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    • br Basis and methodology of

    2019-05-13


    Basis and methodology of DCE-MRI DCE-MRI images are performed by using injecting low-molecular-weight gadolinium chelated contrast agent with a constant, stable rate. The contrast agent is carried by blood flow into the tissue, causing increased signal intensity (SI) of the T1-weighted images due to the shortening of relaxation time of the tissue. Within the tissue, the contrast agent passes from the Since first used in to the capillaries, and then permeates to the extravascular extracellular space (EES). The rate of contrast agent extravasation to EES in the tumor tissue is determined by vessel leaky and blood flow. Thus, the signal counted on DCE-MRI represents a combination of permeability and tissue perfusion. DCE-MRI is sensitive to alterations in vascular permeability, extracellular space, and blood flow. To ideally record the signal change in the supplying blood vessel and within the tumor, a regular injection rate of the contrast agent captured with proper temporal resolution according to the flow rate of the investigated tissue is recommended. This signal enhancement of bone marrow perfusion can be quantified either with a semi-quantitative or quantitative analysis. The semi-quantitative analysis is based on the calculation of heuristic parameters that can be easily extracted from SI curves. In contrast, the quantitative analysis needs model-based curve fitting algorithms using a bi-compartmental model as well as arterial input function. The parameters from both analysis methods have been shown to present correlation with bone marrow angiogenesis and MVD by immune-histochemical stain from biopsy tissue counting. Our research protocols for the use of DCE-MRI of BM perfusion and angiogenesis measurement have been described previously. In brief, DCE-MRI was performed at the midsection of vertebral bodies from T11 to sacrum, and the values of signal from L2 to L4 were measured by a radiologist and plotted as a time–SI curve. The time–SI curve was then fitted by the Mathematica (v 6.1) software (Wolfram Research, Champaign, IL) using a nonlinear curve-fitting function. The baseline SI (SI base) on a time–SI curve was defined as the mean SI for the first five images, and the maximum SI (SI max) was defined as the maximum value of the first rapidly rising part of the curve. We usually set the total duration of DCE-MRI examination at 600 s to track the uptake kinetics of contrast agents. The contrast enhancement rise time (T rise) was defined as the time between SI base and SI max. The two semi-quantitative parameters, Peak and Slope, were calculated as (SI max − SI base)/SI base and (SI max − SI base)/T rise, respectively. On the other hand, the angiogenesis parameters based on DCE-MRI could be described by three model quantitative parameters, Amp, Kep, and Kel, calculated using the bi-compartmental model. Data for each patient were represented as the average for the parameters of vertebral bodies from L2 to L4. Among these semi-quantitative and quantitative parameters, Peak indicates the contrast material in the intra- and extra-vascular interstitial spaces, representing tissue perfusion; Slope predominantly indicates the contrast agent in the intravascular space, which is determined by tissue vascularization and perfusion as well as capillary permeability; Amp is similar to Slope but provides better quantification of vascularity. The efflux rate constant is represented as Kep, which indicates the permeability. The Kep parameter is a rate transfer coefficient. More details about the measurement methods were listed as below:
    Semi-quantitative analysis The semi-quantitative analysis is widely used because it is easy to calculate without the need of modeling. However, these parameters are highly affected by the factor of the acquisition systems, contrast media volume and injection rate, because the true concentration of contrast agent in the tissues is not estimated. Thus, differences in temporal resolution and injection rates can easily change the shape and amplitude of SI curves, making comparison and quantification difficult. Moreover, these descriptive parameters provide no physiologic meaning into the behavior of the tumor vessels.