Chapter 11 Flashcards
when pathology cannot be differentiated sufficiently using conventional pulse sequences, the use of __ to __ is useful
contrast agents; T1 or T2 contrast
because MR relaxation mechanisms determine image contrast, the latter can be changed for pathology by modifying __
the magnetic susceptibility of tissues, and thereby relaxation rate
the most common contrast agent contains __, which is a rare-earth metal with __
gadolinium (Gd); strong paramagnetic properties above 20 degrees C
Gd-based contrast agents can shorten __ by a substantial amount, which can enhance __
T1 recovery time; contrast in brain regions where it is present
slide 3 images
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molecular tumbling rate refers collectively to the processes of molecular __ (3)
translation, rotation, and vibration
the closer the molecular tumbling frequency is to the Larmor frequency, the easier it is for __ to occur and the shorter __ is
spin-lattice relaxation; T1
if the molecule has __, molecular tumbling affects the local magnetic field, and the addition of a contrast agent __
a magnetic moment; amplifies such effects
if a Gd contrast agent with a large magnetic moment is added to water, the __ is shortened because __
T1 of the water; the tumbling rate of Gd is near the Larmor frequency of water
image from slide 4
Gd is a __ element with __ electrons which have very strong __, resulting in large changes in the __
trivalent lanthanide; unpaired; magnetic moments; local magnetic field
the large number of __ in the outer shells of Gd indicates the ability of this element to have __
unpaired electrons; a strong magnetic moment
when Gd compounds are introduced into the body, it can shorten not only the __ but also __
T1 of water; its T2
when Gd contrast agents are administered during dynamic brain imaging, it is delivered __ the degree of which can be monitored by __
to brain tissues via blood perfusion; tracking the uptake of the contrast agent
tumors have __ uptake of blood due to the phenomenon of __, so the contrast agent __
higher; angiogenesis; concentrates at the tumor location
images from slide 6
relaxivity is the extent to which a substance __
modifies the relaxation rate of a tissue
there are a large number of Gd-based compounds with __ and there has been much research devoted to the development of __ due to __
high relaxivities; novel agents with higher relaxivities; safety issues
the dose of a contrast agents which can safely be administered to a patient is computed based on __
the weight of the patients and the nature of the agent
like mercury (Hg) and lead (Pb), free Gd atoms __, __, and __. this can result in __
bind easily to cell membranes, transport proteins, enzymes, and are difficult to excrete via usual metabolic pathways; accumulation of such metals and subsequent poisoning
__ is perhaps the most common contrast agent
Gd-DTPA (Magnevist)
Gd-DTPA is used to image __, __ or __
intracerebral lesions, abnormal vascularity due to tumors, or abnormalities in the BBB
in the complex of Gd3+ and DTPA5- the Gd ion is 9-coordinate, surrounded by 3 N atoms and 5 O atoms from the carboxylate groups. the 9th coordination site is occupied by a labile water molecule
___
image from slide 8
contrast agents are ideal for localizing __ as well as __
some healthy structures; breakdowns in the BBB
healthy structures localized by Gd (5):
falx cerebri, choroid plexus, pineal and pituitary glands, veins (slow-moving blood)
abnormalities w/ intact BBB (4):
acoustic neurons, meningiomas, micro- and macro-adenomas
abnormalities w/BBB breakdown (2):
infarcts; some tumors (e.g. metastases, especially in vertebrae)
images from slide 9
