Chapter 11

Question 1

when pathology cannot be differentiated sufficiently using conventional pulse sequences, the use of __ to __ is useful

Answer 1

contrast agents; T1 or T2 contrast

Question 2

because MR relaxation mechanisms determine image contrast, the latter can be changed for pathology by modifying __

Answer 2

the magnetic susceptibility of tissues, and thereby relaxation rate

Question 3

the most common contrast agent contains __, which is a rare-earth metal with __

Answer 3

gadolinium (Gd); strong paramagnetic properties above 20 degrees C

Question 4

Gd-based contrast agents can shorten __ by a substantial amount, which can enhance __

Answer 4

T1 recovery time; contrast in brain regions where it is present

Question 5

slide 3 images

Answer 5

–

Question 6

molecular tumbling rate refers collectively to the processes of molecular __ (3)

Answer 6

translation, rotation, and vibration

Question 7

the closer the molecular tumbling frequency is to the Larmor frequency, the easier it is for __ to occur and the shorter __ is

Answer 7

spin-lattice relaxation; T1

Question 8

if the molecule has __, molecular tumbling affects the local magnetic field, and the addition of a contrast agent __

Answer 8

a magnetic moment; amplifies such effects

Question 9

if a Gd contrast agent with a large magnetic moment is added to water, the __ is shortened because __

Answer 9

T1 of the water; the tumbling rate of Gd is near the Larmor frequency of water

Question 10

image from slide 4

Question 11

Gd is a __ element with __ electrons which have very strong __, resulting in large changes in the __

Answer 11

trivalent lanthanide; unpaired; magnetic moments; local magnetic field

Question 12

the large number of __ in the outer shells of Gd indicates the ability of this element to have __

Answer 12

unpaired electrons; a strong magnetic moment

Question 13

when Gd compounds are introduced into the body, it can shorten not only the __ but also __

Answer 13

T1 of water; its T2

Question 14

when Gd contrast agents are administered during dynamic brain imaging, it is delivered __ the degree of which can be monitored by __

Answer 14

to brain tissues via blood perfusion; tracking the uptake of the contrast agent

Question 15

tumors have __ uptake of blood due to the phenomenon of __, so the contrast agent __

Answer 15

higher; angiogenesis; concentrates at the tumor location

Question 16

images from slide 6

Question 17

relaxivity is the extent to which a substance __

Answer 17

modifies the relaxation rate of a tissue

Question 18

there are a large number of Gd-based compounds with __ and there has been much research devoted to the development of __ due to __

Answer 18

high relaxivities; novel agents with higher relaxivities; safety issues

Question 19

the dose of a contrast agents which can safely be administered to a patient is computed based on __

Answer 19

the weight of the patients and the nature of the agent

Question 20

like mercury (Hg) and lead (Pb), free Gd atoms __, __, and __. this can result in __

Answer 20

bind easily to cell membranes, transport proteins, enzymes, and are difficult to excrete via usual metabolic pathways; accumulation of such metals and subsequent poisoning

Question 21

__ is perhaps the most common contrast agent

Answer 21

Gd-DTPA (Magnevist)

Question 22

Gd-DTPA is used to image __, __ or __

Answer 22

intracerebral lesions, abnormal vascularity due to tumors, or abnormalities in the BBB

Question 23

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

Answer 23

___

Question 24

image from slide 8

Question 25

contrast agents are ideal for localizing __ as well as __

Answer 25

some healthy structures; breakdowns in the BBB

Question 26

healthy structures localized by Gd (5):

Answer 26

falx cerebri, choroid plexus, pineal and pituitary glands, veins (slow-moving blood)

Question 27

abnormalities w/ intact BBB (4):

Answer 27

acoustic neurons, meningiomas, micro- and macro-adenomas

Question 28

abnormalities w/BBB breakdown (2):

Answer 28

infarcts; some tumors (e.g. metastases, especially in vertebrae)

Question 29

images from slide 9