While conventional MRI sequences remain useful, adjunct sequences are now available that are easily integrated into a routine MRI tumor protocol, to enhance the utility of MRI for disease characterization, assessment of treatment response and the detection of tumor recurrence following surgery. Specifically, non-contrast MRI techniques (such as quantitative DWI and chemical shift imaging) are fast and non-invasive and provide valuable information for the evaluation of sarcomas. MR spectroscopy is not in common clinical use for the assessment of sarcomas, although it is a technique that may provide information regarding the metabolic pathways of sarcoma development.
1. MRI is central to the assessment of extent of disease of a sarcoma.
2. While conventional MRI sequences remain useful, adjunct sequences are now available that are easily integrated into a routine MRI tumor protocol, to enhance the utility of MRI for disease characterization, assessment of treatment response and the detection of tumor recurrence following surgery.
3. Non-contrast MRI techniques (such as quantitative DWI and chemical shift imaging) are fast and non-invasive and provide valuable information for the evaluation of sarcomas.
Conventional MRI sequences that are used for the assessment of sarcomas include spin echo T1-weighted imaging, fluid-sensitive sequences (fat-suppressed T2-weighted or STIR) and static post-contrast T1-weighted imaging. Advances in volumetric gradient echo techniques, especially in combination with subtraction imaging, have enabled the use of high resolution post-contrast imaging with multiplanar capability.
Several adjunct techniques are available, that may be easily integrated into a routine clinical protocol. These include the following:
a) Chemical shift imaging with in-phase and oppose-phase imaging
b) Quantitative diffusion weighted imaging with ADC mapping
c) Proton MR spectroscopy
d) Dynamic contrast-enhanced imaging
While conventional MRI sequences are the mainstay tools for defining the extent of disease of a sarcoma, adjunct sequences including chemical shift imaging, DWI and proton MRS are useful noncontrast techniques that further the applications of MRI to include disease characterization, assessment of treatment response, detection of recurrence following surgery.
For bone tumors, spin echo T1 weighted imaging is essential for determining the extent of disease, and contrast is generally not needed for this purpose. Chemical shift imaging is further used to characterize a bone marrow signal abnormality for the presence of marrow replacement (as would be seen by a tumor). For soft tissue tumors, contrast is helpful in delineating disease extent in the perilesional regions.
Quantitative diffusion weighted imaging (with ADC mapping) is helpful for detecting bone metastases, determining treatment response, separating benign from malignant disease and distinguishing nodular scar from recurrent tumor.
Proton MR spectroscopy has been studied for the evaluation of tumors, particularly for the characterization of lesions in the de novo setting. Proton MRS has been noted for its high negative predictive value for ruling out malignancy and is also potentially useful for assessing treatment response and tumor heterogeneity, although it is not in clinical use at this time.
Dynamic contrast enhanced imaging provides information regarding the vascularity of de novo tumors, important to characterizing malignancy and is similarly useful for distinguishing post-treatment granulation tissue from residual viable tumor or post-operative recurrence.
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