MR Contrast Agents and Blood

MR Contrast Agents and Blood Quiz

MR Contrast: Physics & Clinical

  1. The element gadolinium is part of which periodic table group?
    1. Lanthanides
    2. Actinides
    3. Alkaline-earth metals
    4. Transition metals

    Gadolinium, element number 64, is located in the exact middle of the lanthanide series of rare-earth elements. Link to Q&A discussion

  2. The paramagnetic properties of gadolinium that make it suitable for a contrast agent derive from its
    1. Odd number of protons
    2. Odd number of protons and neutrons together
    3. Unpaired inner shell electrons
    4. Paired electrons in bonding orbitals

    Although all elements with odd numbers of nucleons possess nuclear paramagnetism, (responsible for the NMR phenomenon), this is extremely weak except in the immediate vicinity of the nucleus. Because electrons have the same spin (½) but a much smaller size than protons, their gyromagnetic ratios are 657 times larger, giving them powerful magnetic moments. It is unpaired inner shell electrons that give gadolinium its paramagnetic properties. Link to Q&A discussion

  3. In its 4f shell, gadolinium has
    1. 4 unpaired electrons
    2. 7 unpaired electrons
    3. 4 paired and 3 unpaired electrons
    4. 7 paired electrons

    The 4f electron shell has seven available positions, each of which may potentially be occupied by a lone electron or an electron pair. According to Hund’s rule of maximum multiplicity, electrons will occupy each position singly before filling them in pairs. Gadolinium has seven electrons available to fill the 4f shell, and they are all unpaired. Link to Q&A discussion

  4. How many of gadolinium’s unpaired 4f shell electrons participate in bonding/chelation when made into a contrast agent?
    1. 0
    2. 1
    3. 4
    4. 7

    None of gadolinium’s 4f shell electrons are directly involved in bonding, thus retaining its powerful paramagnetic properties when formulated as a contrast agent. Link to Q&A discussion

  5. If gadolinium is chelated with a very large molecule (like albumin), what happens to its T1 relaxation time?
    1. It remains unchanged
    2. It shortens
    3. It lengthens
    4. It becomes shorter than T2

    Smaller aqueous contrast agents (like Gd-DTPA) tumble too quickly to be highly efficient at T1 relaxation. If the contrast agent attaches to a very large molecule (such as albumin), its motion slows to a range much closer to the Larmor frequency and its T1 relaxation time shortens dramatically. Note that choice (d) is impossible, as T1 is always greater than or equal to T2. Link to Q&A discussion

  6. Which of the following statements about inner sphere and outer sphere relaxation effects is false?
    1. On a molecule-by-molecule basis, inner sphere relaxation is much more powerful than outer sphere relaxation.
    2. Inner sphere relaxation requires very close approach of a water molecules to the gadolinium metallic center.
    3. Although weaker on a per molecule basis, outer sphere effects are important because they involve larger numbers of water molecules.
    4. Most gadolinium contrast agents have multiple coordination sites available for inner sphere relaxation to take place.

    A consequence of its electron structure is that the Gd+3 ion typically exhibits nine coordination sites for bonding and chemical interactions. In all MR contrast agents now commercially available, a ligand group occupies eight of these sites while the ninth is available for transient bonding by a solvent water molecule for an inner sphere effect to occur. So choice (d) is false. Link to Q&A discussion

  7. The T1- and T2-relaxivities of a contrast agent are given in what units?
    1. L/mmol-s
    2. mmol/s
    3. L/mmol
    4. unitless

    The relaxivity of an MR contrast agent reflects how the relaxation rates of a solution change as a function of concentration [C]. Since a contrast agent may affect the two relaxation rates (1/T1 and 1/T2) individually, there are two corresponding relaxivities, denoted r1 and r2. By definition, 1/ΔT1 = r1 [C] and 1/ΔT2 = r2 [C]. Since ΔT1 and ΔT2 are given in seconds and [C] is measured in millimoles per liter, r1 and r2 have units of L/mmol-s. Link to Q&A discussion

  8. In which of the following scenarios would the T2-shortening effects of gadolinium not be expected to be seen?
    1. MR of the bladder
    2. MR arthography
    3. Late enhancement phase cardiac MRI
    4. MR venography

    In routine MR imaging, the mild T2-shortening effects of low doses of gadolinium (which decrease signal intensity) are usually overwhelmed by the more dominant T1-shortening effects (which increase signal intensity) and are therefore not normally observed. When high concentrations of contrast are present, low-T2 effects may predominate. This is seen routinely in MRI of the urinary tract, occasionally in MR arthrograms and venograms (where high concentrations of gadolinium are injected directly into joints or vessels); and in the "first pass" of gadolinium contrast through the vascular system on dynamic contrast enhanced (DCE) studies or time-resolved MR angiography. It would not be seen in late phase imaging of the myocardium. Link to Q&A discussion

  9. Concerning gadolinium enhancement as a function of field strength, which statement is true?
    1. All currently used contrast agents demonstrate a slight increase in T1-relaxivity with increasing field strength.
    2. Contrast agents with lower T1 relaxivities (r1) values produce stronger enhancement.
    3. The same dose of contrast will typically generate more enhancement at 1.5T than 0.5T.
    4. Lower doses of contrast agents are needed at low-field compared to high-field.

    Only (c) is true. Because tissue T1 values increase while contrast agent relaxivities are about the same or decrease only slightly with increasing field strength, the net effect is an increase in relative contrast enhancement as field strength increases Link to Q&A discussion

  10. Why do magnetization-transfer preparation pulses increase the visibility of gadolinium enhancement?
    1. They do not. This is a myth.
    2. They suppress the signal from background tissues.
    3. They shorten tissue T1.
    4. They interfere with gadolinium-water inner sphere relaxation.

    Because gadolinium (Gd) enhancement is caused by a water-Gd ion interaction (not macromolecular cross-relaxation), MT pulses suppress the signal from background tissues and render Gd-enhanced areas more conspicuous. Link to Q&A discussion

  11. The first commercially marketed gadolinium-based MR contrast agent was
    1. Dotarem®
    2. Magnevist®
    3. MultiHance®
    4. Omniscan®

    Magnevist®, marketed by Berlex Imaging (and subsequently acquired by Bayer), first received FDA approval in 1988. Link to Q&A discussion

  12. Which of the following agents is macrocyclic?
    1. Dotarem®
    2. Magnevist®
    3. MultiHance®
    4. Omniscan®

    Dotarem®, along with ProHance® and Gadavist®, are all macrocyclic. The others are linear in structure. Link to Q&A discussion

  13. Concerning gadoxetic acid constrast (Eovist®/Primovist®), which statement is false?
    1. Transient dyspnea after injection occurs in about 10% of patients.
    2. At least 90% of the administered dose is taken up by hepatocytes.
    3. Elimination is by both biliary excretion and glomerular filtration.
    4. Hepatic uptake and enhancement is decreased when bilirubin levels are elevated.

    Only about half of the administered dose is taken up by hepatocytes. The remainder behaves as other nonspecific extracelleular gadolinium contrast agents. Link to Q&A discussion

  14. Although no longer in production, what was unique about the liver contrast agent Teslascan™ sold in the 1990s and early 2000s?
    1. It was based on manganese.
    2. It was based on iron.
    3. It was based on copper.
    4. It was based on magnesium.

    To date the only manganese-based contrast agent ever approved for worldwide sales and clinical use was mangafodipir trisodium (Mn-DPDP), marketed in the 1990's under the tradename Teslascan™. Due to low sales, poor clinical performance, and concerns over toxicity, Teslascan™ was withdrawn from the US market in 2003 and from the EU in 2010. Link to Q&A discussion

  15. And speaking of MR contrast agents no longer in production, what was unique about Ablavar®?
    1. It was based on manganese.
    2. It was based on iron oxide.
    3. It attached to albumin and served as a blood pool agent.
    4. It was taken up by the reticuloendothelial system.

    Withdrawn as a product in 2017 by its manufacturer due to poor sales, Ablavar® had been designed specifically for vascular imaging. The drug underwent reversible bonding to plasma proteins (principally albumin) when injected into the blood, allowing it to be confined intravascularly for several hours. Link to Q&A discussion

  16. Concerning superparamagnetic iron oxides (SPIOs) and ultra-small superparamagnetic iron oxides (US-SPIOs), which statement is false?
    1. US-SPIOs may be injected intravascularly, intradermally, or subcutaneously.
    2. The larger SPIOs are especially useful for lymph node imaging.
    3. Their T1 and T2 relaxivities are 10-20 x greater than gadolinium contrast agents.
    4. Their accumulation in the liver, spleen, and bone marrow can be mistaken for hemochromatosis.

    Option (b) is false. The largest of these SPIO nanoparticles (50-100 nm) undergo rapid uptake by the liver. Smaller US-SPIO particles (5-50 nm), remain in the circulation and are cleared by lymphatics, draining into lymph nodes where they are captured and retained by macrophages/histiocytes (and potentially other sinus-lining endothelial cells). Link to Q&A discussion

  17. Concerning ferumoxytol (Feraheme®/Rienso®) which statement is false?
    1. It is now sold and marketed worldwide as an MR contrast agent.
    2. It has a long intravascular half-life after intravenous injection, behaving as a blood pool agent.
    3. It reduces both T1 and T2 relaxation times of the tissues wherein it accumulates.
    4. It must be given diluted and by slow intravenous injection.

    Although ferumoxytol was originally developed as an MR contrast agent, it was instead marketed and approved for intravenous treatment of iron-deficiency anemia associated with chronic renal disease. It has not yet received indications for use as an MR contrast agent. It’s use in this form is considered “off label”. Link to Q&A discussion

  18. Concerning bowel contrast materials, a large volume, water-based solution like VoLumen® would be classified as what type of contrast agent?
    1. Positive
    2. Negative
    3. Biphasic
    4. Neutral

    Biphasic contrast agents are all water-based, appearing dark on T1-weighted and bright on T2-weighted images. Biphasic enteric contrast agents like VoLumen® contain nonabsorbable additives (resins, polyethylene glycol, mannitol, sorbitol, or other sugar alcohols) that help draw in and retain intraluminal water. Link to Q&A discussion

  19. Concerning bowel contrast materials, a suspension of magnetite-based particles like GastroMARK® (ferumoxsil) would be classified as what type of contrast agent?
    1. Positive
    2. Negative
    3. Biphasic
    4. Neutral

    Negative contrast agents are designed to make the intraluminal contents dark, especially on T2-weighted images. GastroMARK® causes a remarkable drop in signal within the bowel lumen on both T1 and T2-weighted images. The darkening on T1-weighted images allows visualization of mucosal enhancement. Link to Q&A discussion

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MR Contrast Agents: Safety

  1. Compared to non-ionic iodine-based contrast agents, the frequency of acute adverse reactions to gadolinium-based contrast agents is
    1. About the same
    2. Slightly less
    3. Slightly more
    4. Much more

    Compared to many other drugs gadolinium contrast agents possess a very low incidence (<2.5%) of acute adverse reactions, mostly minor. Such rates are not too much higher than those occurring during placebo injection of saline and are about one-third as common as reaction rates recorded with nonionic iodine-based contrast media. Link to Q&A discussion

  2. Considering gadolinium-based contrast agents as a whole, what is the approximate rate of severe allergic reaction (e.g., facial edema, bronchospasm, hypotension, arrhythmias, widespread uticaria) expected?
    1. 1 in 500 patients
    2. 1 in 5000 patients
    3. 1 in 50,000 patients
    4. 1 in 500,000 patients

    Moderately severe hypersensitivity reactions (including bronchospasm, laryngospasm, facial edema, tachycardia, arrhythmias, or widespread urticaria) occur in about 1 in 5000 cases. Link to Q&A discussion

  3. Considering gadolinium-based contrast agents as a whole, what is the approximate risk of death from a severe allergic reaction?
    1. 1 in 4,000 patients
    2. 1 in 40,000 patients
    3. 1 in 400,000 patients
    4. 1 in 4,000,000 patients

    Worldwide, a number of severe anaphylactoid reactions to gadolinium-based MR contrast agents, including death, have been reported. The incidence of severe reactions is about 1 in 20,000 and the risk of death about 1 in 400,000. Link to Q&A discussion

  4. Which one of the following rare reactions to gadolinium has not been reported?
    1. Rhabdomyolysis
    2. Pancreatitis
    3. Encephalopathy
    4. Acute renal failure

    To my knowledge, acute rhabdomyolysis has never occurred following gadolinium administration. The other three have been rarely reported. Link to Q&A discussion

  5. Comparing “true” anaphylaxis and “anaphylactoid” reactions to gadolinium contrast, which statement is correct?
    1. They can be distinguished based on their clinical presentation.
    2. Both are IgE-mediated.
    3. Both cause release of vasoactive amines and inflammatory mediators from mast cells.
    4. Both are dose-related.

    "True" anaphylaxis is an IgE-mediated type 1 hypersensitivity reaction and is not dose-related. Anaphylactoid reactions have an identical clinical pattern to "true" anaphylaxis but are not IgE-mediated. The two cannot be distinguished clinically. Both cause the same effect on basophils and mast cells to release histamine and other contents. Link to Q&A discussion

  6. Which of the following statements about the clinical features of nephrogenic systemic fibrosis (NSF) is incorrect?
    1. Nearly all reported cases have been in patients with severe renal disease or insufficiency.
    2. Skin thickening and joint contractures are characteristic.
    3. Involvement of the liver, lungs, muscles and heart also occurs.
    4. Although painful and disfiguring, the disease is seldom fatal.

    Nephrogenic systemic fibrosis (NSF) is a rare, progressive, usually fatal disease characterized by skin thickening, painful joint contractures, and fibrosis of multiple organs including the lungs, liver, muscles, and heart. Nearly all documented cases have occurred in patients with chronic severe renal insufficiency who have received gadolinium contrast. Link to Q&A discussion

  7. Which one of the following gadolinium-based contrast agents is less likely than the others to be associated with NSF?
    1. Magnevist®
    2. Dotarem®
    3. OpitMARK™
    4. Omniscan™

    Except for the macrocyclic agent Dotarem®, the other three agents are all linear in structure and have been associated with the greatest number of reported cases of NSF. These have been classified by the ACR as Group I agents, and are no longer advertised in the US and have been withdrawn from the market in many other countries. Link to Q&A discussion

  8. Which gadolinium-based contrast agents has to date not been associated with any nonconfounded cases of NSF?
    1. Dotarem®
    2. ProHance®
    3. MultiHance®
    4. Eovist®

    No cases of NSF have been reported with the newest gadolinium agent, Eovist® (gadoxetate). However, Eovist® is primarily intended for hepatic imaging and thus there is only limited worldwide experience with it compared to the more general purpose agents. Furthermore, Eovist® (and any future new contrast agents) are being given in an “NSF-conscious” era, where high doses of gadolinium are avoided and careful scrutiny of renal function is undertaken prior to contrast administration. Link to Q&A discussion

  9. Below what level of glomerular filtration rate (GFR) does the American Kidney Foundation consider Stage 3 (moderately reduced function) kidney disease?
    1. 90 mL/min/1.73 m²
    2. 60 mL/min/1.73 m²
    3. 30 mL/min/1.73 m²
    4. 15 mL/min/1.73 m²

    Stage 3 chronic kidney disease is generally diagnosed for GFRs in the range of 30-60 mL/min/1.73 m². This is about half the normal kidney function level of 90 mL/min/1.73 m². Link to Q&A discussion

  10. Which one of the following statements about the use of gadolinium in neonates and infants is false?
    1. The half-life of gadolinium contrast in a normal newborn is at least 4 times longer than in an adult.
    2. The per kilogram dose of contrast should be lower than that in adults.
    3. Neonates have a lower renal excretion rate of gadolinium contrast than adults.
    4. No cases of NSF in neonates or infants have been reported.

    Renal excretion rates aside, neonates have twice the volume of extracellular fluid than adults have in proportion to their body weights. Therefore, neonates and young infants who receive gadolinium contrast on a dose-per-kilogram basis will have blood gadolinium concentrations of only one-half that in adults after equilibration. This fact argues against using a lower dose per kilogram in infants than in adults, even though the serum half-life is prolonged. Clinical experience by our group and others has demonstrated that the adult dose of gadolinium contrast (0.1 mmol/kg for most extracellular agents) is also appropriate in infants and children. Link to Q&A discussion

  11. Concerning the administration of gadolinium contrast to lactating women, which statement is false?
    1. Peak excretion into breast milk occurs at about 50 minutes after injection.
    2. Only a tiny fraction (0.01%-0.04%) of the administered dose is excreted in breast milk.
    3. Only 1% of orally ingested contrast gadolinium contrast is absorbed by the infant.
    4. Current scientific evidence shows that breast feeding must be avoided for at least 24 hrs.

    Because (b) and (c) are true, the dose entering the infant's circulation is extremely small (1/1,000,000 of the maternal dose) and the potential toxic effects are thought to be miniscule. Only out of an abundance of safety, many centers recommend (but do not require) suspending breast feeding for 24 hours after a gadolinium-enhanced MR study. Link to Q&A discussion

  12. Concerning the administration of gadolinium contrast during pregnancy, which statement is false?
    1. An increased number of congenital malformations have been observed in infants of mothers receiving gadolinium contrast during pregnancy.
    2. Gadolinium contrast easily passes through the placenta and into the fetal circulation.
    3. Gadolinium contrast absorbed by the fetus is excreted into the urine and subsequently into the amniotic fluid.
    4. Some gadolinium contrast in the amniotic fluid will be swallowed and resorbed through the fetal GI tract.

    In the only controlled human study to date of MRI and gadolinium exposure in pregnancy, a slightly higher incidence of stillbirths and early neonatal deaths (but not congenital malformations) was observed in the gadolinium-exposed group. More worrisome, however, was an increased number of rheumatologic, inflammatory, and infiltrative skin conditions, including some resembling nephrogenic systemic fibrosis (NSF). Link to Q&A discussion

  13. Which of the following statements concerning gadolinium deposition in the brain is false?
    1. Accumulation occurs primarily in the basal ganglia, brainstem, and dentate nuclei.
    2. Several exposures are usually necessary before visible changes are seen.
    3. Changes are most visible on T2*-weighted images.
    4. The incidence of accumulation is less with macrocyclic contrast agents than linear ones.

    All are true except (b). High signal due to accumulated gadolinium is noted on T1-weighted images. Link to Q&A discussion

  14. Concerning “gadolinium deposition disease” which statement is false?
    1. The FDA has determined there is no convincing current evidence for this diagnosis.
    2. One important piece of clinical evidence for it is the increased incidence of Parkinson’s disease in patients receiving gadolinium contrast.
    3. No tissue injury or morphologic changes in gadolinium-accumulating brain areas can be detected by microscopy.
    4. Celebrity Chuck Norris withdrew his lawsuit against Bracco where he claimed they “poisoned” his wife with gadolinium.

    The incidence of Parkinson’s disease is not increased in patients who received gadolinium contrast. Link to Q&A discussion

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Paramagnetic Blood Products

  1. How many iron atoms are in a hemoglobin molecule?
    1. 1
    2. 2
    3. 3
    4. 4

    Hemoglobin is comprised of four subunits, each containing a heme group with an iron (Fe) atom nestled at its center. Link to Q&A discussion

  2. How many sites on each heme group are available for binding oxygen or another small molecule?
    1. 1
    2. 2
    3. 3
    4. 4

    The Fe center of each heme group has 6 potential coordination sites, four of which are occupied by porphyrin nitrogens (N). The fifth coordination site (below the plane of the ring) covalently bonds with a histidine (His) residue from the F8 position of its respective globin chain. This leaves one free coordination site to which oxygen and other small molecules may transiently bind. Link to Q&A discussion

  3. TEXTFORquestion3
    1. Oxyhemoglobin → Deoxyhemoglobin → Methemoglobin → Ferritin
    2. Deoxyhemoglobin → Oxyhemoglobin → Methemoglobin → Ferritin
    3. Oxyhemoglobin → Methemoglobin → Deoxyhemoglobin → Ferritin
    4. Oxyhemoglobin → Deoxyhemoglobin → Ferritin → Methemoglobin

    Answer (b) shows the correct order. Link to Q&A discussion

  4. Which one of the hemoglobin derivatives listed below is diamagnetic?
    1. Oxyhemoglobin
    2. Deoxyhemoglobin
    3. Methemoglobin
    4. Ferritin

    Oxyhemoglobin has no unpaired electrons and is therefore diamagnetic. Link to Q&A discussion

  5. In arterial blood from a healthy patient, what is the expected proportion of deoxyhemoglobin?
    1. 0 %
    2. Less than 5%
    3. 10 – 20 %
    4. Greater than 25 %

    In arterial blood, the fraction of oxyhemoglobin is about 95%, while deoxyhemoglobin constitutes less than 5% (but not zero). A tiny amount of methemoglobin (<< 1%) may also be detected. Link to Q&A discussion

  6. In venous blood from a healthy patient, what is the expected proportion of deoxyhemoglobin?
    1. 0 %
    2. Less than 5%
    3. 10 – 20 %
    4. Greater than 25 %

    In venous blood, oxy-Hb still predominates, though in a smaller ratio (venous oxy:deoxy ≈ 70:30.) Link to Q&A discussion

  7. Which of the following effects on the MR signal does not result from local increased hematocrit during blood clotting?
    1. Decreased free water content, reducing T1, T2, and spin density.
    2. Decreased extracellular space, restricting diffusion.
    3. Increased concentration of phospholipids in red blood cell membranes, shortening T1.
    4. Increased concentration of hemoglobin, potentiating T2/T2* effects as transition to deoxy-hemoglobin occurs.

    All are true except (c). Phospholipid cell membranes have ultrashort T2 values and do not generate a fatty signal on MRI. Link to Q&A discussion

  8. Which of the following imaging findings at 1.5T would not be expected to be seen in a hyperacute (< 12 hrs old) cerebral hematoma?
    1. Restricted diffusion
    2. T1 signal isointense to brain
    3. T2 signal moderately hypointense to brain
    4. At least a rim of hypointensity on GRE/SWI images

    In a hyperacute hematoma, oxyhemoglobin still predominates, except perhaps at the periphery, and the imaging findings suggest a relatively high-water content lesion that is moderately hyperintense on T2-weighted images. Link to Q&A discussion

  9. Which of the following imaging findings at 1.5T would not be expected to be seen in an acute (12–48 hrs old) cerebral hematoma?
    1. Restricted diffusion
    2. T1 signal hyperintense to brain
    3. T2 signal markedly hypointense to brain
    4. GRE/SWI images hypointense to brain

    This phase of hematoma formation is dominated by intracellular deoxyhemoglobin, which shortens T2/T2* significantly. The hematoma becomes markedly hypointense on T2-weighted images. Link to Q&A discussion

  10. Which of the following imaging findings at 1.5T would not be expected to be seen in an early subacute (2 days – 1 week old) cerebral hematoma?
    1. Restricted diffusion
    2. T1 signal hyperintense to brain
    3. T2 signal hyperintense to brain
    4. GRE/SWI images hypointense to brain

    This is the phase of hematoma formation where intracellular methemoglobin predominates. This hemoglobin derivative is highly paramagnetic. Because it is still contained within red blood cells, T2/T2* shortening effects still occur, so T2 signal is low, not high. Access of water molecules close to the iron center due to a conformational change in the globin moiety result in T1 shortening and a bright T1 signal. Link to Q&A discussion

  11. Which of the following imaging findings at 1.5T would not be expected to be seen in a late subacute (1 week – 2 months old) cerebral hematoma?
    1. Minimal to no restricted diffusion
    2. T1 signal hypointense to brain
    3. T2 signal hyperintense to brain
    4. GRE/SWI images show central hyperintensity

    This phase of hematoma formation is dominated by extracellular methemoglobin, released from red blood cells that have ruptured. Methemoglobin is no longer concentrated into multiple intracellular compartments, but becomes uniformly dispersed throughout the hematoma cavity that is now bright on both T1- and T2-weighted images. Link to Q&A discussion

  12. Which of the following imaging findings at 1.5T would not be expected to be seen in the center of a chronic (> 2 months old) cerebral hematoma?
    1. Minimal to no restricted diffusion
    2. T1 signal hypointense to brain
    3. T2 signal hyperintense to brain
    4. GRE/SWI central hypointensity to brain

    The imaging characteristics of the center of a chronic hematoma reflects its high water content. As such this region is typically hyperintense to brain on T2-weighted images and hypointense on T1-weighted images with no or minimally restricted diffusion. GRE/SWI signal centrally is also high, but may be dark along the rim of the hematoma cavity due to ferritin/hemosiderin deposition. Link to Q&A discussion

  13. Which of the following statements about ferritin is incorrect?
    1. It is the principal iron storage molecule found in animal cells.
    2. It consists of a hollow protein shell into which iron atoms are packed.
    3. A typical ferritin molecule contains about 2000 iron atoms.
    4. It is ferromagnetic.

    The ferritin core acts as a solid piece of metal with a single magnetic domain, exhibiting superparamagnetism. Ferromagnetic materials, by contrast, consist of multiple erritinhemosiderin.html domains and retain some residual magnetization after an external magnetic field is removed. Link to Q&A discussion

  14. Concerning ferritin and hemosiderin, which statement is true?
    1. The iron in hemosiderin is insoluble; the iron in ferritin is soluble.
    2. Both are visible by light microscopy.
    3. Ferritin is paramagnetic, but hemosiderin is ferromagnetic.
    4. Both hemosiderin and ferritin have a fixed structure and composition.

    Only (a) is true. Ferritin is much smaller than hemosiderin and can only be visualized at electron microscopy. Both are paramagnetic. Ferritin has a fixed structure and composition; hemosiderin is an amorphous conglomeration of ferritin particles, proteins, and lipids. Link to Q&A discussion

  15. Which of the following processes does not affect the appearance of subarachnoid hemorrhage (SAH) as compared to intraparenchymal brain hemorrhage?
    1. SAH clots are small.
    2. SAH clots are readily dispersed.
    3. SAH mixes with cerebrospinal fluid.
    4. Ambient oxygen levels in the subarachnoid space are low, resulting in faster aging of the hematoma.

    Only (d) is false. Ambient oxygen levels in the subarachnoid space are high, resulting in slower aging of the hematoma. For example, methemoglobin formation is rare until at least 1 week after ictus. Link to Q&A discussion

  16. Concerning CT and MRI of subarachnoid hemorrhage (SAH), which statement is false?
    1. Acute SAH is better seen on CT than on MRI.
    2. The best MR sequence for identifying acute SAH is T1-FLAIR.
    3. Subacute SAH may be better seen on MRI than CT.
    4. Evidence for remote SAH is much better seen on MRI than CT.

    Option (b) is false. The best sequences for identifying SAH on MRI are T2-FLAIR, GRE/SWI, and DWI. Link to Q&A discussion

  17. Which of the following statements concerning the appearance of hemorrhage at very low fields (<0.15 T) is true?
    1. Intracellular deoxyhemoglobin is noticeably dark on T2-weighted images.
    2. Intracellular methemoglobin is noticeably dark on T2-weighted images.
    3. Extracellular methemoglobin is bright on T1-weighted images.
    4. The center of a hyperacute hematoma is dark on T1-weighted images.

    Only (c) is true. Neither intracellular deoxy- and met-Hb are dark on T2 weighted images as they are at high fields. This is because the dephasing is due to susceptibility which scales with the square of the magnetic field. The center of an acute clot is bright on T1-weighted images due to hemoconcentration and protein effect. Link to Q&A discussion

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