage rectal carcinoma were disappointing.with accuracy compared with histology of only 60%.coils, whichprovidedhigherSNRs,resultedinimproved accuracy of81%-89%,but werelimitedbypatient discomfort aswellasexpense,astheyareoften disposabledevices. Subsequentuseofphased-array pelvic coilMRI,withitsincreasedFOVandabilityto image theentire pelvis.
Role of Intravenous Contrast has been questioned in recent literature. It had been proposed that intravenous contrast administration would help delineate areas of viable tumor within spiculations that are seen on both pre-and post-treatment images. However, studies haves shown that the addition of gadolinium doesnot improve the radiologist’s ability to determine posttreatment fibrosis or desmoplastic reaction vs tumor.
In rectal cancer evaluation and follow-up, DWI is one of the techniques that has proven beneficial in differentiating post treatment fibrosis from residual tumor. And by Using Perfusion Imaging which is An additional means of determining tumor response to treatment is using measures of vascular permeability on dynamic contrast-enhanced images to calculate K trans values. Similar to diffusion-weighted imaging, a region of interest is drawn around the enhancing tumor, and this value is used to calculate vascular permeability, or K trans. Tumors with lower K trans values following treatment indicate a favorable response to therapy.
With adequate experience, the radiologist can use this information to help the surgeon decide the course a patient would take from diagnosis to the ideal outcome, that is, cure.
MRI has proven its value in T staging but like other modalities is limited in its ability to provide an accurate N stage. There is some controversy regarding the optimal protocol, but high-resolution T2-weighted images serve as the gold standard for tumor evaluation.
Use of rectal distension, intravenous contrast, and lymph node–specific agents represents current areas of controversy that warrant further study.
In locally advanced rectal cancers, MR imaging can help determine relationship between the tumor and the surrounding pelvic structures.
Real improvement in lymph node characterization will come with the use of ultra-small iron-based particles, These particles are selectively taken up by the reticuloendothelial cells in normal lymph nodeswhich thus have low signal intensity on proton-density-weighted and T2-weighty MR images, Pathologic lymph nodes, with reticuloendothelial cells replaced by neoplastic cells, will not take up the contrast agent and thus will have a relatively bright signal intensity.
Early results using body coil MRI to stage rectal carcinoma were disappointing.with accuracy compared with histology of only 60%.coils, whichprovidedhigherSNRs,resultedinimproved accuracy of81%-89%,but werelimitedbypatient discomfort aswellasexpense,astheyareoften disposabledevices. Subsequentuseofphased-array pelvic coilMRI,withitsincreasedFOVandabilityto image theentire pelvis.
Role of Intravenous Contrast has been questioned in recent literature. It had been proposed that intravenous contrast administration would help delineate areas of viable tumor within spiculations that are seen on both pre-and post-treatment images. However, studies haves shown that the addition of gadolinium doesnot improve the radiologist’s ability to determine posttreatment fibrosis or desmoplastic reaction vs tumor.
In rectal cancer evaluation and follow-up, DWI is one of the techniques that has proven beneficial in differentiating post treatment fibrosis from residual tumor. And by Using Perfusion Imaging which is An additional means of determining tumor response to treatment is using measures of vascular permeability on dynamic contrast-enhanced images to calculate K trans values. Similar to diffusion-weighted imaging, a region of interest is drawn around the enhancing tumor, and this value is used to calculate vascular permeability, or K trans. Tumors with lower K trans values following treatment indicate a favorable response to therapy.
Other data
| Title | ROLE OF MR IMAGING IN EVALUATION OF RECTAL CANCER | Other Titles | دور الرنين المغناطيسي في تقييم سرطان المستقيم | Authors | Feras Mahmoud Rajab | Issue Date | 2015 |
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