**5. Contrast**

The contrast agent used is a paramagnetic metal called gadolinium (GDL). It is associated with a water-soluble component diethylenetriaminepentaacetic acid (DTPA) that acts on the damaged tissues facilitating their identification [17, 18].

It is administered intravenously at a dose of 0.2 mL/kg on T1-weighted images through section planes determined according to the location and type of injury [17,18].

Patients who receive contrast are asked to abstain from all food and liquid for two hours in order to avoid adverse effects [17,18].

Local lesions are studied for the presence or absence, type, and thickness of the damaged tissues. The determination of the type of lesion is accomplished through changing the signal presented by damaged tissues in relation to normal tissue. The classification of injured tissues into hypointense or hyperintense, depends on the signal intensity (darker or lighter) visualized on the images during the screenings and on an expert testimony (Figure 10) [17,18].

In (A) are representative protons of a tissue section. Soon after a 90-degree pulse, the protons are on the same transverse plane and in phase with each other. Their magnetic vectors all point in the same direction. (B) After a very short period of time, these protons are out of phase, and their magnetic vectors are pointing to different directions. This decreases the power of the transverse magnetization vector Mxy. (C) T2 is shown as the time interval required for the

40 Imaging and Radioanalytical Techniques in Interdisciplinary Research - Fundamentals and Cutting Edge Applications

**Figure 9.** T2 shown as the time interval required for the transverse magnetization drops to 37% of its original

The contrast agent used is a paramagnetic metal called gadolinium (GDL). It is associated with a water-soluble component diethylenetriaminepentaacetic acid (DTPA) that acts on the

It is administered intravenously at a dose of 0.2 mL/kg on T1-weighted images through section

Patients who receive contrast are asked to abstain from all food and liquid for two hours in

Local lesions are studied for the presence or absence, type, and thickness of the damaged tissues. The determination of the type of lesion is accomplished through changing the signal presented by damaged tissues in relation to normal tissue. The classification of injured tissues into hypointense or hyperintense, depends on the signal intensity (darker or lighter) visualized

on the images during the screenings and on an expert testimony (Figure 10) [17,18].

damaged tissues facilitating their identification [17, 18].

order to avoid adverse effects [17,18].

planes determined according to the location and type of injury [17,18].

transverse magnetization drops to 37% of its original value [16].

value [3].

**5. Contrast**

**Figure 10.** Normal tissue in MRI in axial sections in the "spin echo" sequence taken from the lower limbs (calf) in T1 pre (A) and (B) post-contrast injection, T2 relaxation times (C) and inversion-recovery" sequence (D) used to promote sup‐ pression or fat saturation [16].

In these images, the tissues present themselves with their normal callibre vascular structures and anatomic topography, as well as their musculature with preserved sign and normal morphological aspect. The images also present the bone structure of their cortical portions and characteristic medullar signal, and preserved anatomical aspect [16].

For images of the central nervous system, "Figure 11" illustrates the characteristics in normal tissue relaxation time T1 before and after contrasts, which are used to differentiate normal tissue from the pathological ones [19,20].

**Figure 11.** Image of a normal central nervous system (sagittal plane) on pre-contrast (A) and post-contrast (B) sequen‐ ces spin-echo T1-weighted images.

Note all structures with normal anatomic aspects with enhancement in sequence with contrast, indicated by arrows [21].
