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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

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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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7

8

9

10

11

12

1

2

3 5

613

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15

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Apical Mid Basal

Short Axis

LAD RCA LCX

4

7

8

9

10

11

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1

2

3 5

613

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15

16

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