06.12.2018 1 Advanced Imaging Techniques Angiography Prof. Dr. Frank G. Zöllner Computer Assisted Clinical Medicine Medical Faculty Mannheim Heidelberg University Theodor-Kutzer-Ufer 1-3 D-68167 Mannheim, Germany [email protected]www.ma.uni-heidelberg.de/inst/cbtm/ckm Name I Slide 2 I 12/6/2018 Learning Goals introduction to advanced imaging techniques in MR, CT and CBCT basic MRI principles -> Physics of Imaging Techniques Goals: 1. How does the technique work ? 2. What kind of images do we receive? 3. Where is this applied to ? Literature is given in the respective lectures Slides of the lectures at https://www.umm.uni-heidelberg.de/inst/cbtm/ckm/lehre/index.html
Transcript
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Advanced Imaging TechniquesAngiography
Prof. Dr. Frank G. ZöllnerComputer Assisted Clinical MedicineMedical Faculty Mannheim Heidelberg UniversityTheodor-Kutzer-Ufer 1-3D-68167 Mannheim, GermanyFrank.Zoellner@medma.uni-heidelberg.dewww.ma.uni-heidelberg.de/inst/cbtm/ckm
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Learning Goals
introduction to advanced imaging techniques in MR, CT and CBCT basic MRI principles -> Physics of Imaging Techniques
Goals:
1. How does the technique work ?
2. What kind of images do we receive?
3. Where is this applied to ?
Literature is given in the respective lectures Slides of the lectures at
Hölscher et al., Real-time cerebral angiography: sensitivity of a new contrast-specific ultrasound technique. American Journal of Neuroradiology 2007 28(4):635-9
James C. Carr and Timothy J. Carroll, Magnetic ResonanceAngiography: Principles and Applications. Springer, 416 pages
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Angiography
Representation/imaging of the vessels Diseases of the arteries:
Arteriosclerosis and its sequelae Vascular constrictions, e.g. coronary heart disease, carotid
stenosis, peripheral arterial occlusive disease Acute vascular occlusion, e.g. heart attack aneurysm of vessels (aneurysms) vascular injuries vascular malformations
Diseases of the veins: Thromboses varicose veins
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Imaging Techniques for Angiography
X-ray DSA CTA
US
MRI TOF CE-MRA
https://en.wikipedia.org/wiki/Angiography, Hölscher et al. Am J Neurorad 2007
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Digital Substraction Angiography (DSA)
Aim: Visualization of vessel
Question: Are we able to visualize vesselsimply by standard X-ray ?
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X-ray contrast agent
negative contrast media: air, CO2 NO2
positive contrast agents: tri-iodine-benzoin-acid or
similar (vessels) barium sulfate BaSO4
(gastrointestinal)
absorption coefficient for iodine in limb angiography
optimum tube voltage for an iodine contrast medium is at 63 kV
Morneburg. “Bildgebende Systeme für die medizinische Diagnostik” 1995
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Digital Substraction Angiography (DSA)
Iodine-containing contrast medium is injectedinto the patient Via vein access (i.v.) Via catheter (selective angio)
after a waiting period, x-rays are taken today, only digital subtraction angiography
(DSA) with catheter is available
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Comparison – Angiographie / DSA
classic angiography DSA
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Principle of DSA
X-ray wo CA„Mask“
X-ray with CA„Fill“
substractedimage
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Mask Fill Subtraction
CA Signal Time Curve
Morneburg. “Bildgebende Systeme für die medizinische Diagnostik” 1995
time
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Morneburg. “Bildgebende Systeme für die medizinische Diagnostik” 1995
Digital Substraction Angiography (DSA)
console
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Angiography device
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Artis zeego
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maximum 6 images/sec at high dose
Laubenberger and Laubenberger. „Technik der medizinischen Radiologie“, Deutscher Ärzte-Verlag 1999
Pulsed DSA
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fixed mask consisting of several integrated images, reduced vascular pulsations by weighting the images during addition
Laubenberger and Laubenberger. „Technik der medizinischen Radiologie“, Deutscher Ärzte-Verlag 1999
continues DSA
subtraction subtraction
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Pro/cons of DSA technqiues
High frame rates Hardly any pulsations Weighted Images / Mask High radiation exposure High load on the X-ray tube
Lower frame rate High contrast due to individual
pulses Overall radiation exposure
lower Lower tube load
contin. DSA Pulsed DSA
fast processes morphology
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MR Angiography
categorised into contrast-enhanced time-of-flight (TOF) phase-contrast
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CE MR Angiography
widespread acceptance due to their ease of use
ability to quickly, reliably, and robustly produce high-quality diagnostic images of large vascular territories
CE-MRA has replaced X-ray DSA as the method ofchoice for imaging certain vasculature: the carotid and vertebral arteries, the aorta and renal arteries, the vessels of the lower extremities
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CE MR Angiography
achieve signal differences between blood and stationarytissuesmagnitude of the magnetization from moving blood is
larger than the magnitude of the magnetization fromstationary tissues
injecting a contrast material intravenously to selectivelyshorten the T1 of the blood
T1-weighted imaging method, appropriatelysynchronized to acquire data during the fi rst pass ofthe contrast material through the arteries of interest
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CE MR Angiography
A coronal MIP image of thevessels of the thighs of a healthy volunteer acquiredusing a coronal 3D contrast-enhanced MRA acquisitionmethod applied after intravenous injection of a gadolinium-based contrastmaterial
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CE MR Angiography
Injection rates typically range from 0.5 to 4.0 ml/s for CE-MRA.
Injection volumes range from 0.1 to 0.3 mmol of contrastmaterial per kg of patient body weight (mmol/kg)
typical values in the range of 20–40 ml of contrast material
reduce the T1 of blood to as low as 50 ms during the firstpass of the contrast material
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CE MR Angiography
Sequences fast 3D gradient echo recall sequences with RF spoiling Time-resolved 2D /3D T1-weighted image acquisition (similar to
perfusion MRI)
for fast GRE synchronisation of the bolus arrival into the vesselterritory is important
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CE MR Angiography
Sequences fast 3D gradient echo recall sequences with RF spoiling Time-resolved 2D /3D T1-weighted image acquisition (similar to
perfusion MRI)
for time resolved images fast repeated imaging is needed
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Time-of-Flight (TOF) MR Angiography
TOF techniques derive contrast between flowing bloodand stationary tissues by manipulating the magnitude ofthe magnetization, such that the magnetization is large formoving blood and small for stationary tissues
do not require the injection of a contrast material
TOF MRA techniques rely on the fact that blood is in motion, and stationary tissues are not
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TOF MR Angiography
a spoiled, fast gradient-echo sequence 2D: thin slices are imaged 3D: thin slabs are imaged and the slabs are encoded into slices
using a phase-encoding method signal decreases with
increasing number of RF pulsesexperienced
the equilibrium signal is larger for tissues with shorter T1
Time sequnce so that TR isintermediate long: high signal for flowing blood low signal for stationary tissue
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TOF MR Angiography
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TOF effects in the presence of plug flow with speed v in direction z : when the velocity is higher than the critical velocity as given, spins
in the blood region I experience only one RF pulse and then exitthe imaging slice before the next RF application.
Spins in region II are not affected by the first excitation but by thenext RF pulse
when the blood is moving slower than the critical velocity, thesaturation effect can be understood by dividing the slice intomultiple segments.
Blood located in each segment experiences a different number ofRF pulses, RF( n ), resulting in different saturation effectsdepending on n
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TOF MR Angiography
2D TOF lower extremities
3D TOF brain
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Phase Contrast MR Angiography
PC MRA methods provide a direct quantitative measure of the velocityof the flowing blood
can be acquired using 2D or 3D acquisitions derive contrast between flowing blood and stationary tissues by
manipulating the phase of the magnetization phase of the magnetization is zero for stationary tissues and non-zero for moving tissues
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Phase Contrast MR Angiography
timing diagram for a 2D phase-contrast MRA pulse sequence bipolar flow-encoding gradient on the frequency encoding axis
remember: diffuions encoding gradients !
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Phase Contrast MR Angiography
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Phase Contrast MR Angiography
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Phase Contrast MR Angiography
Magnitude image: the signal intensity represents the MR signal amplitude averaged
over the two scans used for one-dimensional velocity encoding. Complex difference image (flow encoded magnitude image):
the signal intensity represents the absolute value of the phaseshift
contains no information about the flow direction (e.g., phase shiftsof −170°and +170°shows the same pixel intensity)
Phase difference image: the signal intensity represents the phase angle ∆ࢶ between the
reference and the motion encoded scan, i.e., the local velocitiesalong the encoding direction.
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Phase Contrast MR Angiography
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Phase Contrast MR Angiography
velocity sensitivity “venc ” refers to the maximum velocity that can beencoded by the bipolar gradient
