Gradient moment nulling techniques require the introduction of an additional gradient on each axis for each order of motion correction to be applied. The additional gradients introduce new constraints on the sequence design and increase the demands on the gradient system. The purpose of this paper is to demonstrate techniques for optimization of gradient echo gradient moment nulling sequences within the constraints of the gradient hardware. Flow compensated pulse sequences were designed and implemented on a clinical magnetic resonance imaging system. The design of the gradient moment nulling sequences requires the solution of a linear system of equations. A Mathematica package was developed that interactively solves the gradient moment nulling problem. The package allows the physicist to specify the desired order of motion compensation and the duration of the gradients in the sequence with different gradient envelopes. The gradient echo sequences with first, second, and third order motion compensation were implemented with minimum echo time. The sequences were optimized to take full advantage of the capabilities of the gradient hardware. The sequences were used to generate images of phantoms and human brains. The optimized sequences were found to have better motion compensation than comparable standard sequences.
Axis, Cervical Vertebra ; Brain* ; Compensation and Redress* ; Humans ; Magnetic Resonance Imaging

In this work practical considerations of a pulsed arterial spin labeling MRI are presented to reliable multi-slice perfusion measurements in the human brain. Three parameters were considered in this study. First, in order to improve slice profile and inversion efficiency of a labeling pulse a high power inversion pulse of adiabatic hyperbolic secant was designed. A 900o rotation of the flip angle was provided to make a good slice profile and excellent inversion efficiency. Second, to minimize contributions of a residual magnetization between interleaved scans of control and labeling we tested three different conditions which were applied 1) only saturation pulses, 2) only spoiler gradients, and 3) combinations of saturation pulses and spoiler gradients. Applications of both saturation pulses and spoiler gradients minimized the residual magnetization. Finally, to find a minimum gap between a tagged plane and an imaging plane we tested signal changes of the subtracted image between control and labeled images with varying the gap. The optimum gap was about 20 mm. In conclusion, in order to obtain high quality of perfusion images in human brain it is important to use optimum parameters. Before routinely using in clinical studies, we recommend to make optimizations of sequence parameters.
Brain* ; Humans* ; Magnetic Resonance Imaging* ; Perfusion*

PURPOSE: A pulsed arterial spin labeling (PASL) signal usually depends on several parameters. The objective of this study was to determine the optimal parameters using simulation for perfusion signals of PASL magnetic resonance imaging (MRI). MATERIALS AND METHODS: Perfusion signals, DeltaM/M(0b), derived from the Bloch equation were evaluated in regard to the four most important parameters in PASL MRI: the tissue-to-blood coefficient (lambda), the longitudinal relaxation time of blood (T(1b)), the arterial transit delay from the application of tag (deltat), and the magnetic field strength (B0). The simulation was conducted with Mathematica software. RESULTS: First, perfusion signals differed depending on the value of lambda in brain tissue. The maximum signal, DeltaM/M(0b) = 0.390, was obtained at an inversion time (TI) = 1.53 sec for gray matter on 3T MRI. Second, perfusion signals were reduced with increasing deltat. The maximum signal, DeltaM/M0b = 0.526, was obtained at TI = 2.1 sec for deltat = 0.5 sec. Finally, perfusion signals increased with increasing B0. The maximum signal, DeltaM = 1.15, was obtained at TI = 1.52 sec for 3T MRI. CONCLUSION: We reported that the optimized TI values were obtained to provide the highest PASL signals. It is very important that optimized TI values be used to obtain high-quality perfusion signals using PASL MRI.
Brain ; Magnetic Fields ; Magnetic Resonance Imaging ; Perfusion ; Relaxation

Perfusion is a fundamental biological function that refers to the delivery of oxygen and nutrients to tissue by means of blood flow. Perfusion MRI is sensitive to microvasculature and has been applied in a wide variety of clinical applications, including the classification of tumors, identification of stroke regions, and characterization of other diseases. Perfusion MRI techniques are classified with or without using an exogenous contrast agent. Bolus methods, with injections of a contrast agent, provide better sensitivity with higher spatial resolution, and are therefore more widely used in clinical applications. However, arterial spin-labeling methods provide a unique opportunity to measure cerebral blood flow without requiring an exogenous contrast agent and have better accuracy for quantification. Importantly, MRI-based perfusion measurements are minimally invasive overall, and do not use any radiation and radioisotopes. In this review, we describe the principles and techniques of perfusion MRI. This review summarizes comprehensive updated knowledge on the physical principles and techniques of perfusion MRI.
Arteries/chemistry ; Brain Neoplasms/radiography ; Contrast Media/diagnostic use ; Humans ; Magnetic Resonance Imaging/standards/*trends ; Spin Labels ; Stroke/radiography

An echo planar imaging (EPI)-based spin-echo sequence is often used to obtain diffusion tensor imaging (DTI) data on most of the clinical MRI systems. However, this sequence is confounded with the susceptibility artifacts, especially on the temporal lobe in the human brain. Therefore, the objective of this study was to design a pulse sequence that relatively immunizes the susceptibility artifacts, but can map diffusion tensor components in a single-shot mode. A multi-slice multi-echo pulsed-gradient spin-echo (MePGSE) sequence with eight echoes wasdeveloped with selective refocusing pulses for all slices to map the full tensor. The first seven echoes in the train were diffusion-weighted allowing for the observation of diffusion in several different directions in a single experiment and the last echo was for crusher of the residual magnetization. All components of diffusion tensor were measured by a single shot experiment. The sequence was applied in diffusive phantoms. The preliminary experimental verification of the sequence was illustrated by measuring the apparent diffusion coefficient (ADC) for tap water and by measuring diffusion tensor components for watermelon. The ADC values in the series of the water phantom were reliable. The MePGSE sequence, therefore, may be useful in human brain studies.
Artifacts ; Brain ; Citrullus ; Diffusion Tensor Imaging* ; Diffusion* ; Echo-Planar Imaging ; Humans ; Magnetic Resonance Imaging* ; Temporal Lobe ; Water

OBJECTIVE: There is a rich literature confirming the default mode network found compatible with task-induced deactivation regions in normal subjects, but few investigations of alterations of the motor deactivation in patients with intracranial lesions. Therefore, we hypothesized that an intracranial lesion results in abnormal changes in a task-induced deactivation region compared with default mode network, and these changes are associated with specific attributes of allocated regions. METHODS: Blood oxygenation level dependent (BOLD) functional magnetic resonance imaging (fMRI) during a motor task were obtained from 27 intracranial lesion patients (mean age, 57.3 years; range 15-78 years) who had various kinds of brain tumors. The BOLD fMRI data for each patient were evaluated to obtain activation or deactivation regions. The distinctive deactivation regions from intracranial lesion patients were evaluated by comparing to the literature reports. RESULTS: There were additive deactivated regions according to intracranial lesions: fusiform gyrus in cavernous hemangioma; lateral occipital gyrus in meningioma; crus cerebri in hemangiopericytoma; globus pallidus, lateral occipital gyrus, caudate nucleus, fusiform gyrus, lingual gyrus, claustrum, substantia nigra, subthalamic nucleus in GBM; fusiform gyrus in metastatic brain tumors. CONCLUSION: There is increasing interest in human brain function using fMRI. The authors report the brain function migrations and changes that occur in patients with intracranial lesions.
Basal Ganglia ; Brain ; Brain Neoplasms ; Caudate Nucleus ; Globus Pallidus ; Hemangioma, Cavernous ; Hemangiopericytoma ; Humans ; Magnetic Resonance Imaging ; Meningioma ; Oxygen ; Substantia Nigra ; Subthalamic Nucleus

Spin echo gradient moment nulling pulse sequences were designed and implemented on a clinical magnetic resonance imaging system. A new technique was introduced for flow compensation that minimized echo time and effectively suppresses unwanted echoes on the slice selection gradient axis in spin echo sequences. A unified gradient shape was used in all orders of flow compensation up to the third order. A dual-purpose gradient was applied for flow compensation and to reduce unwanted artifacts. The sequences were used to generate images of phantoms and/or human brains. This technique was especially good at reducing eddy currents and artifacts related to imperfection of the refocusing pulse. The developed sequences were found to have shorter echo times and better flow compensation in through-plane flow than those of the previous models that were used by other investigators.
Artifacts ; Axis, Cervical Vertebra* ; Brain ; Compensation and Redress* ; Humans ; Magnetic Resonance Imaging ; Research Personnel

PURPOSE: To generate a Korean specific brain template, especially in patients with Alzheimer's disease (AD) by optimizing the voxel-based analysis. MATERIALS AND METHODS: Three-dimensional T1-weighted images were obtained from 123 subjects who were 43 cognitively normal subjects and patients with 44 mild cognitive impairment (MCI) and 36 AD. The template and the corresponding aprior maps were created by using the matched pairs approach with considering differences of age, gender and differential diagnosis (DDX). We measured several characteristics in both our and the MNI templates, including in the ventricle size. Also, the fractions of gray matter and white matter voxels normalized by the total intracranial were evaluated. RESULTS: The high resolution template and the corresponding aprior maps of gray matter, white matter (WM) and CSF were created with the voxel-size of 1 x 1 x 1 mm. Mean distance measures and the ventricle sizes differed between two templates. Our brain template had less gray matter and white matter areas than the MNI template. There were volume differences more in gray matter than in white matter. CONCLUSION: Gray matter and/or white matter integrity studies in populations of Korean elderly and patients with AD are needed to investigate with this template.
Aged ; Alzheimer Disease ; Brain ; Diagnosis, Differential ; Humans ; Mild Cognitive Impairment

We report magnetic resonance image (MRI) and magnetic resonance spectroscopy (MRS) findings in a patient of cerebral fat embolism (CFE) occurred in a 26-year-old woman after an autologous fat injection into the face. After initial neurologic symptom onset, MRI and MRS data were obtained two times to investigate repeated CFE. We obtained the MRS data in the two different time intervals and two different echo times to compare the lesions with normal brain parenchyma. The results of MRS data showed that a decrease in N-acetyl-aspartate, an increase in lactate and a very high early peak of free lipids between 0.9 and 1.4 ppm were obtained at the acute infarcted lesion as compared with normal brain parenchyma. In addition, these findings were more clearly detected on short echo time spectrum rather than long spectrum. A close relationship between the clinical manifestations and MRI and MRS findings of the brain can helpful to distinguish CFE with other conditions and to evaluate the cause materials of infarctions rather than conventional MRI or diffusion-weighted imaging.
Adult ; Brain ; Embolism, Fat ; Female ; Humans ; Infarction ; Lactic Acid ; Magnetic Resonance Spectroscopy ; Magnetics ; Magnets ; Neurologic Manifestations

PURPOSE: To evaluate the relationship between the speed of enhancement of hepatic hemangiomas on gadolinium-enhanced MRI and ADC values by using various parameters, including the D, f, D* and ADC(fit) on intravoxel incoherent motion (IVIM) MR Imaging. MATERIALS AND METHODS: The institutional review board approved this retrospective study. A total of 47 hepatic hemangiomas from 39 patients were included (20 men and 19 women). The hemangiomas were classified into three types according to the enhancement speed of the hepatic hemangiomas on gadolinium-enhanced dynamic T1-weighted images: rapid (Type A), intermediate (Type B), and slow (Type C) enhancement. The D, f, D* and ADC(fit) values were calculated using IVIM MR imaging. The diffusion/perfusion parameters and ADC values were compared among the three types of hemangiomas. RESULTS: Both the ADC(fit) and D values of type C were significantly lower than those of type A (P = 0.0022, P = 0.0085). However, for the f and D*, there were no significant differences among the three types. On DWI with all b values (50, 200, 500 and 800 sec/mm2), the ADC values of type C were significantly lower than those of the type A (P < 0.012). For b values with 800 sec/mm2, the ADC800 values of the type C hemangiomas were significantly lower than those of type B (P = 0.0021). We found a negative correlation between hepatic hemangioma enhancement type and ADC50 (rho= -0.357, P = 0.014), ADC200 (rho= -0.537, P = 0.0001), ADC500 (rho= -0.614, P = 0.0001), and ADC800(rho= -0.607, P = 0.0001). Therefore, four ADC values of ADC50, ADC200, ADC500, and ADC800 were decreased with decreasing enhancement speed. CONCLUSION: Hepatic hemangiomas had variable ADCs according to the type of enhancement, and the reduced ADCs in slowly enhancing hemangiomas may be related to the reduced pure molecular diffusion (D).
Diffusion ; Ethics Committees, Research ; Hemangioma* ; Humans ; Magnetic Resonance Imaging* ; Male ; Retrospective Studies