RESUMEN
A recently developed compact 3 T (C3T) MRI scanner with high performance gradients [1, 2] has a dedicated radiofrequency (RF) transmit coil that exposes only the head, neck and a small portion of the upper body region during head-first scanning. Due to the unique coil geometry and patient positioning, the established SAR model used for a conventional whole-body scanner cannot be directly translated to the C3T. Here a specific absorption rate (SAR) estimation and validation framework was developed and used to implement a dedicated and accurate SAR prediction model for the C3T. Two different SAR prediction models for the C3T were defined and evaluated: one based on an anatomically derived exposed mass, and one using a fixed anatomical position located caudally to the RF coil to determine the exposed mass. After coil modeling and virtual human body simulation, the designed SAR prediction model was implemented on the C3T and verified with calorimetry and in vivo scan power monitoring. The fixed-demarcation exposed mass model was selected as appropriate exposed mass region to accurately estimate the SAR deposition in the patient on the C3T.
Asunto(s)
Imagen por Resonancia Magnética , Ondas de Radio , Simulación por Computador , Humanos , Posicionamiento del Paciente , Fantasmas de ImagenRESUMEN
The major breast cancer suppressor proteins BRCA1 and BRCA2 play essential roles in homologous recombination (HR)-mediated DNA repair, which is thought to be critical for tumor suppression. The two BRCA proteins are linked by a third tumor suppressor, PALB2, in the HR pathway. While truncating mutations in these genes are generally pathogenic, interpretation of missense variants remains a challenge. To date, patient-derived missense variants that disrupt PALB2 binding have been identified in BRCA1 and BRCA2; however, there has not been sufficient evidence to prove their pathogenicity in humans, and no variants in PALB2 that disrupt either its BRCA1 or BRCA2 binding have been reported. Here we report on the identification of a novel PALB2 variant, c.104T>C (p.L35P), that segregates in a family with a strong history of breast cancer. Functional analyses showed that L35P abrogates the PALB2-BRCA1 interaction and completely disables its abilities to promote HR and confer resistance to platinum salts and PARP inhibitors. Whole-exome sequencing of a breast cancer from a c.104T>C carrier revealed a second, somatic, truncating mutation affecting PALB2, and the tumor displays hallmark genomic features of tumors with BRCA mutations and HR defects, cementing the pathogenicity of L35P. Parallel analyses of other germline variants in the PALB2 N-terminal BRCA1-binding domain identified multiple variants that affect HR function to varying degrees, suggesting their possible contribution to cancer development. Our findings establish L35P as the first pathogenic missense mutation in PALB2 and directly demonstrate the requirement of the PALB2-BRCA1 interaction for breast cancer suppression.
Asunto(s)
Proteína BRCA1/metabolismo , Neoplasias de la Mama/metabolismo , Proteínas Nucleares/metabolismo , Proteínas Supresoras de Tumor/metabolismo , Secuencia de Aminoácidos , Proteína BRCA1/genética , Neoplasias de la Mama/genética , Neoplasias de la Mama/patología , Línea Celular Tumoral , Proteína del Grupo de Complementación N de la Anemia de Fanconi , Femenino , Predisposición Genética a la Enfermedad , Humanos , Mutación Missense , Proteínas Nucleares/genética , Unión Proteica , Riesgo , Transfección , Proteínas Supresoras de Tumor/genéticaRESUMEN
As the number of coils increases in multi-channel MRI receiver-coil arrays, RF cables and connectors become increasingly bulky and heavy, degrading patient comfort and slowing workflow. Inductive coupling of signals provides an attractive "wireless" approach, with the potential to reduce coil weight and cost while simplifying patient setup. In this work, multi-channel inductively coupled anterior arrays were developed and characterized for 1.5T imaging. These comprised MR receiver coils inductively (or "wirelessly") linked to secondary or "sniffer" coils whose outputs were transmitted via preamps to the MR system cabinet. The induced currents in the imaging coils were blocked by passive diode circuits during RF transmit. The imaging arrays were totally passive, obviating the need to deliver power to the coils, and providing lightweight, untethered signal reception with easily positioned coils. Single-shot fast spin echo images were acquired from 5 volunteers using a 7-element inductively coupled coil array and a conventionally cabled 7-element coil array of identical geometry, with the inductively-coupled array showing a relative signal-to-noise ratio of 0.86 +/- 0.07. The concept was extended to a larger 9-element coil array to demonstrate the effect of coil element size on signal transfer and RF-transmit blocking.
Asunto(s)
Imagen por Resonancia Magnética/instrumentación , Imagen por Resonancia Magnética/métodos , Adulto , Simulación por Computador , Diseño de Equipo , Voluntarios Sanos , Humanos , Procesamiento de Imagen Asistido por Computador , Persona de Mediana Edad , Fantasmas de Imagen , Ondas de Radio , Procesamiento de Señales Asistido por Computador , Relación Señal-Ruido , Tecnología InalámbricaRESUMEN
BACKGROUND: MRI can identify patients with obstructive coronary artery disease by imaging the left ventricular myocardium during a first-pass contrast bolus in the presence and absence of pharmacologically induced myocardial hyperemia. The purpose of this multicenter dose-ranging study was to determine the minimally efficacious dose of gadopentetate dimeglumine injection (Magnevist Injection; Berlex Laboratories) for detecting obstructive coronary artery disease. METHOD AND RESULTS: A total of 99 patients scheduled for coronary artery catheterization as part of their clinical evaluation were enrolled in this study. Patients were randomized to 1 of 3 doses of gadopentate dimeglumine: 0.05, 0.10, or 0.15 mmol/kg. First-pass perfusion imaging was performed during hyperemia (induced by a 4-minute infusion of adenosine at a rate of 140 microg x kg(-1) x min(-1)) and then again in the absence of adenosine with otherwise identical imaging parameters and the same contrast dose. Perfusion defects were evaluated subjectively by 4 blinded reviewers. Receiver-operating curve analysis showed that the areas under the receiver-operating curve were 0.90, 0.72, and 0.83 for the low-, medium-, and high-contrast doses, respectively, compared with quantitative coronary angiography (diameter stenosis > or =70%). For the low-dose group, mean sensitivity was 93+/-0%, mean specificity was 75+/-7%, and mean accuracy was 85+/-3%. CONCLUSIONS: First-pass perfusion MRI is a safe and accurate test for identifying patients with obstructive coronary artery disease. A low dose of 0.05 mmol/kg gadopentetate dimeglumine is at least as efficacious as higher doses.
Asunto(s)
Circulación Coronaria , Enfermedad Coronaria/patología , Imagen por Resonancia Magnética/métodos , Miocardio/patología , Adenosina , Anciano , Área Bajo la Curva , Cateterismo Cardíaco , Medios de Contraste/administración & dosificación , Angiografía Coronaria , Enfermedad Coronaria/diagnóstico por imagen , Relación Dosis-Respuesta a Droga , Reacciones Falso Positivas , Femenino , Gadolinio DTPA/administración & dosificación , Humanos , Hiperemia/inducido químicamente , Masculino , Persona de Mediana Edad , Estudios Prospectivos , Curva ROC , Sensibilidad y Especificidad , Método Simple CiegoRESUMEN
Contrast-enhanced magnetic resonance angiography (CE MR angiography) has benefited from advancements in MR imaging speed, pulse sequence design, and dedicated equipment and algorithms for its performance. These improvements have greatly expanded the number of options available to the operator and enabled the application of CE MR angiography to a broader range of clinical applications. In this article, the various timing options, pulse sequence innovations, and contrast administration concerns related to clinical CE MR angiography are reviewed. Pertinent issues related to multiphase and multistation bolus chase CE MR angiography also will be discussed.
Asunto(s)
Medios de Contraste , Gadolinio , Aumento de la Imagen/métodos , Angiografía por Resonancia Magnética/métodos , HumanosRESUMEN
A comparison between the prospective and retrospective respiratory navigator gating in MR coronary angiography was performed with eight normal subjects. A three-dimensional (3D) ECG-gated fast gradient echo pulse sequence was used for image data acquisition. The results show that the MR coronary angiography obtained using retrospective gating retains a considerable amount of motion artifacts. In this study, the images acquired using prospective navigator gating demonstrated significantly reduced motion artifacts (p = 0.009), improved vessel visibility (p = 0.021) with reduced imaging time (p = 0.013) compared to the images obtained using retrospective navigator gating.
Asunto(s)
Angiografía Coronaria , Angiografía por Resonancia Magnética/métodos , Movimiento (Física) , Músculos Respiratorios/diagnóstico por imagen , Músculos Respiratorios/fisiología , Adulto , Arterias/ultraestructura , Artefactos , Vasos Coronarios/ultraestructura , Humanos , Masculino , Estudios Prospectivos , Intensificación de Imagen Radiográfica , Valores de Referencia , Estudios RetrospectivosRESUMEN
A new method was investigated for improving the efficiency of ECG-gated coronary magnetic resonance angiography (CMRA) by accurate, automated tracking of the vessel motion over the cardiac cycle. Vessel tracking was implemented on a spiral gradient-echo pulse sequence with sub-millimeter in-plane spatial resolution as well as high image signal to noise ratio. Breath hold 2D CMRA was performed in 18 healthy adult subjects (mean age 46 +/- 14 years). Imaging efficiency, defined as the percentage of the slices where more than 30 mm of the vessel is visualized, was computed in multi-slice spiral scans with and without vessel tracking. There was a significant improvement in the efficiency of the vessel tracking sequence compared to the multi-slice sequence (56% vs. 32%, P < 0.001). The imaging efficiency increased further when the true motion of the coronary arteries (determined using a cross correlation algorithm) was used for vessel tracking as opposed to a linear model for motion (71% vs. 57%, P < 0.05). The motion of the coronary arteries was generally found to be linear during the systolic phase and nonlinear during the diastolic phase. The use of subject-tailored, automated tracking of vessel positions resulted in improved efficiency of coronary artery illustration on breath held 2D CMRA.
Asunto(s)
Angiografía Coronaria/métodos , Angiografía por Resonancia Magnética/métodos , Vasos Coronarios/fisiología , Femenino , Humanos , Masculino , Persona de Mediana EdadRESUMEN
The purposes of our study were to investigate the benefits of using a single dose of an extracellular contrast agent for coronary magnetic resonance angiography (CMRA) and to determine the relative benefits of arterial-phase vs. delayed-phase image acquisition. The right coronary artery was imaged in 10 healthy adults using a breath-hold, two-dimensional fast gradient echo pulse sequence designed for vessel tracking (multiphase, multislice image acquisition). Pre- and postcontrast CMRA was performed. Postcontrast imaging consisted of arterial- and delayed-phase CMRA following a 15 mL bolus (single dose) of contrast media and of delayed-phase imaging following a cumulative 45 mL contrast dose (triple dose). Contrast-enhanced CMRA provided a significantly higher (P < 0.001) signal-to-noise ratio (SNR) and contrast-to-noise ratio (CNR) than noncontrast CMRA. CNR was highest for single-dose arterial-phase CMRA (13.1 +/- 4.5) and triple-dose delayed-phase CMRA (13.0 +/- 4.8), followed by single-dose delayed-phase CMRA (8.4 +/- 3.5) and noncontrast CMRA (4.2 +/- 1.8). Single-dose arterial-phase CMRA provided the best visualization of the distal right coronary artery and was preferred for blinded physician assessments. We concluded that utilization of a single dose of extracellular contrast media improves CMRA, especially if timed for arterial-phase imaging. J. Magn. Reson. Imaging 2001;13:682-689.
Asunto(s)
Medios de Contraste/administración & dosificación , Angiografía Coronaria , Vasos Coronarios/patología , Gadolinio DTPA , Aumento de la Imagen , Procesamiento de Imagen Asistido por Computador , Angiografía por Resonancia Magnética , Adulto , Relación Dosis-Respuesta a Droga , Femenino , Humanos , Infusiones Intravenosas , Masculino , Persona de Mediana Edad , Valores de ReferenciaRESUMEN
PURPOSE: To investigate the feasibility of preferential arterial imaging using gadolinium-enhanced thick-slice phase-contrast imaging. METHODS: Six healthy volunteers were studied using a peripheral-gated segmented k-space CINE phase-contrast pulse sequence using four views per RR interval with flow encoding in the superior-inferior direction. Images at the level of the popiteal trifurcation were acquired postcontrast with different section thicknesses (4-8 cm) and VENC values (20-150 cm/sec), and phase-difference processing. RESULTS: The post-gadolinium contrast-enhanced thick-slice phase-contrast acquisitions demonstrated the ability to visualize the tibio-peroneal (trifurcation) arteries, especially in systole. With MR contrast agents, the signal from blood is raised significantly above that of stationary tissue from T(1) shortening such that the partial volume artifact is reduced in thick-slice acquisitions. Furthermore, by selecting the VENC value as a function of the cardiac cycle, the noise floor can be raised to selectively suppress flow values less than that of the noise threshold, allowing better accentuation of arterial structures at systole. CONCLUSIONS: Thick-slice phase-contrast acquisition with phase-difference processing has been observed to reduce partial volume artifacts when an MR contrast agent substantially increases signal in the vasculature over that of normal background tissue. Preferential arterial images can be obtained by either increasing the VENC value to selectively suppress signal from slow flow in the veins or by subtracting the diastolic phase image from the peak systolic phase image. J. Magn. Reson. Imaging 2001;13:714-721.
Asunto(s)
Aumento de la Imagen , Procesamiento de Imagen Asistido por Computador , Pierna/irrigación sanguínea , Angiografía por Resonancia Magnética , Imagen por Resonancia Cinemagnética , Arterias Tibiales/anatomía & histología , Adulto , Artefactos , Velocidad del Flujo Sanguíneo/fisiología , Medios de Contraste , Femenino , Gadolinio , Compuestos Heterocíclicos , Humanos , Masculino , Persona de Mediana Edad , Compuestos Organometálicos , Valores de Referencia , Sensibilidad y Especificidad , Sístole/fisiologíaRESUMEN
A method of three-station three-dimensional magnetic resonance (MR) angiography of the lower extremities with segmented volume acquisition is presented. Three-dimensional MR angiographic data were acquired in two passes, with the central k-space views acquired during the arterial phase for the more proximal stations. This allowed a faster bolus injection rate and potentially improved visualization of the tibioperoneal arteries.
Asunto(s)
Pierna/irrigación sanguínea , Angiografía por Resonancia Magnética/métodos , Adulto , Estudios de Casos y Controles , Medios de Contraste , Estudios de Factibilidad , Femenino , Humanos , Imagenología Tridimensional , Masculino , Persona de Mediana Edad , Arterias Tibiales/anatomía & histología , Factores de TiempoRESUMEN
The authors evaluated a magnetization preparation scheme with a "notched" section profile for T1-weighted first-pass myocardial perfusion magnetic resonance (MR) imaging at 1.5 T. The pulse sequence consisted of a preparation sequence followed by an interleaved gradient-echo echo-planar sequence. Image contrast was evaluated in a feasibility study in 12 adult patients. The notched saturation pulse allowed long magnetization recovery times without sacrificing section coverage. Image contrast between normal and ischemic myocardium was excellent.
Asunto(s)
Enfermedad Coronaria/diagnóstico , Imagen Eco-Planar/métodos , Electrocardiografía , Aumento de la Imagen , Adenosina , Anciano , Medios de Contraste , Prueba de Esfuerzo , Estudios de Factibilidad , Femenino , Gadolinio DTPA , Humanos , Masculino , Persona de Mediana Edad , Isquemia Miocárdica/diagnósticoRESUMEN
In this pilot study, using a standard 40 mL gadolinium (Gd) chelate contrast dose, dual-rate (first 20 mL at 0.5 mL/sec; remaining 20 mL at 1.5 mL/sec) and fixed-rate (entire 40 mL dose at either 0.7 mL/sec or 2.0 mL/sec) injection schemes for multistation, bolus-chase magnetic resonance angiography (MRA) were compared in normal volunteers. Signal-to-noise ratio, contrast-to-noise ratio, and physician preference were determined for nine arterial segments. At the terminal station (calf), the dual-rate contrast injection improved arterial signal and contrast compared with both fixed-rate injection schemes and improved subjective vessel appearance compared with the 2.0 mL/sec, but not the 0.7 mL/sec, fixed-rate scheme.
Asunto(s)
Medios de Contraste , Gadolinio , Angiografía por Resonancia Magnética/métodos , Adulto , Análisis de Varianza , Arterias/anatomía & histología , Relación Dosis-Respuesta a Droga , Femenino , Humanos , Inyecciones Intravenosas , Masculino , Persona de Mediana Edad , Proyectos Piloto , Intensificación de Imagen Radiográfica , Valores de Referencia , Sensibilidad y Especificidad , Factores de TiempoRESUMEN
A connectivity algorithm combined with a new gray-level morphological filter dramatically improves the segmentation of tortuous coronary arteries from 3D MRI. Small coronary arteries are segmented from the larger ventricles with a new filter. These blood vessels are segmented from the noise background with connectivity. Coronary angiograms were computed in nine datasets acquired on volunteers with 3D stack of spirals and contrast-enhanced navigator sequences by both a maximum intensity projection and surface rendering. Surface images provided depth information needed to distinguish branching arteries from crossing veins. Magn Reson Med 43:892-895, 2000.
Asunto(s)
Vasos Coronarios/anatomía & histología , Aumento de la Imagen/métodos , Angiografía por Resonancia Magnética/instrumentación , Algoritmos , Circulación Coronaria/fisiología , Humanos , Angiografía por Resonancia Magnética/métodos , Valores de Referencia , Sensibilidad y EspecificidadRESUMEN
To follow the motion of the coronary artery in magnetic resonance angiography, the authors evaluated vessel tracking, a method for prospective adjustment of the section location as a function of the delay from the cardiac trigger. In 10 volunteers and four patients, this method allowed the vessel to be maintained in the plane of acquisition throughout the cardiac cycle. With a single-phase multisection sequence, vessel-tracking acquisitions had an efficiency of 0.68 +/- 0.04 for both the right and left coronary arteries compared with 0.19 +/- 0.03 for a non-vessel-tracking acquisition (P < .001).
Asunto(s)
Angiografía Coronaria , Vasos Coronarios/patología , Angiografía por Resonancia Magnética , Contracción Miocárdica/fisiología , Adulto , Anciano , Artefactos , Electrocardiografía , Femenino , Humanos , Masculino , Persona de Mediana Edad , Valores de ReferenciaRESUMEN
Coronary artery magnetic resonance imaging strategies have tended to focus on the use of a single method performed during either breath-holding or free-breathing for all patients. However, significant variations exist among patients in terms of breath-holding ability and respiratory regularity that make the use of a single technique alone not universally successful. Therefore, it is prudent to make available a number of magnetic resonance imaging methods such that an appropriate respiratory motion reduction strategy can be tailored to suit the patient's respiratory pattern and characteristics. A tailored approach that can draw on different image acquisition techniques for coronary artery imaging is presented. A decision tree is proposed to triage patients into imaging regimes with the greatest probability of success, according to the patient's ability to breath-hold or exhibit steady respiration. Methods include volume free-breathing acquisitions using navigator echoes for respiratory monitoring in the 8- to 10-min scan time range, two-dimensional spiral navigators (2- to 3-min scan time), breath-held multislice and vessel-tracking spirals (16- to 20-second scan time), and real-time imaging approaches incorporating adaptive signal averaging. The development of multiple acquisition strategies substantially improves the opportunities to generate high-quality, diagnostic images of the coronary arteries.
Asunto(s)
Enfermedad Coronaria/diagnóstico , Vasos Coronarios/anatomía & histología , Angiografía por Resonancia Magnética/métodos , Atención Dirigida al Paciente , Respiración , Femenino , Humanos , Masculino , Sensibilidad y EspecificidadRESUMEN
Bolus chase 3-dimensional MR angiography (3D MRA) is a recent development that extends the effective field of view for arterial imaging from the typical single 40-50 cm to over 100 cm. This technique is well suited for imaging long vascular territories such as the lower extremity. Bolus chase peripheral 3D MRA is achieved with overlapping 3D gradient-echo scans during the arterial transit of a single intravenous injection of gadolinium-chelate contrast media. This technique can depict the arteries from the infrarenal aorta to the ankles in less than 2 minutes. The initial experiences with bolus chase peripheral MRA using an automated algorithm that controls both table translation and 3D data acquisition are described. Suggestions for future refinements to the technique are also discussed.
Asunto(s)
Medios de Contraste/administración & dosificación , Gadolinio/administración & dosificación , Aumento de la Imagen/métodos , Angiografía por Resonancia Magnética/métodos , Enfermedades Vasculares Periféricas/diagnóstico , Algoritmos , Análisis de Fourier , Humanos , Inyecciones IntravenosasRESUMEN
A fast and computationally efficient method for detecting and tracking the displacement of a reference structure within the body using MR imaging is described. This method is used to determine the position of the diaphragm in order to synchronize the data acquisition to the same relative position of the abdominal and thoracic organs, thereby minimizing or eliminating respiratory motion artifacts. The method described uses the time domain linear phase shift of a reference structure to determine its spatial positional displacement as a function of the respiratory cycle. The signal from a two-dimensional rectangular excitation column is first Fourier-transformed to the image domain, apodized, and then transformed back to the time domain. The relative displacement of a target edge in the image domain is determined from an autocorrelation of the resulting time domain information. This technique was found to require between three and eight times less computation than either cross-correlation or least-squares analysis, depending on the navigator parameters. Magn Reson Med 42:548-553, 1999.
Asunto(s)
Vasos Coronarios/anatomía & histología , Diafragma/anatomía & histología , Imagen por Resonancia Magnética/métodos , Algoritmos , Artefactos , Análisis de Fourier , Humanos , Análisis de los Mínimos Cuadrados , Movimiento , Fantasmas de Imagen , Procesamiento de Señales Asistido por ComputadorRESUMEN
Arterial contrast enhancement on MR angiography images is dependent on the adequate timing of the contrast bolus arrival to the acquisition of the center of k-space. Different strategies for achieving this goal are described. The more advanced techniques are aimed at making the detection of the peak arrival and the start of data acquisition more robust in order to generate images with maximal arterial-background contrast with minimal venous signal contamination.
Asunto(s)
Medios de Contraste , Aumento de la Imagen/métodos , Angiografía por Resonancia Magnética/métodos , Arterias/anatomía & histología , Artefactos , Sangre , Medios de Contraste/administración & dosificación , Análisis de Fourier , Humanos , Procesamiento de Imagen Asistido por Computador/métodos , Factores de Tiempo , Venas/anatomía & histologíaRESUMEN
Gadolinium (Gd)-enhanced three-dimensional (3D) magnetic resonance angiography (MRA) is a quick method for performing noninvasive diagnostic angiography. A major technical obstacle to the successful implementation of this technique, however, is the proper coordination of the data acquisition with the contrast bolus. In this article, the use of an automated bolus-detection algorithm (MR SmartPrep), which triggers the initiation of data acquisition for Gd-enhanced 3D MRA is reviewed. Potential applications of this evolving technique are illustrated.
Asunto(s)
Medios de Contraste/administración & dosificación , Gadolinio , Aumento de la Imagen , Angiografía por Resonancia Magnética , Algoritmos , Arteriopatías Oclusivas/diagnóstico , Gadolinio/administración & dosificación , Humanos , Aumento de la Imagen/métodos , Infusiones Intravenosas , Angiografía por Resonancia Magnética/métodos , Reproducibilidad de los ResultadosRESUMEN
Our goal was to evaluate whether contrast-enhanced three-dimensional MR angiography using the MR Smartprep technique would enable us to obtain arterial-phase MR angiograms of the carotid and vertebral arteries. The study included 35 patients with suspected lesions of the neck in whom the MR Smartprep technique was used for MR angiography performed with a 1.5-T superconducting system. The tracker volume was placed primarily in the middle part of the right common carotid artery. The imaging volume was placed in a coronal direction to include the carotid and vertebral arteries from the aortic arch to the skull base. A centric phase-ordering scheme was used. Imaging times were 20 to 38 seconds for 14 patients and 11 to 16 seconds for 21 patients. By using a smaller tracker volume and an imaging time of less than 16 seconds, we were able to achieve a 100% successful triggering rate and to delineate selectively arterial-phase carotid and vertebral arteries with almost no venous contamination. Contract-enhanced 3-D MR angiography with the MR Smartprep technique was useful for showing arterial-phase carotid and vertebral arteries selectively.