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PubMed1985

Theoretical considerations for optimizing intensity differences between primary musculoskeletal tumors and normal tissue with spin-echo magnetic resonance imaging.

In the radiographic assessment of primary musculoskeletal tumors, it is important for therapy planning to accurately define the extent of a tumor. Using a double spin-echo pulse sequence, the T1 and T2 relaxation times and relative hydrogen densities of several neoplastic tissues and of several normal tissues in four patients were measured. Neoplasms measured included one fibrosarcoma, two osteosarcomas, and one giant cell tumor. Normal tissues measured included normal muscle, fat, and bone marrow. Using a mathematical model of the double spin-echo pulse sequence, the intensity difference between each tumor and each normal tissue for multiple values of TR and TE was calculated. These calculated intensity differences were then used to plot isodifference contour curves for each tissue pair. These plots enabled us to pick combinations of TR and TE that optimized the signal difference between tumor and normal tissue. When comparing tumor with predominantly fatty tissue such as marrow or subcutaneous fat, optimal signal difference in our imager occurred at a TR of 600 to 800 msec and a very short TE. When comparing tumor with muscle, optimal signal difference occurred with very long TR times, and TE times ranging from 30 to 90 msec. These preliminary results suggest that an optimal scanning protocol for primary musculoskeletal tumors should contain at least two different pulse sequences with widely separated TR values (500 and 2000 msec in our instrument), and short to intermediate values of TE (28 and 56 msec in our instrument). It is believed that analysis of isodifference contour plots is a useful method for optimizing intensity differences between any two tissue types.

Bone Neoplasms↗
PubMed1999

Volume (three-dimensional) fast spin-echo imaging of the lumbar spine.

RATIONALE AND OBJECTIVES: The purpose of this study was to prospectively evaluate a proton-density-weighted, three-dimensional (3D) volume fast spin-echo (SE) pulse sequence in the assessment of the lumbar spine for suspected spondylosis. MATERIALS AND METHODS: Twenty-eight patients referred for low back or lower extremity pain were imaged with both a two-dimensional (2D) protocol and a proton-density-weighted 3D volume fast SE imaging. The spinal canal, conus medullaris, intervertebral disks, neural foramina, bone marrow, and spinal alignment shown with the 3D volume fast SE pulse sequence were independently assessed by two neuroradiologists. These findings were compared with those of the routine 2D studies. RESULTS: Interpretation of disk protrusions and stenoses of the neural foramina were concordant between both protocols. No instance of cord abnormality was detected with either protocol. CONCLUSION: A 3D volume fast SE proton-density-weighted pulse sequence may provide information comparable to that of routine 2D imaging. Advantages of volume imaging include thinner sections, the capability of reconstruction into any plane, and the potential to decrease imaging time.

Adult↗
PubMed1991

New spatial localization method using pulsed high-order field gradients (SHOT: Selection with High-Order gradienT).

A new spatial localization method using an additional set of high-order magnetic field gradients is described. The method uses a nonlinear part of high-order magnetic field gradient patterns which allows us to select a volume in conjunction with the selective radiofrequency (RF) pulse. Unlike the other existing volume selection methods such as ISIS or SPARS, the proposed selection method requires only one RF-gradient pulse pair to select a volume in two directions. The center of the selected volume can be moved to any arbitrary location within the body by the addition of precalculated lower order gradients which are simultaneously pulsed with the high-order gradient. The method also has the potential for localized spectroscopy from the FID signal which can be realized by using oscillating second- and first-order gradients for 3D selection with a single RF pulse. By using the proposed localization method, it is possible to design more flexible pulse sequences, e.g., the shorter echo-time spectroscopic pulse sequence. We have designed and constructed a six-loop r2 (or x2 + y2) gradient coil for initial application. By simultaneously applying this second-order gradient and proper x, y, and/or z gradients, 2D selections were achieved in arbitrarily selected positions in conjunction with a single selective RF pulse. Phantom and animal experiments have been performed and the results appear promising, especially in areas of NMR spectroscopic imaging applications where spatial localization is essential.

Animals↗
PubMedDate not supplied

Rapid T2-weighted MR imaging of uterine leiomyoma and adenomyosis.

BACKGROUND: To compare three rapid T2-weighted pulse sequences with high-resolution turbo spin-echo (SE) magnetic resonance (MR) imaging for the diagnosis of leiomyoma and adenomyosis. METHODS: Eighteen patients referred for evaluation of suspected leiomyoma or adenomyosis underwent imaging at 1.5 T with a phased-array multicoil. Non-breath-hold, fat-saturated sagittal images of 4-7 mm, with equivalent voxel size, were obtained through the pelvis with the following three rapid pulse sequences: segmented, half-Fourier single shot turbo SE (HASTE), turboGRASE (TGSE) and turbo SE MR images. Mean acquisition times were 17 s (HASTE), 37 s (TGSE), and 42 s (turbo SE). These images were compared, in a blinded fashion, to high resolution turbo SE MR images, which are considered the "standard" for pelvic MRI. RESULTS: The three rapid pulse sequences, HASTE, TGSE and turbo SE, provided equivalent diagnostic information when compared with high-resolution turbo SE MR images. There was no significant difference in image quality, detection and localization of leiomyoma or in diagnosis of adenomyosis among the three rapid sequences. HASTE imaging demonstrated the least ghosting. CONCLUSION: Diagnostic T2-weighted images of benign uterine pathology may be obtained in as little as 17 s.

Adult↗
PubMed1994

A general enhancement scheme in heteronuclear multidimensional NMR employing pulsed field gradients.

General pulse sequence elements that achieve sensitivity-enhanced coherence transfer from a heteronucleus to protons of arbitrary multiplicity are introduced. The building blocks are derived from the sensitivity-enhancement scheme introduced by Cavanagh et al. ((1991) J. Magn. Reson., 91, 429-436), which was used in conjunction with gradient coherence selection by Kay et al. ((1992) J. Am. Chem. Soc., 114, 10663-10665), as well as from a multiple-pulse sequence effecting a heteronuclear planar coupling Hamiltonian. The building blocks are incorporated into heteronuclear correlation experiments, in conjunction with coherence selection by the formation of a heteronuclear gradient echo. This allows for efficient water suppression without the need for water presaturation. The methods are demonstrated in HSQC-type experiments on a sample of a decapeptide in H2O. The novel pulse sequence elements can be incorporated into multidimensional experiments.

Amino Acid Sequence↗
PubMed2005

Heterodyned fifth-order 2D-IR spectroscopy of the azide ion in an ionic glass.

A heterodyned fifth-order infrared pulse sequence has been used to measure a two-dimensional infrared (2D-IR) spectrum of azide in the ionic glass 3KNO3:2Ca(NO3)2. By rephasing a two-quantum coherence, a process not possible with third-order spectroscopy, the 2D-IR spectra are line narrowed, allowing the frequencies, anharmonicities, and their correlations to be measured for the first four (nu=0-3) antisymmetric stretch vibrational levels. In this glass, the vibrational levels are extremely inhomogeneously broadened. Furthermore, the glass shifts the energy of the nu=3 state more than the others, causing an inhomogeneous distribution in the anharmonic constants that are partially correlated to the inhomogeneous distribution of the fundamental frequency. These effects are discussed in light of the strong interactions that exist between the charged solute and solvent. Since this is the first example of a heterodyned fifth-order infrared pulse sequence, possible cascaded contributions to the signal are investigated. No evidence of cascaded signals is found. Compared to third-order spectroscopies, fifth-order pulse sequences provide advanced control over vibrational coherence and population times that promise to extend the capabilities of ultrafast infrared spectroscopy.

Journal Article↗
PubMed1996

[FLAIR images of subarachnoid hemorrhage].

We studied MR fluid attenuated inversion recovery (FLAIR) pulse sequences in 37 cases with subarachnoid hemorrhage caused by aneurysmal rupture. FLAIR sequence suppressed the CSF signal and produced very heavy T2 weighted images. This has been of particular benefit in identifying lesions at the margins of the brain, around the basal cisterns, in the brain stem and at the gray-white matter junction. Based on these findings, we were able to detect the subarachnoid hemorrhage. Subarachnoid hemorrhage was able to be demonstrated as high signal intensity on FLAIR sequences in all patients. Clear visualization of acute subarachnoid hemorrhage was able to be obtained by MR FLAIR sequences in not only Fisher's group 3 or 4, but also Fisher's group 2. Moreover it was suited for the detection of intraaxial hematoma, Sylvian hematoma, subdural hematoma and subarachnoid hemorrhage in the posterior fossa and interhemispheric fissure. Especially, it was useful for detecting intraventricular hemorrhage. Therefore, if patients suffering from subarachnoid hemorrhage present slight headache or atypical symptoms, sometimes it may be more suitable to perform MRI FLAIR pulse sequences first. Aneurysms were found in 21 cases (56.8%). When the aneurysmal size is more than 7 mm, the rate of detection becomes 100%. Aneurysms present various MR appearances because of flow characteristics. Aneurysms were demonstrated as low signal intensity except in 3 cases. In one out of 3 cases, aneurysms were revealed as high signal intensity and in the other two cases, it was revealed as mixed signal intensity. According to the previous studies, rapid flow was demonstrated as low signal intensity by vascular flow void, and delayed flow was demonstrated as high or mixed signal intensity by flow related enhancement and even echo rephasing. MR clearly delineates the size, the lumen, the flow, and the extraaxial location of aneurysms. In conclusion, MR FLAIR pulse sequences could be reliable and useful for diagnosis of subarachnoid hemorrhage, especially as screening tests for outpatients.

Adult↗
PubMed1999

Band-selective HSQC and HMBC experiments using excitation sculpting and PFGSE.

Variants of the HSQC and HMBC experiments are described. They allow the restriction of the heteronuclear chemical shift domain without causing spectral folding. Selectivity is introduced in the HSQC experiment by means of excitation sculpting. The selective element of the pulse sequence is a double pulsed field gradient spin echo. It may be used either split by the t(1) evolution period, or not. The selectivity profile depends on the scheme used as well as on the number of protons attached to the heteronucleus. The selective HMBC experiment requires only a single echo sequence as no strict control of the signal phase is required. A complex glycoconjugate is used as a test compound for the new pulse sequences.

Magnetic Resonance Spectroscopy↗
PubMed1994

Blood flow dynamics in the vertebrobasilar system: correlation of a transparent elastic model and MR angiography.

PURPOSE: To describe the flow patterns in a model of the vertebrobasilar artery and use these observations to explain the appearance of the flow on the MR images. METHODS: We created an anatomically precise, transparent elastic model of the human vertebrobasilar artery containing a basilar tip aneurysm and perfused the model with non-Newtonian fluid which has similar rheologic properties to blood. Flow patterns in the vessels were directly observed. MR angiogram images were obtained with commercially available two-dimensional time-of-flight, three-dimensional time-of-flight, and 3-D phase-contrast MR angiographic pulse sequences, and they were correlated with the directly seen flow patterns. Quantitative flow velocity measurements were performed with 2-D cine phase-contrast MR angiography and correlated with the flow measured with an electromagnetic flow meter. RESULTS: Visualization studies showed the dye stream patterns in the vertebrobasilar arteries to be extremely complex and variable. During the MR experiments we found that often the same segment of a vessel could appear very different depending on the pulse sequence. In some instances, the model experiments helped to explain the MR appearance of the vessels. Flow profiles measured with 2-D cine phase contrast were found to be consistent with those measured directly with an electromagnetic flow meter. CONCLUSION: Clear elastic models can be used to duplicate the flow in human cranial vessels and thus provide a unique means to observe these flow patterns directly. The flow patterns helped to explain the variation in appearance of the vessels and the artifacts with different MR angiography pulse sequences. The artifacts depend on both the geometry of the vessel and the flow pattern within it. Two-dimensional cine phase-contrast MR provides temporal flow field information that is directly related to physiological information about flow volumes and velocity patterns.

Adult↗
PubMed2002

Three-dimensional spiral MR imaging: Application to renal multiphase contrast-enhanced angiography.

A fast MR pulse sequence with spiral in-plane readout and conventional 3D partition encoding was developed for multiphase contrast-enhanced magnetic resonance angiography (CE-MRA) of the renal vasculature. Compared to a standard multiphase 3D CE-MRA with FLASH readout, an isotropic in-plane spatial resolution of 1.4 x 1.4 mm(2) over 2.0 x 1.4 mm(2) could be achieved with a temporal resolution of 6 sec. The theoretical gain of spatial resolution by using the spiral pulse sequence and the performance in the presence of turbulent flow was evaluated in phantom measurements. Multiphase 3D CE-MRA of the renal arteries was performed in five healthy volunteers using both techniques. A deblurring technique was used to correct the spiral raw data. Thereby, the off-resonance frequencies were determined by minimizing the imaginary part of the data in image space. The chosen correction algorithm was able to reduce image blurring substantially in all MRA phases. The image quality of the spiral CE-MRA pulse sequence was comparable to that of the FLASH CE-MRA with increased spatial resolution and a 25% reduced contrast-to-noise ratio. Additionally, artifacts specific to spiral MRI could be observed which had no impact on the assessment of the renal arteries.

Adult↗
PubMed2004

Brain GABA editing by localized in vivo (1)H magnetic resonance spectroscopy.

Editing of GABA by (1)H MRS in a specific brain area is a unique tool for in vivo non-invasive investigation of neurotransmission disorders. Selective GABA detection is achieved using sequences based on double quantum coherence (DQC). Our pulse sequence makes accurate measurements without artefacts due to spatial localization. The sequence was tested on a phantom solution. The effect of vigabatrin, a specific inhibitor of GABA transaminase, was measured in rat brain and GABA detection was performed in vivo in monkey brain using this procedure. Rats were split into two groups. In the control group, the rats had access to water and, in the other group (vigabatrin, VGB, rats), animals were allowed free access to drinking water containing vigabatrin. After 3 weeks of treatment, rats were anesthetized for in vivo NMR spectroscopy investigation. At the end of the experiment, brains were quickly removed, freeze-clamped and extracted with 4% perchloric acid. One part of the acid extract was used for GABA concentrations assessment by ion exchange chromatography with ninhydrin detection. The second was used for high-resolution NMR analysis. By chromatography measurements, the GABA concentration was 1.23+/-0.06 micromol/g for controls, while for vigabatrin-treated rats the GABA concentration was 4.89+/-1.60 micromol/g. The NMR in vivo results were closely correlated with the NMR ex vivo (r=0.99, p<0.01) and chromatography results (r=0.98, p<0.01). The correlation between ex vivo results and chromatography results was also high (r=0.99, p<0.001). This pulse sequence performed GABA editing from a 376 microl voxel located on the right basal ganglia area in a non-human primate brain. This in vivo GABA editing scheme can thus be proposed for accurate measurement of brain GABA concentrations.

Administration, Oral↗
PubMed1997

Assessing contrast on MR images.

Magnetic resonance imaging pulse sequences are frequently judged by their ability to facilitate discrimination between pathologic and normal tissue. Objective analysis is usually based on signal intensity measurements. However, the literature shows disagreement as to how this analysis should be performed. The ability to visually differentiate two objects on the basis of signal intensity depends on the contrast-to-noise ratio (CNR). This parameter, however, can be calculated only by measuring the intensity of photons reaching the eye from two distinct objects and, hence, is display dependent. The signal difference-to-noise ratio (SDNR) is a display-independent parameter that reflects the contrast-generating ability of a pulse sequence. When comparing two imaging sequences, the SDNR is proportional to the CNR, assuming the images being compared are displayed so that corresponding regions have the same intensity (i.e., photon fluxes). Because the SDNR is display independent, it should be the preferred parameter for assessing the contrast-generating ability of a pulse sequence. The value and limitations of these parameters are discussed.

Humans↗
PubMed2006

Cardiorespiratory-resolved magnetic resonance imaging: measuring respiratory modulation of cardiac function.

A technique for cardiac- and respiratory-resolved MRI is described. A retrospectively gated-segmented acquisition scheme similar to that used in conventional cine cardiac imaging was used to collect image data that spanned both the cardiac and respiratory cycles. Raw k-space data were regridded in a cardiorespiratory phase space to allow image reconstruction at target cardiac and respiratory phases. The approach can be applied with various k-space trajectories and pulse sequences, and was implemented in this study with both a Cartesian steady-state free precession (SSFP) sequence and a radial phase-contrast (PC) pulse sequence. Free-breathing short-axis SSFP images of the heart were reconstructed at multiple respiratory and cardiac phases to illustrate separation of cardiac and respiratory motion without artifacts. A respiratory-resolved radial PC experiment was used to quantify the volumetric flow rates in the inferior vena cava (IVC), pulmonary artery (PA), and aorta (Ao) in five free-breathing normal volunteers and a positive-pressure ventilated dog. Total flow (ml/min) in each vessel was quantified as a function of respiratory phase (peak/minimum output = 1.85 +/- 0.29 (IVC), 1.36 +/- 0.15 (PA), 1.24 +/- 0.09 (Ao)). Peak flow occurred during inspiration for the IVC and PA, and during expiration for the Ao, and there was a complete pattern reversal for the positive-pressure ventilated dog.

Adult↗
PubMed1994

A proton nuclear magnetic resonance study of the mobile regions of human erythroid spectrin.

The effect of added NaCl (0-150 mM) and temperature (6-65 degrees C) on the conformation of erythrocyte spectrin was investigated using 400 MHz 1H NMR. The relatively narrow resonances (20-40 Hz linewidth) in the spectra arising from protons in regions of the molecule undergoing rapid motions were selectively detected using either the Carr-Purcell-Meiboom-Gill (CPMG) pulse sequence without water presaturation or a simple pi/2 pulse sequence with water presaturation. The T2 relaxation of these protons was not influenced by changes in solution conditions (0-150 mM NaCl, 6-37 degrees C) indicating that their motions were independent of the overall shape of the molecule. Significant increases in the areas of the aliphatic peaks for spectrin samples at fixed salt concentrations occurred as the temperature was raised from 6 to 37 degrees C. The increases were independent of the state of polymerization of spectrin and were greater in the absence of added salt above 25 degrees C. The changes reflect increasing numbers of mobile residues, probably due to partial unfolding of spectrin's repeated structural unit. At temperatures above 37 degrees C, sharp increases in the areas of the spectral envelopes reflect cooperative unfolding of spectrin. Comparison with results previously obtained in this laboratory using CD and ORD indicate that at least part of the lost structure is alpha-helical.

Erythrocytes↗
PubMed1996

Spectral editing in 13C CP/MAS experiments at high magnetic field.

We show that the spinning side-bands of protonated and non-protonated carbon atoms can be well separated by means of the standard SCP and LCPD experiments at a relatively slow sample spinning rate or at high magnetic field. These experiments offer a promising way of measuring the principal values of chemical shift anisotropies via spinning side-band analysis in a moderately complex system. General spectral editing in 13C cross-polarization magic-angle spinning (CP/MAS) experiments at high field is achieved by incorporating the total side-band suppression (TOSS) pulse sequence into the standard series of spectral editing pulse sequences. It is confirmed that the relative signal intensity for a certain kind of functional group obtained at different polarization, polarization-inversion and depolarization times is about the same as that obtained at low magnetic field, and that the signal intensity distortion introduced by the TOSS sequence for resonances having different chemical shift anisotropies does not interfere with the spectral editing process. However, quantitative results can only be expected in those cases where full restoration of the intensity of the central band can be achieved by the TOSS sequence. This new strategy at high field is demonstrated by using fumaric acid monoethyl ester as a model compound. A typical application to a Chinese resin is presented, where the relative ratio of each functional group in the aliphatic portion to the total number of aliphatic carbon atoms is determined from only three experimental spectra.

Anisotropy↗
PubMed1999

Breath-hold 3D gadolinium-enhanced subtraction MRA in the detection of transplant renal artery stenosis.

AIMS: The purpose of this study was to assess the value of breath-hold 3D gadolinium-enhanced subtraction magnetic resonance angiography (GD-MRA) in the detection of transplant renal artery stenosis (TRAS). PATIENTS AND METHODS: Seven patients with suspected post-transplant renal artery stenosis were studied. GD-MRA was performed at 1.5T with a 3D fast spoiled gradient recalled echo (FSPGR) pulse sequence. Before injection of contrast medium, the 3D pulse sequence was performed to obtain a set of non-contrast images for subtraction purposes. Dynamic 3D imaging was performed simultaneously with the bolus injection of 40 ml of gadopentetate dimeglumine. Angiographic images were reconstructed using the Advantage Window workstation (version 2.0 GE Medical Systems) and subtraction was made with the pre-contrast image data. Any signal intensity cut-off or narrowing of more than 50% was regarded as significant stenosis. Ultrasound Doppler (USD) study was performed with both colour and spectral studies. Peak systolic velocity (PSV) of greater than 2.0 m/s and acceleration time (AT) greater than 120ms was regarded as positive for TRAS. These were then compared with the digital subtraction angiography (DSA) as the gold standard. RESULTS: A total of nine examinations performed in seven patients were included in the analysis. MRA correlated with the DSA findings in eight examinations, with one false negative. USG correlated with DSA in six examinations, with two false negative and one false positive case. CONCLUSION: In our opinion, GD-MRA is a promising and non-invasive technique in the detection of TRAS.

Adult↗
PubMed2000

Synthesis, characterization, and imaging performance of a new class of macrocyclic hepatobiliary MR contrast agents.

RATIONALE AND OBJECTIVES: To investigate the effect of substituent lipophilicity, substituent position, and overall charge on the hepatobiliary clearance and tolerance of a series of aromatic ring-containing macrocyclic Gd chelates to select a candidate compound for evaluation as a hepatobiliary imaging agent. METHODS: Hepatobiliary clearance was studied in rats. Tissue distribution and tolerance were studied in mice. Imaging was performed in cats, rabbits, and Rhesus monkeys using T1-weighted pulse sequences or T1-weighted breath-hold pulse sequences. RESULTS: All the compounds were excreted bimodally. Gd-2,5-BPA-DO3A (15d) was found to have the optimal combination of hepatobiliary clearance (47% in rats, 29% in mice) and tolerance (minimum lethal dose 5.0 mmol/kg). Initial imaging studies in cats demonstrated the feasibility of Gd-2,5-BPA-DO3A for hepatic imaging. In rabbits with implanted VX-2 adenocarcinoma as a model for metastatic liver disease, Gd-2,5-BPA-DO3A provided sustained hepatic signal intensity (SI) enhancement and lesion conspicuity over a 120-minute imaging time course. In Rhesus monkeys with normal liver function, Gd-2,5-BPA-DO3A afforded sustained hepatic SI enhancement and a time-dependent increase in gallbladder SI over the entire 90-minute imaging time course. CONCLUSIONS: Gd-2,5-BPA-DO3A provides dramatic and sustained SI enhancement of hepatic tissue in cats, rabbits, and Rhesus monkeys that was superior in all respects to the extracellular space MRI agent, Gd-HP-DO3A, that was employed as a control.

Animals↗
PubMed2005

Optimizing the automatic segmentation of the left ventricle in magnetic resonance images.

Automatic segmentation of the left ventricular (LV) myocardial borders in cardiovascular MR (CMR) images allows a significant speed-up of the procedure of quantifying LV function, and improves its reproducibility. The automated boundary delineation is usually based on a set of parameters that define the algorithms. Since the automatic segmentation algorithms are usually sensitive to the image quality and frequently depend heavily on the acquisition protocol, optimizing the parameters of the algorithm for such different protocols may be necessary to obtain optimal results. In other words, using a default set of parameters may be far from optimal for different scanners or protocols. For the MASS-software, for example, this means that a total of 14 parameters need to be optimized. This optimization is a difficult and labor-intensive process. To be able to more consistently and rapidly tune the parameters, an automated optimization system would be extremely desirable. In this paper we propose such an approach, which is based on genetic algorithms (GAs). The GA is an unsupervised iterative tool that generates new sets of parameters and converges toward an optimal set. We implemented and compared two different types of the genetic algorithms: a simple GA (SGA) and a steady state GA (2SGA). The difference between these two algorithms lies in the characteristics of the generated populations: "nonoverlapping populations" and "overlapping populations," respectively "nonoverlapping" population means that the two populations are disjoint, and "overlapping" means that the best parameters found in the previous generation are included in the present population. The performance of both algorithms was evaluated on twenty routinely obtained short-axis examinations (eleven examinations acquired with a steady-state free precession pulse sequence, and nine examinations with a gradient echo pulse sequence). The optimal parameters obtained with the GAs were used for the LV myocardial border delineation. Finally, the automatically outlined contours were compared to the gold standard--manually drawn contours by experts. The result of the comparison was expressed as a degree of similarity after a processing time of less than 72 h to a 59.5% of degree of similarity for SGA and a 66.7% of degree of similarity for 2SGA. In conclusion, genetic algorithms are very suitable to automatically tune the parameters of a border detection algorithm. Based on our data, the 2SGA was more suitable than the SGA method. This approach can be generalized to other optimization problems in medical image processing.

Algorithms↗