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PubMedDate not supplied

Determination of 1H relaxation times of water in human bone marrow by fat-suppressed turbo spin echo in comparison to MR spectroscopic methods.

Relaxation times of water were measured in human vertebral bodies by a fat-suppressed dual-echo turbo spin echo/turbo inversion recovery MRI sequence. Comparison was made with T1 and T2 values obtained by localized 1H-MR spectroscopy. The accuracy of the results and the diagnostic potential of the fast quantitative MRI technique were evaluated in 20 volunteers, 11 patients with osteoporosis, 6 patients with lymphoma, and 6 patients with bone marrow metastasis. No significant alterations of T1 and T2 relaxation times of water and fat were found in osteoporosis. With both methods, an increase in the T1 values of the water resonance by 16% was observed in lymphomas, which was highly significant (P < .001) in the MRS measurements, and an elevation by the same amount was obtained by the MRI sequence for the metastases (P = .040). A strong reduction of fat fraction was quantified by MRS in the tumorous cases. T2 of the water resonance increased by more than 30% (P < .003) in metastases. Water T2 values obtained by the MRI sequence showed systematic deviations from the MRS results, especially at short echo spacings.

Adipose Tissue↗
PubMedDate not supplied

MRI diagnosis and follow-up of subcutaneous fat necrosis.

The purpose of this report is to present the MRI features of subcutaneous fat necrosis (SFN) and the natural history of this process. We have seen 12 patients with SFN, one case of which was confirmed histopathologically. In six patients, a follow-up MRI study was performed. MRI findings were very similar in all of the cases: small, linear, and spiculated lesions with one or two components: a globular area yielding high signal intensity on T1-weighted images, intermediate to high signal intensity on fast SE T2-weighted images and focal signal void on short-inversion -time inversion recovery (STIR) sequence, corresponding to an area of fat necrosis; and a laminar starred component, with low signal intensity on T1 and fast SE T2-weighted images and high signal intensity on the STIR sequence, corresponding to reactive fibrous tissue. The follow-up MRI study of six patients showed either disappearance (n = 2) or decrease in size (n = 3) of the globular component; in one patient, no change was observed. A less prominent decrease of the laminar component also was seen in five patients. One patient did not present any change in this laminar component. The most characteristic MRI findings of this lesion are the high signal intensity areas on T1-weighted images, their small size (< 3 cm), their linear spiculated shape with both laminar and globular components, and no contrast enhancement after injection of gadolinium-diethylenetriamine pentaacetic acid (Gd-DTPA) injection. We believe that the location, size, morphology, and MRI signal intensity of SFN may allow its differentiation from other types of soft tissue lesions.

Adolescent↗
PubMedDate not supplied

Interactive MRI-guided radiofrequency interstitial thermal ablation of abdominal tumors: clinical trial for evaluation of safety and feasibility.

This clinical trial was performed to evaluate the safety and feasibility of interactive MR-guided radiofrequency (RF) interstitial thermal ablation (ITA) performed entirely within the MR imager. RF-ITA was performed on 11 intra-abdominal metastatic tumors during 13 sessions. The RF electrode was placed under MR guidance on a .2-T system using rapid fast imaging with steady state precession (FISP) and true FISP images. A custom 17-gauge electrode was used and was modified in four sessions to allow circulation of iced saline for cooling during ablation. Tissue necrosis monitoring and electrode repositioning were based on rapid T2-weighted and short-inversion-time inversion recovery (STIR) sequences. Morbidity and toxicity were assessed by clinical and imaging criteria. The region of tissue destruction was visible in all 11 tumors treated, as confirmed on subsequent contrast-enhanced images. No significant morbidity was noted, and patient discomfort was minimal. In conclusion, interactive MR-guided RF-ITA is feasible on a clinical .2-T C-arm system with supplemental interventional accessories with only minor patient morbidity. The ability to completely ablate tumors with RF-ITA depends on tumor size and vascularity.

Abdominal Neoplasms↗
PubMed2004

Three-dimensional magnetic resonance imaging technique for myocardial-delayed hyperenhancement: a comparison with the two-dimensional technique.

PURPOSE: To compare two-dimensional and three-dimensional techniques in the detection of myocardial infarction (MI) and in the grading transmural extent (TE). MATERIALS AND METHODS: Twelve patients with clinically proven MI were examined using two-dimensional and three-dimensional techniques with cardiac-gated, breath-hold, T1-weighted gradient echo sequence with an inversion recovery pulse following gadopentetate dimeglumine (Gd-DTPA) at 0.2 mmol/kg. Contrast-to-noise, signal-to-noise, and signal intensity ratios (CNR, SNR, and SIR, respectively) were derived and compared for each technique. RESULTS: From two-dimensional to three-dimensional, statistical significant difference was found in the mean CNR (11.65 vs. 56.59; P = 0.002), SNR (18.03 vs. 76.90; P < 0.001), and SIR (3.6 vs. 6.36; P = 0.05). Intraobserver agreement (kappa) between two-dimensional and three-dimensional were R1 = 74% and R2 = 90%. Interobserver agreements between the readers were two-dimensional = 77% and three-dimensional = 79%. CONCLUSION: Mean CNR, SNR, and SIR are significantly increased in the three-dimensional technique compared to the conventional two-dimensional technique.

Adult↗
PubMed2005

Conspicuity of liver hemangiomas: short tau inversion recovery, T1, and T2 imaging with gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid.

PURPOSE: To compare conspicuity of liver hemangiomas on STIR, T1-weighted, and T2-weighted magnetic resonance (MR) images before and after administration of gadolinium ethoxybenzyl diethylenetriaminepentaacetic acid (Gd-EOB-DTPA) (hepatocellular contrast agent), using contrast-to-noise ratios (CNRs). MATERIALS AND METHODS: Thirteen hemangiomas were imaged using breath-hold gradient echo (GRE) T1, fat-saturated turbo spin echo (TSE)-T2, and short tau inversion recovery (STIR) sequences. Background noise and signal-to-noise ratios (SNRs) for liver and hemangioma, along with CNR for normal liver and hemangioma, were measured on each sequence before and after administration of Gd-EOB-DTPA. Hemangioma conspicuity was also evaluated qualitatively. RESULTS: After Gd-EOB-DTPA administration, the quantitative liver SNR decreased 54% on STIR, increased 45% on T1-weighted images, and increased 14.5% on TSE-T2-weighted images. The CNR for liver and hemangioma increased 50% on STIR images (P < 0.0001), increased 46% on T1-weighted imaging (P = 0.0033), and increased 22% on TSE-T2-weighted MR imaging (MRI) (P = 0.0083). After contrast, the CNR for TSE-T2 images was greater than those for both the T1 and STIR images (P < 0.0001 for both). Qualitatively, signal change was visually apparent in the liver on T1 and STIR, but not on T2 images or in the hemangiomas on any sequence. CONCLUSION: Despite the statistically significant T1 and STIR increase in CNR, liver hemangiomas were most conspicuous on TSE-T2 images after Gd-EOB-DTPA. This pilot study with hemangiomas highlights the newly recognized potential benefit of TSE-T2 imaging with hepatocellular contrast.

Adult↗
PubMed2006

Comparison of the magnetization transfer ratio and fluid-attenuated inversion recovery imaging signal intensity in differentiation of various cystic intracranial mass lesions and its correlation with biological parameters.

PURPOSE: To compare the signal intensity on the fluid attenuated inversion recovery (FLAIR) sequence and magnetization transfer ratios (MTRs) for the differentiation of abscesses from non-abscess cystic brain lesions, and to correlate these MR parameters with the viscosity, viable cell density and total protein concentration of the cystic fluid. MATERIALS AND METHODS: Signal intensity on FLAIR and MTRs from the cystic cavity of lesions were calculated from 33 patients (brain abscess (N = 12) and non-abscess (N = 21)). The fluid from the lesion was aspirated at the time of surgery, and the viscosity, viable cell density, and total protein concentration were measured. RESULTS: Signal intensity on FLAIR correlated significantly with the total protein concentration in abscess (r = 0.60, P < 0.05) and non-abscess lesions (r = 0.41, P < 0.05). However, there was no significant difference (P > 0.05) in the FLAIR signal intensity of the abscess (318.8 +/- 75) and non-abscess group (258 +/- 47). The MTR of the brain abscesses (13 +/- 0.95) was significantly higher (P < 0.05) than that of the non-abscess group (3.5 +/- 0.3). A significant correlation was observed between MTR and viscosity (r = 0.75, P < 0.05), total protein concentration (r = 0.60, P < 0.05), and cell density (r = 0.70, P < 0.05) in brain abscess, and viscosity (r = 0.81, P < 0.05) and total protein concentration (r = 0.41, P < 0.05) in non-abscess lesions. CONCLUSION: It is possible to differentiate brain abscesses from non-abscess cystic lesions using MT imaging. The MTR correlates significantly with the viscosity, viable cell density, and total protein concentration in brain abscess, and with viscosity and total protein concentration in non-abscess lesions. FLAIR signal intensity correlates significantly only with the total protein concentration in abscess and non-abscess lesions.

Adolescent↗
PubMed2003

Performance of a new gadolinium-based intravascular contrast agent in free-breathing inversion-recovery 3D coronary MRA.

In three-dimensional (3D) coronary magnetic resonance angiography (MRA), the in-flow contrast between the coronary blood and the surrounding myocardium is attenuated as compared to thin-slab two-dimensional (2D) techniques. The application of a gadolinium (Gd)-based intravascular contrast agent may provide an additional source of signal and contrast by reducing T(1blood) and supporting the visualization of more distal or branching segments of the coronary arterial tree. In six healthy adults, the left coronary artery (LCA) system was imaged pre- and postcontrast with a 0.075-mmol/kg bodyweight dose of the intravascular contrast agent B-22956. For imaging, an optimized free-breathing, navigator-gated and -corrected 3D inversion recovery (IR) sequence was used. For comparison, state-of-the-art baseline 3D coronary MRA with T(2) preparation for non-exogenous contrast enhancement was acquired. The combination of IR 3D coronary MRA, sophisticated navigator technology, and B-22956 allowed for an extensive visualization of the LCA system. Postcontrast, a significant increase in both the signal-to-noise ratio (SNR; 46%, P < 0.05) and contrast-to-noise ratio (CNR; 160%, P < 0.01) was observed, while vessel sharpness of the left anterior descending (LAD) artery and the left coronary circumflex (LCX) were improved by 20% (P < 0.05) and 18% (P < 0.05), respectively.

Adult↗
PubMed2004

Artifact suppression in imaging of myocardial infarction using B1-weighted phased-array combined phase-sensitive inversion recovery.

Regions of the body with long T1, such as cerebrospinal fluid (CSF), may create ghost artifacts on gadolinium-hyperenhanced images of myocardial infarction when inversion recovery (IR) sequences are used with a segmented acquisition. Oscillations in the transient approach to steady state for regions with long T1 may cause ghosts, with the number of ghosts being equal to the number of segments. B1-weighted phased-array combining provides an inherent degree of ghost artifact suppression because the ghost artifact is weighted less than the desired signal intensity by the coil sensitivity profiles. Example images are shown that illustrate the suppression of CSF ghost artifacts by the use of B1-weighted phased-array combining of multiple receiver coils.

Artifacts↗
PubMed1991

Quantitative determination of the partial oxygen pressure in the vitrectomized rabbit eye in vivo using 19F NMR.

We have quantitatively determined the PO2 within the vitreous space of the vitrectomized rabbit eye in vivo using 19F NMR and perfluorotributylamine (FTBA). The results of the present work are in good agreement with previous measurements of PO2 within the nonvitrectimized rabbit eye obtained using oxygen microelectrodes. In this study, good precision and accuracy were achieved by: (1) having minimal flow effects present, (2) optimizing the signal-to-noise through the use of neat FTBA and surface coil transmission and detection, and (3) performing an inversion-recovery pulse sequence, with adiabatic pulses, to optimize the dynamic range of the T1 experiment. Possible deleterious effects on the measured T1 due to the vitreal temperature gradient are discussed. To the best of our knowledge the results of this study demonstrate, for the first time, a quantitative determination of intraocular PO2 in vivo using 19F NMR and FTBA.

Animals↗
PubMed1991

Pulsed NMR relaxometry of striated muscle fibers.

The longitudinal (T1) and transverse (T2) proton (1H) nuclear magnetic resonance (NMR) relaxation of fast- and slow-twitch muscle fibers are examined using rat muscle tissues in which one fiber type predominates. Both continuum and discrete exponential component fits are made to Carr-Purcell-Meiboom-Gill (CPMG) and inversion recovery pulse sequence measurements. In addition, experiments which illustrate the large sources of variability that have led to apparent conflicts in the literature are presented. Based on the results of this study, unique NMR features that distinguish fast- and slow-twitch muscle fibers are presented. The feasibility of differentiating fast- and slow-twitch muscle fibers using magnetic resonance (MR) imaging is briefly discussed.

Analysis of Variance↗
PubMed1992

Effects of local irradiation on spin-lattice relaxation time of phosphate metabolites in mouse tumors monitored by 31P magnetic resonance spectroscopy.

An inversion-recovery pulse sequence and solenoidal surface coil were employed to determine the spin-lattice relaxation time (T1) in murine tumors (RIF-1 and SCCVII). Reduction in T1s of inorganic phosphate (Pi) and nucleotide triphosphates (NTP) has been observed in irradiated tumors compared with unirradiated tumors. The reduction is accompanied by tumor regression and improved tumor energetic status in both tumor lines. The results of the T1 measurement of phosphate metabolites in tumors suggest that partial saturation effects may exist in spectra and could effect quantitative analysis when short repetition time is used. The reduction in T1s of Pi and NTP may be attributed to the active biochemical exchange and better tumor oxygenation in irradiated tumors.

Animals↗
PubMed2004

Simultaneous MRI acquisition of blood volume, blood flow, and blood oxygenation information during brain activation.

Simultaneous acquisition of complementary functional hemodynamic indices reflecting different aspects of brain activity would be a valuable tool for functional brain-imaging studies offering enhanced detection power and improved data interpretation. As such, a new MRI technique is presented that is able to achieve concurrent acquisition of three hemodynamic images based primarily on the changes of cerebral blood volume, blood flow, and blood oxygenation, respectively, associated with brain activation. Specifically, an inversion recovery pulse sequence has been designed to measure VASO (vascular space occupancy), ASL (arterial spin labeling) perfusion, and BOLD (blood-oxygenation-level-dependent) signals in a single scan. The MR signal characteristics in this sequence were analyzed, and image parameters were optimized for the simultaneous acquisition of these functional images. The feasibility and efficacy of the new technique were assessed by brain activation experiments with visual stimulation paradigms. Experiments on healthy volunteers showed that this technique provided efficient image acquisition, and thus higher contrast-to-noise ratio per unit time, compared with conventional techniques collecting these functional images separately. In addition, it was demonstrated that the proposed technique was able to be utilized in event-related functional MRI experiments, with potential advantages of obtaining accurate transient information of the activation-induced hemodynamic responses.

Blood Flow Velocity↗
PubMed2006

Fast perfusion measurements in rat skeletal muscle at rest and during exercise with single-voxel FAIR (flow-sensitive alternating inversion recovery).

Non-invasive measurement of perfusion in skeletal muscle by in vivo magnetic resonance remains a challenge due to its low level and the correspondingly low signal-to-noise ratio. To enable accurate, quantitative, and time-resolved perfusion measurements in the leg muscle, a technique with a high sensitivity is required. By combining a flow-sensitive alternating inversion recovery (FAIR)-sequence with a single-voxel readout, we have developed a new technique to measure the perfusion in the rat gastrocnemius muscle at rest, yielding an average value of 19.4 +/- 4.8 mL/100 g/min (n = 22). In additional experiments, perfusion changes were elicited by acute ischemia and reperfusion or by exercise induced by electrical, noninvasive muscle stimulation with varying duration and intensity. The perfusion time courses during these manipulations were measured with a temporal resolution of 2.2 min, showing increases in perfusion of a factor of up to 2.5. In a direct comparison, the results agreed closely with values found with microsphere measurements in the same animals. The quantitative and noninvasive method can significantly facilitate the investigation of atherosclerotic diseases and the examination of drug efficacy.

Animals↗
PubMed2006

Mice with a deletion in the first intron of the Col1a1 gene develop dissection and rupture of aorta in the absence of aneurysms: high-resolution magnetic resonance imaging, at 4.7 T, of the aorta and cerebral arteries.

Deletion of the majority of the first intron of the Col1a1 gene in mice leads to decreased type I collagen synthesis and content in the aortic wall. In 54% of cases, mice homozygous for the Col1a1 mutation die of thoracic hemorrhage by the age of 18 months. It is unknown whether the fatal bleeding results from an acute dissection of the aortic wall or a gradually developing dilatation of the medial layer prior to rupture. We optimized high-resolution MRI methods using a 4.7 T MR scanner to obtain in vivo images of the entire mouse aorta. The MR images were acquired in three imaging planes using gradient echo, spin echo, and spin echo with inversion recovery pulse sequences with a maximum in-plane resolution of 68 x 68 microm and acquisition times less than 10 min. In five Col1a1 mutated mice aged 16 months, the MR images showed no signs of aneurysmal dilatation, wall defects, or former dissection, suggesting that the mechanism for aortic rupture is an acute dissection of the aortic medial layer. Cerebral arteries were imaged using a three-dimensional time of fight pulse sequence. The resolution of 73 x 73 x 94 microm showed normal cerebral arteries. Histology showed a 22% thinner cerebral artery wall in Col1a1 mutated mice.

Animals↗
PubMed1995

Isolated femoral mononeuropathy to the vastus lateralis: EMG and MRI findings.

A 16-year-old female track athlete experienced sudden onset of right anterolateral thigh pain, initially thought to be cramping. After 2 months of continued postexercise pain she sought medical evaluation. A 3-cm thigh circumference discrepancy was noted on physical exam. She was referred for electromyography (EMG) and magnetic resonance imaging (MRI) studies. Femoral and screening nerve conduction studies were normal. Needle EMG revealed acute neuropathic changes confined to the right vastus lateralis only. These findings were confirmed by MRI, including short T1 inversion recovery (STIR) sequences. All other medical work-up was normal, including lumbar and pelvic MRI, and complete serologic studies. This case represents a unique presentation of an idiopathic femoral mononeuropathy isolated to the vastus lateralis only, which has not been previously reported. The highly unusual anatomical presentation of this case illustrates the emerging complementary usefulness of EMG and MRI in delineating neuromuscular pathology.

Action Potentials↗
PubMed1995

Investigating a sequence of randomized phase II trials to discover promising treatments.

We consider clinical trial strategies to study diseases in which there is rapidly developing technology. We assume the availability of a limited number of patients for screening treatments over a time horizon, and that availability of new treatments for test is staggered over time. We assume further that patient response is binary and rapidly observable. We consider the strategy of conducting a sequence of two-armed randomized clinical trials. We carry over the treatment with the larger number of observed successes on the current trial to the next trial for comparison with a new treatment, with this process repeated at each step. For a fixed total number of patients (N), the number of trials one may conduct in sequence (k) is inversely related to the sample size per trial (2n), N = 2nk. We investigate how k and n influence (a) the expected success probability for the treatment selected at the end, and (b) the expected number of total successes for the N patients. The ultimate objective is to select one treatment, the winner at stage k, to test against a standard regimen in a randomized comparative phase III trial.

Clinical Trials, Phase II as Topic↗
PubMed1998

High-resolution MRI of intact and transected rat spinal cord.

Spinal cord transection at midthoracic level leads to an immediate loss of hindlimb motor function as well as to a progressive degeneration of descending and ascending spinal cord pathways. Thoracic spinal cord in unlesioned control rats and in rats 2 to 6 months after complete midthoracic transection were imaged in vivo using an ultrahigh-field (4.7 T) magnetic resonance spectrometer. High-resolution spin-echo and inversion-recovery pulse sequences were employed. In addition, the apparent diffusion coefficients (ADCs) in longitudinal and transverse directions of the spinal cord were determined. Anatomical MRI findings were confirmed in histological spinal cord tissue preparations. In healthy spinal cord, gray and white matter were easily discerned in proton density-weighted images. An infield resolution of max. 76 micrometers per pixel was achieved. In animals with chronic spinal cord transection changes in gray-white matter structure and contrast were observed toward the cut end. The spinal cord stumps showed a tapering off. This coincided with changes in the longitudinal/transverse ADC ratio. Fluid-filled cysts were found in most cases at the distal end of the rostral stump. The gap between the stumps contained richly vascularized scar tissue. Additional pathologic changes included intramedullary microcysts, vertebral dislocations, and in one animal compression of the spinal cord. In conclusion, MRI was found to be a useful method for in vivo investigation of anatomical and physiological changes following spinal cord transection and to estimate the degree of neural degeneration. In addition, MRI allows the description of the accurate extension of fluid spaces (e.g., cysts) and of water diffusion characteristics which cannot be achieved by other means in vivo.

Animals↗
PubMed1998

Measurement of Chemical Exchange Rate Constants with Solvent Protons Using Radiation Damping

When chemical exchange occurs between a concentrated and a diluted species like the proton exchange between water and proteins in biochemical systems, it is difficult to use the conventional methods for a quantitative dynamical study. In this paper, a new approach which utilizes radiation damping of the strong water magnetization exchanging with the weak resonance of the mobile protons in biomolecules is proposed. It is demonstrated with a dilute guanidine solution, using the simple inversion-recovery pulse sequence, that the exchange rate constants between water and guanidine protons are evaluated by solving the Bloch equations modified with both the radiation damping and the chemical exchange effects. Copyright 1998 Academic Press.

Journal Article↗