ASMIRT – MRI Accreditation Exam
With Questions And Answers Updated
2026/2027|Graded A+
What is a MIP and why is it used in MRA? - ANSWER>This technique is routinely used to reformat MRA
images. The stack of 2D or 3D slices is treated as a volume of data which can be projected in any
orientation as a 2D map of the highest intensity pixels. This separates out the vessels and allows them to
be displayed at the orientation most appropriate to their anatomical position. It is also possible to
combine a series of images at incremental projection angles into a cine loop to give a 3 dimensional
perception of the vascular anatomy.
What is the molecular make-up of Gadolinium? - ANSWER>Gadolinium, the paramagnetic ion used in
MR contrast agents, has 7 unpaired electrons which gives rise to a large magnetic moment and makes it
the most efficient proton relaxation enhancer.
Why is gadolinium not suitable for use as a contrast agent in its free ionic form? - ANSWER>In its free
ionic form, Gadolinium is not suitable for use as a contrast agent because:
• it is toxic
,• it forms insoluble salts which are taken up by the liver
How can the molecular make up of Gadolinium be altered to make it safe for contrast administration? -
ANSWER>It needs to be bound to a carrier molecule called a ligand to produce a combined molecule
called a chelate. eg:
• Gd plus DTPA = Gd-DTPA or gadopentetate (Magnevist)
• Gd plus DTPA-BMA = Gd-DTPA-BMA or gadodiamide - a non-ionic derivative (Omniscan)
What affect does contrast have on T1 and T2 relaxation times? - ANSWER>T1 relaxation is facilitated by
fluctuating magnetic fields such as those produced by the tumbling motion of neighbouring molecules
(dipole-dipole interactions). Molecules the size of fat tumble and therefore produce field fluctuations at
a frequency near the Larmor frequency which will provide the most efficient T1 relaxation. Normally,
water molecules tumble too rapidly for efficient relaxation. If a tumbling molecule with a large magnetic
moment (i.e. Gadolinium) is placed in the presence of water protons, local field fluctuations will be
created with a substantial component at or near the Larmor frequency - so T1 relaxation will be
enhanced. Both T1 and T2 relaxation times are shortened although the effect is much more pronounced
for T1.
, What enhances in a brain scan following contrast administration? - ANSWER>• Areas of hyper-vascularity
- eg scar tissue
• Vessels - contrast enhanced MRA
• Blood brain barrier :
• Extra-axial areas outside the BBB such as the falx, pituitary and choroid plexus will enhance.
• With an intact BBB, intra-axial areas will not enhance. Disruption of the BBB will allow accumulation of
gadolinium in lesions such as neoplasms, infarcts and abscesses
What is the standard dose for GBCA? - ANSWER>Standard dose is 0.1 mmol/kg (.2ml/kg) Maximum dose
= triple dose = 0.3mmol/kg
What is the toxicity of GBCA? - ANSWER>Low toxicity Min lethal dose for rats and mice > 200 x patient
imaging dose
What is the excretion pathway of GBCA? - ANSWER>80% via kidneys in 3 hours 95% via kidneys in 24
hours 98% via feces and urine in one week
With Questions And Answers Updated
2026/2027|Graded A+
What is a MIP and why is it used in MRA? - ANSWER>This technique is routinely used to reformat MRA
images. The stack of 2D or 3D slices is treated as a volume of data which can be projected in any
orientation as a 2D map of the highest intensity pixels. This separates out the vessels and allows them to
be displayed at the orientation most appropriate to their anatomical position. It is also possible to
combine a series of images at incremental projection angles into a cine loop to give a 3 dimensional
perception of the vascular anatomy.
What is the molecular make-up of Gadolinium? - ANSWER>Gadolinium, the paramagnetic ion used in
MR contrast agents, has 7 unpaired electrons which gives rise to a large magnetic moment and makes it
the most efficient proton relaxation enhancer.
Why is gadolinium not suitable for use as a contrast agent in its free ionic form? - ANSWER>In its free
ionic form, Gadolinium is not suitable for use as a contrast agent because:
• it is toxic
,• it forms insoluble salts which are taken up by the liver
How can the molecular make up of Gadolinium be altered to make it safe for contrast administration? -
ANSWER>It needs to be bound to a carrier molecule called a ligand to produce a combined molecule
called a chelate. eg:
• Gd plus DTPA = Gd-DTPA or gadopentetate (Magnevist)
• Gd plus DTPA-BMA = Gd-DTPA-BMA or gadodiamide - a non-ionic derivative (Omniscan)
What affect does contrast have on T1 and T2 relaxation times? - ANSWER>T1 relaxation is facilitated by
fluctuating magnetic fields such as those produced by the tumbling motion of neighbouring molecules
(dipole-dipole interactions). Molecules the size of fat tumble and therefore produce field fluctuations at
a frequency near the Larmor frequency which will provide the most efficient T1 relaxation. Normally,
water molecules tumble too rapidly for efficient relaxation. If a tumbling molecule with a large magnetic
moment (i.e. Gadolinium) is placed in the presence of water protons, local field fluctuations will be
created with a substantial component at or near the Larmor frequency - so T1 relaxation will be
enhanced. Both T1 and T2 relaxation times are shortened although the effect is much more pronounced
for T1.
, What enhances in a brain scan following contrast administration? - ANSWER>• Areas of hyper-vascularity
- eg scar tissue
• Vessels - contrast enhanced MRA
• Blood brain barrier :
• Extra-axial areas outside the BBB such as the falx, pituitary and choroid plexus will enhance.
• With an intact BBB, intra-axial areas will not enhance. Disruption of the BBB will allow accumulation of
gadolinium in lesions such as neoplasms, infarcts and abscesses
What is the standard dose for GBCA? - ANSWER>Standard dose is 0.1 mmol/kg (.2ml/kg) Maximum dose
= triple dose = 0.3mmol/kg
What is the toxicity of GBCA? - ANSWER>Low toxicity Min lethal dose for rats and mice > 200 x patient
imaging dose
What is the excretion pathway of GBCA? - ANSWER>80% via kidneys in 3 hours 95% via kidneys in 24
hours 98% via feces and urine in one week
