![]() Ltd., Bracco, Kiran, Bruker, GE Healthcare, Chematech, MEDTRON AG, Reveal Pharmaceuticals, ESAOTE SPA, Accelius Global, Opakim Tibbi Urunler San. Ltd., Guerbet, JB Pharma, Jodas Expoim Pvt. It is field strength- dependent, with the effect increasing as the square of the field strength.Beijing Beilu Pharmaceutical Co. This kind of effect is referred to as susceptibility effect. However, their principal effect is a reduction in T2*.įor this reason, the effects of such contrast agents are best observed using gradient echo sequences where T2* effects are retained. T2 is reduced due to the diffusion of water through these field gradients. iron oxides).įerro- and superparamagnetic contrast agents produce local magnetic field gradients which disrupt the homogeneity of the local magnetic field. Magnetite, Fe 3O 4, is such a superparamagnetic particle.Ĭoated with an inert resin, magnetites can be used for oral or intravenous applications (cf. Depending on their particle size and coating, these compounds can also become T1 agents. If one reduces their size, they lose their permanent magnetic characteristics and are then called superparamagnetic particles. ![]() ![]() Ferromagnetic agents consist of particles which show permanent magnetism. Superparamagnetic and ferromagnetic agents belong to the group of negative agents. This darkens the region of interest (Figure 13-02 and Figure 13-03). Negative contrast agents influence signal intensity usually by shortening T2* and T2. With negative contrast agents, T2 relaxation is accelerated signal intensity is lower (light blue curve in the "TR" part of the graph this curve overlaps with the red curve). Only a T1-weighted sequence (in this case a spin echo sequence) with short TE highlights this contrast enhancement. Therefore, at a given TR, signal intensity (yellow curve) is higher than in the same tissue without contrast agent (red curve). T1 relaxation is accelerated by positive agents, and the spins recover faster. Influence of a positive (T1) and negative (T2, T2*) contrast agent upon signal intensity (SI). However, the contrast-enhanced MR images (postcontrast: b and d) show a large number of metastases. The plain MR images (precontrast: a and c) do not reliably reveal brain lesions. This figure gives an example of a clinical case where only the application of such a positive contrast agent helped the diagnostic process and showed the extent of the disease: Patient with breast cancer and recent neurological symptoms. Paramagnetic agents are mainly used to shorten T1 relaxation and thus brighten the region of interest, whereas ferro- and superparamagnetic agents shorten T2 and T2* and thus darken the image (red arrows). Influence of positive (T1) and negative (T2, T2*) MR contrast agents upon signal intensity. Thus, tissues taking up such agents will become bright in a T1-weighted sequence (Figure 13-02 and Figure 13-03). Their effect on T1 and T2 is similar, but since T1 of tissues is much higher than T2, the predominant effect at low doses is that of T1 shortening. ![]() ![]() Paramagnetic contrast agents, with the exception of dysprosium-based preparations, are called positive agents. As seen in Table 13-02, with its seven unpaired electrons gadolinium is best suited for this purpose, followed by manganese. However, in most substances the electrons are paired, resulting in a weak net magnetic field. The magnetic field produced by an electron is much stronger than that produced by a proton. 13-02 Positive and Negative Contrast Agents ![]()
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