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Strahlenschutz durch alternative Bildgebungsverfahren –MRT
3. Berliner Strahlenschutzseminar26. April 2012
Bernhard SchnackenburgSenior Clinical Scientist2012
• Einleitung/Sicherheit im MRT
• Technische Entwicklungen
• Diagnostik koronarer Herzerkrankungen
• Diagnostik angeborener Herzfehler
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Patienttable
RF shield
RF coil
RF coil RF transmitter
RF receiver
magnet
magnet
cooling
gradient coils
gradient coils
X-gradient
Y-gradient
Z-gradient
computer
Wasserstoff-atomkerne
Patienttable
RF coil
RF coil
magnet
magnet
gradient coils
gradient coils
B0
1. Gradienten ein + HF-Puls senden
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Patienttable
RF coil
RF coil
magnet
magnet
gradient coils
gradient coils
B0
2. Gradienten ein + HF-Signal empfangen
3. Bild berechnen
Bildk-RaumAnaloge Signale (Echos)
[m][1/m](Orts)frequenz
FT
Signaledigitalisieren
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water image (H2O) fat image (CH2)
Sicherheit
- Reversible Effekte (EKG-Verzerrungen, Schwindel, Magneto-Phosphene)- Ferromagnetische Materialien werden angezogen
Statisches Magnetfeld (B ≤ 4T)
- Reversible Effekte (Stimulation von peripheren Nerven)- Schallemission (Hörschutz obligatorisch)
Gradientenfelder (Schwellwerte für dB/dt in abh. von der Schaltzeit)
- Reversible Effekte (Erwärmung, ≤ 1°C Körperkerntemperatur-Erhöhung)- Erwärmung von Implantaten möglich
Hochfrequenzfeld (SAR* ≤ 4 W/kg)
*SAR = specific absorbtion rate
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Technische Entwicklungen
Klassisches Design
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Panorama 1Tesla
60 cm 70 cm
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Field strength
Bernhard Schnackenburg, 01/2007 14
SN
R
field strength Wav
elen
gth
insi
de th
e bo
dy
For homogeneous rf- excitation: object must be smaller than wavelength
Higher field strength: benefits and challenges
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Standing waves @ 3T
Simulation (3.0T)
Reality (3.0T)
Torso
Spine, cardiac, brain …
dielectric shading
Dielectric shading (3T)
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Parallel RF transmission @ 3T
The RF Shimming (B1 calibration) Procedure
Survey
B1 calibration(1 slice)
B1 Map
B1 ShimTool
Scanning withMultiTransmit
1. pLA2. …………………
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Patient adaptive RF shimming
Note: BSA = Body Surface Area
ISMRM 2011 #3353 Krishnamurthy et al.
ADC
Phased Array Spulen (ADC in der Spule)
SNR
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Kardio MRT
Cardiovascular MRI: Indications/methods
• Coronary artery disease: ischemia, viability
• Heart valve disease
• Congenital heart disease
• Cardiomyopathies
• Pericardial disease
• Tumors, thrombi and masses
• MR – angiography
• MR – spectroscopy
• MR – guided cardiovascular interventions
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Kurzachse (SA) Vierkammerblick (4Ch)
Zweikammerblick (2Ch) Dreikammerblick (3Ch)
Darstellung des Herzens
Motion
RespirationBeating of the heart
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Diagnostik koronarer Herzerkrankungen
(Ischämiediagnostik)
Bernhard Schnackenburg IACSM 2010
...... In summary, documentation of ischaemia using functional
testing is strongly recommended before elective invasive
procedures, preferably using non-invasive testing before invasive
angiography.
5. Strategies for pre-intervention diagnosis and imaging
Cardiovascular magnetic resonance and singlephoton emission computed tomography for
diagnosis of coronary heart disease (CE-MARC): a prospective trial
Greenwood JP et al, LANCET December 2011
� CMR sensitivity 86.5 % vs. SPECT sensitivity 66.5 %
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Perfusion abnormality
Diastolic dysfunction
Systolic dysfunction
ECG alterations
Chest pain
Myocardial infarction
Metabolic alterations
Duration of ischemia
Courtesy: Ingo Paetsch, Cosima Jahnke
Ischämie Kaskade
Time
PerfusionMethods:• First pass of a CA(T1-effect)
• Sequential measurementof several slices/heart-beat (at least 3 slices)
• Single shot technique
• spatial resolution: < 3 x 3 x 8 mm
• Rest and stress (Adenosin)i. e. heart rate up to 120 bpm
n
Short Axis
LAD RCA LCX
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3 5
613
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Apical Mid Basal
Short Axis
LAD RCA LCX
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3 5
613
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Apical Mid Basal
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time
signal
Perfusion (Beurteilung visuell)
Perfusionsdefekt
Sensitivität: 88%Spezifität: 82%Diagnostische Genauigkeit: 85%
CMR-Perfusion during adenosin stress• 65 y/o man with suspected CAD, atypical chest pain
• Arterial hypertension, diabetes, hyperlipidemia
• ergometry inconclusive
High grade stenosis:CX and LAD
Courtesy: DHZ Berlin
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Saturation recovery 3D T1-TFE(patch from ETH Zürich1) )
• 10 x k-t acceleration (effective 6.5)
• k-t SENSE reconstruction (WIP: PCA reconstruction2) )
• TR/TE = 1.85 / 0.74 ms, Flip angle = 15o
• Spatial resolution: 2.30 x 2.30 mm²
• 8 slices with 10 mm (reconstructed to 16 slices with 5 mm)
• Typical FOV: 380 x 380 x 80 mm3
• 30 dynamics
• Breathhold in inspiration (up to 30 s)
• Acquisition window per heart beat: 220 ms
• WET* saturation pulse (120°, 90°, 180°, 230°; delay 150 ms)
• 0.5 molar CA (0.1 mmol/kg/BW, 4 ml/s)
*WET – water suppression enhanced through T1 effects1)Vitanis V et al: MRM 20102)Pedersen H et al: MRM 2009
Saturation recovery 3D T1-TFE (Adenosin stress)
Patient with suspected CAD,atypical chest pain
Courtesy: DHZ Berlin
k-t acceleration: 10; 16 slices2.3 x 2.3 x 5 mm³
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Saturation recovery 3D T1-TFE
Patient with suspected CAD,atypical chest pain
No perfusion defect at rest
Diagnostik angeborener Herzfehler
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Strahlenrisiko bei Kindern
“Importantly, children are at much greater risk than adults from a given dose of radiation both because they are inherently more radiosensitive and because they have more remaining years of life during which a radiationinducedcancer could develop.“
Prakash A et al: Circ Cardiovasc Imaging. 2010;3:112-125
Prakash A et al: Circ Cardiovasc Imaging. 2010;3:112-125
Part 1
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Prakash A et al: Circ Cardiovasc Imaging. 2010;3:112-125
Part 2
Prakash A et al: Circ Cardiovasc Imaging. 2010;3:112-125
Children’s Hospital Boston
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Prakash A et al: Circ Cardiovasc Imaging. 2010;3:112-125
Children’s Hospital Boston
Fortschr Röntgenstr 2012; 184: 345–368
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Bei angeborenen Herzfehlern sind 23 Frage-stellungen aufgeführt:
I1 Zuverlässig einsetzbar und anderen Verfahren überlegenI2 Diagnostische Genauigkeit vergleichbar mit anderen VerfahrenI3 Einsatz technisch möglich und validiert, Indikation aber nur inEinzelfällen gegebenU unklare Indikation, keine oder nicht kongruente Studienergebnisse
MRT
8 x I113 x I22 x I3
CT
0 x I17 x I210 x I36 x U
Fortschr Röntgenstr 2012; 184: 345–368
3D – balanced SSFP (free breathing)
Sørensen T et al: Circulation. 2004;110:163-169
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Transposition of the great arteries
Sørensen T et al: Circulation. 2004;110:163-169
Kinking aortic arch
Sørensen T et al: Circulation. 2004;110:163-169
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Courtesy Dr. Junge, AKK
CINE Imaging (Panorama 1T)
11 year, girlartificial pulmonary valveaneurysm of the RVOT
Quantitative 2D Flow @ 3T
Stroke volume (SV) 86.3 ml
Forward SV 153.1 ml
Backward SV 66.9 ml
Regurgitant Fraction: 43.7 %
insufficiency of theaortic valve
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SVC
AAO
LV
RUPV
ASDIVC
Courtesy Philipp Beerbaum
Vorhofseptumdefekt
ASD
Flussmessung
Ao
PA
Ao
PA
Courtesy Philipp Beerbaum
Planung der Flussmessungen
Aorta
Pulmonalis
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PA
PA = 58.5 ml(range, 57.4-60.1ml)
Ao
Ao = 23.7 ml (range, 23.2-24.6 ml)
Qp/Qs=2.45
PA - Flussvolumen in der PulmonalisAo - Flussvolumen in der Aorta a.
Qp - pulmonalis SchlagvolumenQs - aortales Schlagvolumen
Quantifizierung der Fluss- und Schlagvolumina
Courtesy Philipp BeerbaumRelevanter Links-Rechts-Shunt (Qp/Qs > 1.5)
3D Flow
courtesy: Gerard Crelier, GyroTools LLC
Peak systolic flow through the aortic valves (streamlines).
Helical flow pattern in a patient with dilated ascending aorta (pathlines)
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Coronaries
Coronary anomaly
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Vielen Dankfür IhreAufmerksamkeit