Effect of bulk tissue motion on quantitative perfusion and diffusion magnetic resonance imaging

The effect of irreproducible bulk tissue motions upon quantification of tissue perfusion and diffusion was studied via computer simulation of random phase error in conventional phase-encoded perfusion/diffusion MRI. Simulations using acquisition parameters typical for human brain studies demonstrate that bulk motion irreproducibility of approximately 60 microns/s can produce phase instability on the order of 20 degrees which overwhelms estimates of perfusion fraction and produces significant errors in diffusion values. Bulk tissue motion control of the human brain via cardiac gating and substantial head restraint was studied by direct measurement of voxel phase stability. Phase instability of 10 degrees to 20 degrees was observed from right-to-left and anterior-to-posterior motions and significantly greater phase variability from superior-to-inferior motion. The spatial pattern of phase variability indicates the source is likely a mixture of cardiac pulsation and respiration.     

多模态MRI在定量评价脂肪组织和脂肪肝中的研究进展

脂肪代谢异常与机体代谢性疾病和炎症反应的发生和发展密切相关,可引起全身多脏器功能障碍。传统的脂肪组织检查方法多为有创性检查,多模态MRI技术能够对脂肪组织的功能以及异位脂质沉积进行全面的评估,可为脂肪相关代谢性疾病的诊断、疾病进展监测和治疗效果的评价提供大量信息。就多模态MRI技术在定量评价脂肪组织和脂肪肝中的技术进展与研究现状进行综述。     

Optimized quantitative magnetic resonance spectroscopy for clinical routine

Several practical obstacles in data handling and evaluation complicate the use of quantitative localized magnetic resonance spectroscopy (qMRS) in clinical routine MR examinations. To overcome these obstacles, a clinically feasible MR pulse sequence protocol based on standard available MR pulse sequences for qMRS has been implemented along with newly added functionalities to the free software package jMRUI‐v5.0 to make qMRS attractive for clinical routine. This enables (a) easy and fast DICOM data transfer from the MR console and the qMRS‐computer, (b) visualization of combined MR spectroscopy and imaging, (c) creation and network transfer of spectroscopy reports in DICOM format, (d) integration of advanced water reference models for absolute quantification, and (e) setup of databases containing normal metabolite concentrations of healthy subjects. To demonstrate the work‐flow of qMRS using these implementations, databases for normal metabolite concentration in different regions of brain tissue were created using spectroscopic data acquired in 55 normal subjects (age range 6–61 years) using 1.5T and 3T MR systems, and illustrated in one clinical case of typical brain tumor (primitive neuroectodermal tumor). The MR pulse sequence protocol and newly implemented software functionalities facilitate the incorporation of qMRS and reference to normal value metabolite concentration data in daily clinical routine. Magn Reson Med, 2013. © 2012 Wiley Periodicals, Inc.     

Measuring cartilage morphology with quantitative magnetic resonance imaging

Magnetic resonance imaging (MRI) is a three-dimensional imaging technique with unparalleled ability to delineate articular cartilage morphology in health and disease. In this article we will review work on the assessment of cartilage morphology with quantitative magnetic resonance imaging and its relevance to the study of cartilage anatomy, physiology, deformation, disease status, disease progression, and response to treatment. The review outlines available pulse sequences and techniques for segmentation and morphological analysis of cartilage morphology. It addresses the accuracy (validity) and precision (reproducibility) of these techniques and summarizes studies on cartilage deformation in intact joints. This article will also review work on determinants and functional adaptation of cartilage morphology and describe changes seen in osteoarthritis. We conclude that fat-suppressed or water excitation gradient-echo magnetic resonance sequences and state-of-the-art digital image analysis techniques display high accuracy and adequate precision for quantitative assessment of cartilage morphology. This renders these techniques powerful and promising tools for cartilage and osteoarthritis research.     

The acellular matrix (ACM) for bladder tissue engineering: A quantitative magnetic resonance imaging study

Bladder acellular matrices (ACMs) derived from natural tissue are gaining increasing attention for their role in tissue engineering and regeneration. Unlike conventional scaffolds based on biodegradable polymers or gels, ACMs possess native biomechanical and many acquired biologic properties. Efforts to optimize ACM‐based scaffolds are ongoing and would be greatly assisted by a noninvasive means to characterize scaffold properties and monitor interaction with cells. MRI is well suited to this role, but research with MRI for scaffold characterization has been limited. This study presents initial results from quantitative MRI measurements for bladder ACM characterization and investigates the effects of incorporating hyaluronic acid, a natural biomaterial useful in tissue‐engineering and regeneration. Measured MR relaxation times (T₁, T₂) and diffusion coefficient were consistent with increased water uptake and glycosaminoglycan content observed on biochemistry in hyaluronic acid ACMs. Multicomponent MRI provided greater specificity, with diffusion data showing an acellular environment and T₂ components distinguishing the separate effects of increased glycosaminoglycans and hydration. These results suggest that quantitative MRI may provide useful information on matrix composition and structure, which is valuable in guiding further development using bladder ACMs for organ regeneration and in strategies involving the use of hyaluronic acid. Magn Reson Med, 2010. © 2010 Wiley‐Liss, Inc.     

Qualitative und quantitative assessment of myocardial perfusion using magnetic resonance imaging

Summary Purpose: Purpose of this study was to test a triple slice saturation recovery turbo FLASH sequence for myocardial perfusion imaging. In addition data-evaluation-tools for qualitative and quantitative perfusion parameters are presented and preliminary tested. Material and Methods: We examined 8 healthy volunteers and 4 patients with myocardial infarction. Parameters of the saturation recovery turbo FLASH sequence were as follows: TR = 2.5 msec, TE = 1.2 msec, α = 8 °, 3 slices, thickness 10 mm. For data analysis signal-intensity time curves were calculated pixel by pixel and evaluated for signal-intensity-increase over baseline and signal-intensity-upslope. Images were displayed color-coded. For quantitative data analysis we used the indicator dilution theory and developed a deconvolution algorithm which takes the arterial input function into account to calculate the myocardial mean transit time (MTT). Results: The color-coded parametermaps showed uniform conditions in normal myocardium of volunteers, but reduced signal-intensity-increase over baseline and signal-intensity-upslope for infarcted areas in patients. The MTTs calculated using our algorithm were significantly shorter than those assessed with previous methods and matched better with values derived from literature. Infarcted areas show prolonged MTTs in comparison to normal myocardium. Conclusion: A triple slice saturation recovery turbo FLASH sequence is suitable for myocardial perfusion imaging. Color-coded parametermaps can visualize hypoperfused areas. For calculating myocardial MTTs using indicator dilution therapy a deconvolution algorithm is necessary. Eingegangen am 23. M?rz 1997 Angenommen am 26. M?rz 1997     

Soft tissue enhancement on time-resolved peripheral magnetic resonance angiography

PURPOSE: To evaluate the incidence and locations of soft tissue enhancement on time-resolved two-dimensional projection magnetic resonance angiography (MRA) of the calf and foot. MATERIALS AND METHODS: Time-resolved two-dimensional projection MRA of the knee, calf, and foot, performed at 1.5 Tesla using the head coil, was retrospectively reviewed in 326 patients. Soft tissue enhancement of the foot was identified and graded by blinded review. Subsequently, patient medical records were reviewed to determine the presence or absence of diabetes, cellulitis, gangrene, and ulceration of the foot and presence of neuropathic joints. RESULTS: Enhancing spots were identified in 228 patients. For those feet without clinical abnormalities, diabetic patients had an average of 1.2 enhancing spots per foot, while nondiabetics had only 0.6 (P < 0.001). Higher-grade lesions were more prevalent in diabetics and in heavier patients. Of 64 patients with follow-up, 8 (13%) developed cellulitis (N = 4) or ulceration (N = 4) at the location of an enhancing spot, including 5 diabetic and 3 nondiabetic patients. CONCLUSION: Pedal soft tissue enhancement frequently occurs on time-resolved gadolinium (Gd):MRA of the feet. The etiology is uncertain, but the high frequency in diabetic patients and observation of progression to cellulitis/ulceration suggest this soft tissue enhancement may identify sites of subclinical pedal soft tissue injury.     

Abdominal neuroblastoma: magnetic resonance imaging and tissue characterization

Magnetic resonance imaging was performed in eight children with abdominal neuroblastomas. Five patients had serial examinations after diagnosis, and 15 computed tomography (CT) scans were available for comparison. MR imaging was as precise as CT in detecting the presence or absence of liver involvement and more efficient in determining the relationship of tumor to vascular structures. However, it did not differentiate tumor from normal kidney as accurately as CT. Inversion recovery (IR) images yielded the greatest soft-tissue contrast resolution between liver and tumor. T1 values of tumor were much higher than those of normal liver but overlapped those of normal kidneys. T2 values of tumor were significantly higher than those of the liver and were slightly, but not significantly, lower than those of the kidneys. Either T1- or T2- weighted pulse sequences should, therefore, provide adequate liver-tumor differentiation, but more heavily T2- weighted images appear necessary to distinguish between tumor and kidney. T1 values of tumors usually decreased with rapid tumor regression, while T2 values changed independently. The ability to quantitate tissue parameters helps in selecting appropriate imaging sequences and may be of use in following the progress of tumors.     

Improved cerebellar tissue classification on magnetic resonance images of brain

Purpose

To develop and implement a method for improved cerebellar tissue classification on the MRI of brain by automatically isolating the cerebellum prior to segmentation.

Materials and Methods

Dual fast spin echo (FSE) and fluid attenuation inversion recovery (FLAIR) images were acquired on 18 normal volunteers on a 3 T Philips scanner. The cerebellum was isolated from the rest of the brain using a symmetric inverse consistent nonlinear registration of individual brain with the parcellated template. The cerebellum was then separated by masking the anatomical image with individual FLAIR images. Tissues in both the cerebellum and rest of the brain were separately classified using hidden Markov random field (HMRF), a parametric method, and then combined to obtain tissue classification of the whole brain. The proposed method for tissue classification on real MR brain images was evaluated subjectively by two experts. The segmentation results on Brainweb images with varying noise and intensity nonuniformity levels were quantitatively compared with the ground truth by computing the Dice similarity indices.

Results

The proposed method significantly improved the cerebellar tissue classification on all normal volunteers included in this study without compromising the classification in remaining part of the brain. The average similarity indices for gray matter (GM) and white matter (WM) in the cerebellum are 89.81 (±2.34) and 93.04 (±2.41), demonstrating excellent performance of the proposed methodology.

Conclusion

The proposed method significantly improved tissue classification in the cerebellum. The GM was overestimated when segmentation was performed on the whole brain as a single object. J. Magn. Reson. Imaging 2009;29:1035–1042. © 2009 Wiley‐Liss, Inc.     

Real-time magnetic resonance imaging of laser heat deposition in tissue

We applied diffusion-sensitive echo planar (Instascan) imaging to study thermal changes caused by a Nd:YAG laser. Images of phantom materials and normal rabbit brain tissue in vivo, acquired in 150 ms, every 2s, clearly showed the dynamics of temperature-related signal intensity changes in the regions irradiated by the laser.     

Gadolinium-DTPA enhancement of soft tissue tumors in magnetic resonance imaging

In a clinical study of 13 patients, gadolinium-DTPA (Gd-DTPA) was used for enhancement of soft tissue tumors at magnetic resonance imaging. Gd-enhanced T1 sequences were found to give additional information concerning tumor vascularity in 11 cases, tumor necrosis in 2 cases and tumor delineation in one case, compared with conventional T1 and T2 weighted spin echo sequences. If Gd-enhanced sequences were to be used as the only source of information, accurate assessment of tissue composition of the tumor would not have been possible. Furthermore, valuable information regarding tumor delineation towards surrounding fat may be lost.     

定量磁共振对膝关节软骨的应用研究进展

膝关节软骨在维持关节正常运动中起着缓冲、减震及润滑的关键作用。软骨定量磁共振成像是一种比较新的磁共振成像技术,能够对软骨内的细微组织成分进行量化评估,是评价膝关节软骨及其病变的一种有效的影像学检查方法。本文对膝关节软骨的正常组织结构和定量磁共振在膝关节软骨的量化评估及临床应用予以综述。     

Synthetic magnetic resonance imaging for quantitative parameter evaluation of temporomandibular joint disorders

Objective:This study investigated the usefulness of quantitative parameters [longitudinal relaxation (T1), transverse relaxation (T2), and proton density (PD)] obtained with synthetic magnetic resonance imaging (MRI) in assessing the progression of temporomandibular joint (TMJ) disorders.Methods:For individual TMJ disorder diagnoses, the presence of disc displacement in MRI and the osseous change in cone-beam CT were investigated. Joints were classified into three stages: (1) silent stage, no disc displacement or osseous change; (2) incipient stage, presence of disc displacement and absence of osseous change; and (3) progressed stage, both disc displacement and osseous change. In synthetic MRI, the T1, T2, and PD values of the condyle bone marrow were measured simultaneously. The median T1, T2, and PD values were analyzed according to disc displacement, osseous changes, and joint stage.Results:Significant differences were observed in the T1 and PD values of joints with disc displacement or condylar osseous change compared to normal joints. The T1 and PD values also differed between the silent and progressed stages. The PD value differed between the silent and incipient groups, while the T2 value did not differ significantly among the three groups.Conclusion:The PD and T1 values of condylar bone marrow obtained from synthetic MRI can be used as sensitive indicators of TMJ disorder progression. The PD value of the bone marrow showed potential as a useful biomarker for recognizing the initial stages of TMJ disorders. Synthetic MRI is useful for the simultaneous acquisition of effective MRI parameters for evaluating TMJ disorders.     

Quantitative tissue characterisation in pancreatic disease using magnetic resonance imaging

Twenty-nine patients, 27 of whom had either inflammatory disease of the pancreas or pancreatic tumour, were studied by magnetic resonance imaging (MRI) and computed tomography (CT). Six healthy volunteers were studied by MRI alone. The pancreatic T1 and T2 relaxation times were calculated using a multipoint iterative method with data from seven total saturation recovery and six spin echo sequences. Magnetic resonance imaging can demonstrate the normal pancreas and a variety of pathological processes greater than 1-2 cm in size, but with less spatial resolution than CT. The relaxation-time results indicated no significant discrimination between chronic pancreatitis and pancreatic tumour. A significant elevation in the relaxation times was observed, however, in those patients with calcific chronic pancreatitis compared with the non-calcific chronic pancreatitic group and normal controls, suggesting a different pathophysiology for the two subgroups of chronic pancreatitis. The active phase of acute pancreatitis was associated with significantly elevated relaxation times, which returned to normal levels during the resolved phase of the disease. Associated extrapancreatic fluid collections were characterised by their very long relaxation times. The problems associated with spatial resolution, respiratory motion and lack of quantitative tissue characterisation suggest that MRI of the pancreas, using present methods, is unlikely to contribute to the overall management of patients with exocrine pancreatic disease.     

Role of magnetic resonance imaging in the tissue characterization of tumors

Aim of this article is to examine the possibilities and the limits of MR imaging in oncology, with special regard to the tissue characterization of tumors. Basic information is given on the fundamental parameters of MR, and the concept of image contrast is discussed, with a comparison between the image in conventional radiology and in MR. Factors affecting MR parameters and influencing the image contrast are analyzed; they are classified as extrinsic, or connected to the patient's conditions and to technical modalities, and as intrinsic or inherent to biological factors. Intrinsic factors are scheduled in three groups: a) tissue physico-chemical structure; b) functions or physiological conditions; c) pathological aspects. One of the most important factors related with the first group is water content. The possible influences of water content on the measurement of the proton MR relaxation times are numerous and complex. As a first approximation, relaxation times are directly related to water content; nevertheless many experimental results show that this statement is not sufficient to explain the observed variations of relaxation times in different tissues and organs. Some other data are accounted for the presence of different relaxation times of water in the same sample, and for the microtrabecular structure of the cell. In normal tissues and structures, further elements are explained on the basis of simple physico-chemical characteristics. In tumors the increase of T1 and T2 observed in experimental evaluations performed on samples of tissues, was largely confirmed in the images. To an equal extent failure of specificity of the increase of relaxation times of tumors is well documented in experimental research and in clinical experiences. In experimental research a strict comparison was made between the tumor and the tissue of origin. Increase of relaxation parameters appears related to the presence of larger fluid-filled areas, to the diminution of average cell size, and to reduced amount of rough and smooth endoplasmic reticulum. In clinical experiences good results are obtained in the ascertainment of the tumors localization and extension; macroscopic aspects connected to the peritumoral structures, inhomogeneities, and necrosis are well evaluated. New data are acquired in the study of early and late effects of radiation in patients submitted to radiotherapy for various types of tumors.     

Resection of soft tissue sarcomas with intra-operative magnetic resonance guidance.

PURPOSE: To report on a preliminary series of magnetic resonance (MR)-guided sarcoma resections. MATERIALS AND METHODS: Three patients with the skin sarcoma dermatofibrosarcoma protuberans underwent MR-guided resection. RESULTS: The extent of the tumor at MR imaging was greater in each case than suggested by clinical examination. Adequate resection margins were planned using short Tau inversion recovery (STIR) sequences and intra-operative imaging was used to confirm complete tumor excision. Histological examination confirmed clear surgical margins of at least 1 cm in each case. CONCLUSION: We believe this technique may reduce the incidence of specimen margins positive for tumor following resection, and consequently reduce the need for further excisional surgery.     

Nuclear magnetic resonance parameters for monitoring coagulation of liver tissue.

A new NMR parameter is suggested as a sensitive tool for monitoring thermal coagulation of liver tissue. That parameter is the proton magnetization exchange time (tau(MEX)) between water and the proteins. tau(MEX) was very sensitive to coagulation and insensitive to temperature, therefore representing only damage to the tissue, independent of effects caused by temperature fluctuations. The measurement of tau(MEX) by two different methods revealed the existence of two or more groups of proteins, characterized by their different transverse relaxation time, and tau(MEX).     

Computed tomography and magnetic resonance imaging findings of soft tissue perineurioma

Soft tissue perineurioma is an uncommon benign peripheral nerve sheath tumor, although it is the most common subtype of perineuriomas. We present a case of soft tissue perineurioma in the left groin of a 48-year-old man. Precontrast computed tomography showed a homogeneous hypodense mass that showed faint enhancement. The mass appeared with hypointensity on T1-weighted magnetic resonance (MR) images and heterogeneous hyperintensity on T2-weighted MR images. Slight contrast uptake was noted on enhanced T1-weighted MR images with fat suppression. Although these CT and MR imaging findings were nonspecific, the overall imaging features are similar to those of schwannomas.