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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