Adquisicion Reconstruccion RM Parte 1
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Transcript of Adquisicion Reconstruccion RM Parte 1
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Adquisición y reconstrucción de imágenes con resonancia magnética
Pablo IrarrázavalDirector
Centro de Imágenes BiomédicasPontificia Universidad Católica de Chile
Taller
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Unidades1. Fundamentos de Resonancia Magnética.2. Repaso de la teoría del muestreo y análisis de
frecuencia.3. Estrategias de muestreo y reconstrucción en
RM
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FUNDAMENTOS DE RESONANCIA MAGENÉTICA
Unidad 1
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Tópicos• Imágenes médicas– Rayos X– Medicina Nuclear– Ultrasonido– MRI
• MRI hoy• Principios de MRI• Reconstrucción• Tendencias
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Mirada histórica
Rayos X
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Wilhelm Conrad RöntgenPremio Nobel 1901
Rayos X
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Tubo Crookes, 8 Nov. 1895, Roentgen
Mano de Bera Roentgen, 22 Dic. 1895
Rayos X
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Rayos X: Ondas Electromagnéticas
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Semi-transparencia del cuerpo
Se usan longitudes de onda de0,5 A (25 kev) a 0,01 A (1 Mev)
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Modalidades para imágenes médicas
Rayos X - Radiografías
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Radiografía moderna
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Rayos X: CAT
Diagrama de Hounsfield
Primer prototipo
Sir Godfrey Newbold HounsfieldPremio Nobel 1979
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Modalidades para imágenes médicasRayos X - Tomografia axial computarizada (TAC o CT)
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CT moderno
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Mirada histórica
Medicina Nuclear
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Medicina Nuclear
Glenn T. SeaborgPremio Nobel 1951
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Medicina Nuclear
Georg von HeveseyPremio Nobel 1943Experimentó en plantas con radioisótopos
Ernest O. LawrencePremio Nobel 1939Inventó ciclotrón
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Medicina Nuclear: Rayos Gama• Rayos Gama son ondas electromagnéticas
indistinguibles de los rayos X• Frecuencia: 25 a 1000 kev• Se producen en el núcleo del átomo
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Modalidades para imágenes médicas
Medicina Nuclear (Rayos γ) - SPECT
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SPECT
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Modalidades para imágenes médicas
Medicina Nuclear (Rayos γ) - PET
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PET
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Mirada histórica
Ultrasonido
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Ultrasonido
Jean-Daniel Colladen, 1826Velocidad del sonido en agua (1435 m/s)
Lazzaro Spallanzani, 1794Descubrió ultrasonido en murciélagos
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Ultrasonido
Paul Langevinhidrofono: primer sonar práctico, 1915
Instrumentos Ultrasonido,Floyd Firestone, EEUUDonald Sproule, InglaterraAdolf Trost, Alemania
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Ultrasonido: ondas de presión
Velocidad en agua: 1500 m/s (atenuación media)
Velocidad en aire: 340 m/s (atenuación alta)Velocidad en hueso: 2300 m/s (poca
atenuación)
Frecuencias: 1 a 20 MHz
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Modalidades para imágenes médicas
Ultrasonido
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Ultrasonido
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Mirada histórica
MRI
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Sobre los hombros de gigantes
"for his resonance method for recording the magnetic properties of atomic nuclei"
Nobel 1944Isidor Isaac Rabi
"for his contribution to the development of the molecular ray method and his discovery of the magnetic moment of the proton"
Nobel 1943Otto Stern
Pictures: Nobelprizes.org
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Sobre los hombros de gigantes
Felix Bloch
"for their development of new methods for nuclear magnetic precision measurements and discoveries in connection therewith"
1952 Nobel Edward Mills Purcell
Pictures: Nobelprizes.org
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Sobre los hombros de gigantes
"for his contributions to the development of the of high resolution nuclear magnetic resonance (NMR) spectroscopy"
1991 Nobel Richard R. Ernst
2002 Nobel Kurt Wüthrich
"for his development of nuclear magnetic resonance spectroscopy for determining the three-dimensional structure of biological macromolecules in solution"
Pictures: Nobelprizes.org
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Sobre los hombros de gigantes
Sir Peter Mansfield
"for their discoveries concerning magnetic resonance imaging"
2003 Nobel Paul C. Lauterbur
Pictures: Nobelprizes.org
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Primera imagen, Lauterbur 1973
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Resonador de Mallard 1974
University of Aberdeen(first spin-warp image)
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Resonador e imagen de Damadian1974
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MRI hoy
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Siemens
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Philips
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General Electric
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Imágenes neuronales
3T
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Campos visuales extendidos
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Mamas y abdomen
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Cardíaca
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FunctionAngiografía
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Función• Espectroscopía
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MRI
Principios
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• La materia puede presentar la propiedad de magnetismo
• Un imán produce una magnetización (cada protón en el núcleo es como un pequeño imán)
• Átomos tienen una carga magnética intrínseca (núcleos)
• Átomo (cargado magnéticamente) girando = spin
Magnetismo
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Frecuencia de Larmor• En presencia de un campo magnético B, un spin magnético
tiene una frecuencia de resonancia
hidrógeno = 42.58 MHz/T
es la frecuencia de Larmor (resonancia) y es proporcional al campo magnético B
es la frecuencia a la que un spin gira bajo la acción de un campo magnético B
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Nuclii spin sensitivity 2z/T)1H 1/2 1.000 42.5813C 1/2 0.016 10.7119F 1/2 0.870 40.0531P 1/2 0.093 11.26
Picture: magnet.caltech.edu/mri/mri-100
Spins y momentos
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Resumen de las etapas• Polarización (entrando en el magneto)• Excitación (radiación RF en el cuerpo)• Lectura (inducción en las bobinas, ecuación de
señal)• Reconstrucción (transformada de Fourier
inversa)
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v01 55
Polarización ReconstrucciónExcitación Lectura
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Polarización ReconstrucciónExcitación Lectura
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Polarización ReconstrucciónExcitación Lectura
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Polarización ReconstrucciónExcitación Lectura
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Polarización ReconstrucciónExcitación Lectura
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Polarización ReconstrucciónExcitación Lectura
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Polarización ReconstrucciónExcitación Lectura
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Polarización ReconstrucciónExcitación Lectura
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Polarización ReconstrucciónExcitación Lectura
Espacio-k Imagen
IFFT
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Ecuación de Bloch
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Ecuación de Bloch
Spins precess around B0 at the Larmor frequency:
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0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
t [s]
Mx
y
T2 = 100 ms
“spin-spin” relaxation T2
Ecuación de Bloch
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0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
t [s]
Mz
0 0.2 0.4 0.6 0.8 10
0.2
0.4
0.6
0.8
1
t [s]
Mz
T1 = 200 ms
“spin-lattice” relaxation T1
Ecuación de Bloch
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Magnetic gradients
Sin distorsiones en el campo
Ecuación de Bloch
Picture: Laboratoire Kastler Brossel
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Ecuación de señal
Ignorando la relajación T2 y demodulando a 0
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Ecuación de señal
Donde es la transformada de Fourier de
k-space
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Tendencias en MRI
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Tamaño y forma• Equipos más cortos
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Tamaño y forma• Cerrados versus abiertos
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Tamaño y forma• Grandes versus pequeños
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Campo• Bajo versus alto campo
0.23 T 8 T
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Function• functional MRI
Picture: HITlab
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Function• Interventional MRI
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Finalmente, Costo• For superconducting magnets (US dollars)
• Faster growing modality
0.5T 1T 1.5T 3T
Year 2000 600k 1200k 1800k
Year 2006 100k 800k 1100k 1800k