共查询到20条相似文献,搜索用时 234 毫秒
1.
Monitoring kidney and renal cyst volumes applying MR approaches on a rapamycin treated mouse model of ADPKD 总被引:1,自引:1,他引:0
Wilfried Reichardt Daniel Romaker Anne Becker Martin Buechert Gerd Walz Dominik von Elverfeldt 《Magma (New York, N.Y.)》2009,22(3):143-149
Object The aim of our study was to determine total cystic volume in a mouse model of PKD using MR imaging to monitor therapeutic
effects in vivo.
Materials and methods We imaged eight female pcy-mice in two groups: four belonged to an untreated control group and four were treated with the anticystic agent rapamycin,
which has proven to be effective in reducing cystogenesis in animal models. The mice were imaged using a 9.4 Tesla animal
scanner. MRI measurements were taken at six time points during the therapy. Total renal volumes and total cyst volumes were
calculated using a thresholding approach.
Results During the course of the treatment, the total cyst volume increased significantly faster than the total renal volume in the
untreated group, indicating that growth of the total renal volume in the untreated group was primarily due to the growth of
the cysts, rather than the parenchyma. The measured total renal volume in the control (placebo) group was significantly higher
than the volume in the treated group.
Conclusion Using MRI, we were able to monitor the cystic volume in a mouse model of PKD to assess the therapeutic effect of anticystic
treatment. 相似文献
2.
Herrmann KH Schmidt S Kretz A Haenold R Krumbein I Metzler M Gaser C Witte OW Reichenbach JR 《Magma (New York, N.Y.)》2012,25(3):233-244
Object
To investigate the potential of a clinical 3 T scanner to perform MRI of small rodents.Materials and methods
Different dedicated small animal coils and several imaging sequences were evaluated to optimize image quality with respect to SNR, contrast and spatial resolution. As an application, optimal grey-white-matter contrast and resolution were investigated for rats. Furthermore, manganese-enhanced MRI was applied in mice with unilateral crush injury of the optic nerve to investigate coil performance on topographic mapping of the visual projection.Results
Differences in SNR and CNR up to factor 3 and more were observed between the investigated coils. The best grey-white matter contrast was achieved with a high resolution 3D T 2-weighted TSE (SPACE) sequence. Delineation of the retino-tectal projection and detection of defined visual pathway damage on the level of the optic nerve could be achieved by using a T 1-weighted, 3D gradient echo sequence with isotropic resolution of (0.2?mm)3.Conclusions
Experimental studies in small rodents requiring high spatial resolution can be performed by using a clinical 3 T scanner with appropriate dedicated coils. 相似文献3.
Montet-Abou K Daire JL Ivancevic MK Hyacinthe JN Nguyen D Jorge-Costa M Morel DR Vallée JP 《Magma (New York, N.Y.)》2006,19(3):144-151
Object: the overall goal was to study cardiovascular function in small animals using a clinical 1.5-T MR scanner optimizing a fast gradient-echo cine sequence to obtain high spatial and temporal resolution.
Materials and methods: normal rat hearts (n = 9) were imaged using a 1.5-T MR scanner with a spiral fast gradient-echo (fast field echo for Philips scanners) sequence, three Cartesian fast gradient-echo (turbo field echo for Philips scanners) sequences with different in-plane resolution, and with and without flow compensation and half-Fourier acquisition. The hearts of four rats were then excised and left-ventricle mass was weighed. Inter- and intra-observer variability analysis was performed for magnetic resonance imaging (MRI) measurements.
Results: half-Fourier acquisition with flow compensation gave the best sequence in terms of image quality, spatial as well as temporal resolution, and suppression of flow artifact. Ejection fraction was 71 ± 4% with less than 5% inter- and intra-observer variability. A good correlation was found between MRI-calculated left-ventricular mass and wet weight.
Conclusions: using optimized sequences on a clinical 1.5-T MR scanner can provide accurate quantification of cardiac function in small animals and can promote cardiovascular research on small animals at 1.5-T 相似文献
4.
Objective: The purpose of this study was to compare the signal-to-noise ratio (SNR) of phantom and rat brain images performed at 1.5 T on a clinical MR system and at 7 T on a small-animal experimental system. Comparison was carried out by taking into account SNR values based on a single sample acquisition at 1.5 and 7 T as well as on simultaneous imaging of multiple samples at 1.5 T.
Methods: SNR was experimentally assessed on a phantom and rat brains at 1.5 and 7 T using 25 mm surface coils and compared to theoretical SNR gain estimations. The feasibility of multiple-animal imaging, using the hardware capabilities available on the 1.5 T system, was demonstrated. Finally, rat brain images obtained on a single animal at 7 T and on multiple animals acquired simultaneously at 1.5 T were compared.
Results: Experimentally determined SNR at 7 T was far below theoretical estimations. Taking into account chemical shift, susceptibility artifacts and modifications of T1 and T2 relaxation times at higher field, a 7-T system holds limited advantage over a 1.5-T system. Instead, a multiple-animal acquisition methodology was demonstrated on a clinical 1.5-T scanner. This acquisition method significantly increases imaging efficiency and competes with single animal acquisitions at higher field.
Conclusion: Multiple-animal imaging using a standard clinical scanner has a great potential as a high-throughput acquisition method for small animals. 相似文献
5.
Riccardo Lencioni Ilario Menchi Alessandro Paolicchi Marco Carini Andrea Amorosi Carlo Bartolozzi 《Magma (New York, N.Y.)》1997,5(2):117-121
The purpose of this study was to determine whether endorectal coil magnetic resonance imaging (MRI) enables accurate assessment
of pathologic tumor volume in patients with clinically localized prostate carcinoma. Twenty-four patients with biopsy-proved
prostate carcinoma underwent MRI at 0.5 T before radical prostatectomy. Tumor volumes were determined independently on axial
fast-spin-echo (SE) T2-weighted MR images and whole-mount pathology slides of the surgical specimens. At pathology, tumor volumes ranged from 0.17
to 9.42 cm3 (mean±SD, 3.11±2.99 cm3). A strong correlation (r=.944) was found between measurements of tumor volume based on MR images and pathological specimens. The error was less than
0.5 cm3 in 14 cases, in the range of 0.5–1 cm3 in 7 cases, and more than 1 cm3 in 3 cases. By using an MR tumor volume of 2 cm3 as cutoff value, extracapsular tumor spread could be predicted with a sensitivity of 81.2%, a specificity of 100%, and an
accuracy of 87.5%. Tumor volume determinations based on MR images seem to be accurate enough to be helpful in clinical decision-making. 相似文献
6.
High-speed switching of current in gradient coils within high magnetic field strength magnetic resonance imaging (MRI) scanners results in high acoustic sound pressure levels (SPL) in and around these machines. To characterize the vibration properties as well as the acoustic noise properties of the gradient coil, a finite-element (FE) model was developed using the dimensional design specifications of an available gradient-coil insert and the concentration of the copper windings in the coil. This FE model was then validated using experimentally collected vibration data. A computational acoustic noise model was then developed based on the validated FE model. The validation of the finite-element analysis results was done using experimental modal testing of the same gradient coil in a free-free state (no boundary constraints). Based on the validated FE model, boundary conditions (supports) were added to the model to simulate the operating condition when the gradient-coil insert is in place in an MRI machine. Vibration analysis results from the FE model were again validated through experimental vibration testing with the gradient-coil insert installed in the MRI scanner and excited using swept sinusoidal time waveforms. The simulation results from the computational acoustic noise model were also validated through experimental noise measurement from the gradient-coil insert in the MRI scanner using swept sinusoidal time waveform inputs. Comparisons show that the FE model predicts the vibration properties and the computational acoustic noise model predicts the noise characteristic properties extremely accurately. 相似文献
7.
Chris K. Mechefske Ryan Geris Joseph S. Gati Brian K. Rutt 《Magma (New York, N.Y.)》2001,13(3):172-176
High-field, high-speed magnetic resonance imaging (MRI) can generate high levels of noise. There is ongoing concern in the
medical and imaging research communities regarding the detrimental effects of high acoustic levels on auditory function, patient
anxiety, verbal communication between patients and health care workers and ultimately MR image quality. In order to effectively
suppress the noise levels inside MRI scanners, the sound field needs to be accurately measured and characterized. This paper
presents the results of measurements of the sound radiation from a gradient coil cylinder within a 4 T MRI scanner under a
variety of conditions. These measurement results show: (1) that noise levels can be significantly reduced through the use
of an appropriately designed passive acoustic liner; and (2) the true noise levels that are experienced by patients during
echo planar imaging. 相似文献
8.
Heverhagen JT Ishaque N Zielke A Bohrer T Sitter H Berthold LD Klose KJ 《Magma (New York, N.Y.)》2001,12(1):4-9
Purpose: The purpose of this study was to evaluate MRI as a diagnostic tool in patients with suspected acute sigmoid diverticulitis.
Furthermore, we sought to develop an optimal imaging protocol in these patients.Patients and methods: Eleven patients with suspected acute diverticulitis were included in the study. All patients were imaged in a 1.0 T clinical
scanner using a body-array coil. Imaging sequences were single-shot TSE, HASTE-, STIR- and TrueFisp-sequence. All were obtained
in the frontal plane. The diagnosis was verified by a single experienced investigator, using ultrasound, and overall clinicopathological
outcome.Results: MRI enabled visualization of signs of an acute diverticulitis in all patients. However, the diagnosis of acute diverticulitis
was obtained in 10 patients only. The mean imaging time was 17.5 ± 5.5 min. STIR- and TrueFisp-sequences alone displayed all
findings, e.g pericolonic exsudation, edema and segmental narrowing, whereas SSTSE and HASTE-sequences showed no additional
information. Therefore, it appeared that the imaging protocol could be restricted to STIR- and TrueFisp-sequences.Conclusion: MRI is feasible as a fast, accurate and investigator-independent diagnostic tool in patients with suspected acute diverticulitis.
To prove its value in comparison to computed tomography or ultrasound, further studies are needed. 相似文献
9.
Chen F Suzuki Y Nagai N Peeters R Sun X Coudyzer W Marchal G Ni Y 《Magma (New York, N.Y.)》2004,17(3-6):103-108
A stroke model in rats with photochemically induced thrombosis (PIT) of proximal cerebral middle artery (MCA) is introduced for magnetic resonance imaging (MRI) study. Thirty-seven rats subjected to surgical and optical procedures for inducing the PIT models were scanned using a 1.5-T scanner with T1-weighted imaging (T1WI), T2-weighted imaging (T2WI), diffusion-weighted imaging (DWI), and contrast-enhanced perfusion-weighted imaging (PWI) at 1 h and 24 h after MCA occlusion. The penumbra evolution and PWI-derived parameters including relative cerebral blood volume (rCBV) and relative cerebral blood flow (rCBF) were monitored; and the relative lesion size (RLS) was compared with the final RLS on the gold standard triphenyl tetrazolium chloride (TTC) staining at 24 h. The results showed that the focal cerebral ischemic lesions were detectable in all rats with different MR approaches. The lesion on PWI at 1 h and on all MR images at 24 h was matched well with that seen on TTC staining; the peri-infarct area decreased from 6.2 ± 7.2% of the brain volume at 1 h to 0.3 ± 5.6% at 24 h. Compared to that in the contralateral hemisphere, rCBV in ischemic region was 52.6 ± 21.4 and 40.0 ± 15.8% (p > 0.05), and rCBF was 64.6 ± 11.2 and 47.3 ± 11.1% (p < 0.05) at 1 h and 24 h respectively. The present PIT model in rats has been successfully adopted for MRI research, which might be feasible for certain stroke studies and should be beneficial for the evaluation on effects of potential diagnostic and therapeutic approaches. 相似文献
10.
Jürgen Mäurer Herman Requardt Bernhard Sander Friedrich D. Knollmann Arne-jörn Lemke Thomas J. Vogl Roland Felix 《Magma (New York, N.Y.)》1996,4(1):27-33
To investigate the application of a mini-coil surface system for high-resolution MRI, 60 volunteers were examined in a 1.5-T whole-body scanner. Two replaceable probe heads were available: a circular 2.5-cm coil and a quadratic 5-cm coil, both of which were placed directly on the skin. The skin layers, Achilles tendon and finger joints were examined with the 2.5-cm coil and a FOV of 25 × 25 mm2. A matrix of 256 × 256 pixels resulted in a pixel size of 0.098 × 0.098 mm2. For imaging of the carpal tunnel, the 5-cm coil was used in transverse orientation. The FOV was 50 × 50 mm2 so that a matrix of 256 × 256 pixels led to a pixel size of 0.195 × 0.195 mm2. The resulting spatial resolution permitted visualization of the epidermis, dermis and subcutis, resulting in clear definition of anatomical detail of the musculoskeletal system. MRI measurement of skin-layer thickness did not correlate with histometric data (p<0.05). This discrepancy was due in part to shrinkage of the tumor specimen on histologic preparation. Other causes include the motion artifacts and the limited accuracy of determining thickness on the MRI display unit. 相似文献
11.
Oxygen enhanced MR ventilation imaging of the lung 总被引:3,自引:0,他引:3
The current work is a continuation of a new MRI technique that was proposed for the non-invasive assessment of regional lung
ventilation using inhaled molecular oxygen as aT
1 contrast agent. Several improvements of this technique are described in this work. The signal-to-noise ratio in the ventilation-scan
images was optimized using a centrically reordered single-shot RARE sequence with a short effective echo time and short inter-echo
spacing. The contrast-to-noise ratio was improved using an optimized inversion delay time. The optimized MR-ventilation-scan
was successfully performed in healthy volunteers and in an animal model with airway obstruction. The experimental results
demonstrate the feasibility and clinical potential of the MR ventilation imaging technique for assessment of regional pulmonary
function. 相似文献
12.
Franck Girard Tetsuya Suhara Takeshi Sassa Yoshiro Okubo Takayuki Obata Hiroo Ikehira Yasuhiko Sudo Masahisa Koga Hiroshi Yoshioka Katsuya Yoshida 《Magma (New York, N.Y.)》2001,13(1):1-7
Lithium salts have been widely used in the treatment of mood disorders, but the mechanism of action is still not clear. In
this work, a methodology for two-dimensional Lithium-7 imaging on clinical systems is presented. The data were acquired using
a phosphorus volume head coil that was re-tuned for the Lithium-7 frequency. A spectroscopic sequence was used to acquire
the free induction decay (FID) after volume excitation using a hard pulse. The results obtained on the head of patients undergoing
lithium treatment (n = 7, 0.6 mEq/1 average serum level) demonstrate that images of adequate signal to noise ratio (100:1) can be obtained in
acceptable imaging times (55 min) using the proposed methodology. The distribution of ’’Li appears uniform in the brains of
the patients studied. 相似文献
13.
Pilleul F Beuf O Godefroy C Scoazec JY Armenean M Armenean C Perrin E Valette PJ Jalmes HS 《Magma (New York, N.Y.)》2005,18(5):238-244
Purpose: This study assessed the value of high-resolution magnetic resonance imaging (MRI) of the distal colon by means of a dedicated
endoluminal magnetic resonance receiver coil on a 1.5-T clinical scanner.
Materials and Methods: To this end, single-loop, receive-only radio-frequency coils, housed in 18 F sheaths, were built. A 1.5-T clinical imager
was used. A 18 French diameter internal MRI receiver coil was inserted into the distal colon in 15 New Zealand rabbits to
obtain high-resolution magnetic resonance images by using T1-weighted Flash sequences with and without Fat Saturation (FS),
T2-weighted True-Fisp, turbo spin-echo, and T1-weighted Flash FS after contrast media injection. Images were compared to histological
sections.
Results: An adequate image quality was obtained in all specimens without significant artefacts. Based on histological reports, a five-layer
structure of the wall was considered normal. On different MR sequences, only two layers were identified on the images of all
rabbits specimens. The nearest layer to the mucosal surface was usually seen as a hyper intense layer and likely corresponds
to the mucosa. The highest difference of signal value between internal and external layers was performed on 2D Fat saturation
T1 weighted gradient echo. Comparison of mean signal value between the internal and external layers was statistically different
in for each sequence used in our protocol (P< 0.05).
Conclusion: Dedicated endoluminal RF coil provides good spatial resolution at the region of interest. On this prospective study of in
vivo rabbit, evaluation of colon walls allowed to provide detailed information. 相似文献
14.
Effects of restricted diffusion in a biological phantom: a q-space diffusion MRI study of asparagus stems at a 3T clinical scanner 总被引:1,自引:1,他引:0
Lätt J Nilsson M Rydhög A Wirestam R Ståhlberg F Brockstedt S 《Magma (New York, N.Y.)》2007,20(4):213-222
Introduction The aim of this work was to study the effects of restricted diffusion in a biological phantom consisting of green asparagus
stems using q-space MRI at a clinical scanner.
Method Measurements of the full width at half maximum (FWHM) of the displacement distribution were performed with varied diffusion
time (T
d). The accuracy of the measurements was investigated with respect to the degree of violation of the short gradient pulse (SGP)
condition, partial volume effects and a FWHM-based tensor model.
Results The measurements showed a reasonably constant FWHM perpendicular to the capillaries in the vascular bundles and an increased
FWHM parallel with the bundles when the T
d was increased. A 15% decrease in FWHM perpendicular to the bundles was observed when the diffusion encoding duration was
prolonged from 24 to 74 ms, owing to the violation of the SGP condition. For a population of different confinement sizes,
simulations indicated that the FWHM reflects the smaller sizes rather then the mean size of the confinements.
Conclusion A new method allowing tensor analysis of FWHM was derived and yielded accurate results. In conclusion, we found it possible
to measure the effects of restricted diffusion with q-space MRI using a clinical MRI scanner. 相似文献
15.
Object
The acoustic noise in a magnetic resonance imaging (MRI) scanner bore is mainly introduced by the vibration of gradient coils. The interaction between acoustic modes in the scanner bore and structure modes in the coil structure leads to structural–acoustic coupling. In order to implement quiet MRI design, the structural–acoustic coupling mechanism in MRI machines needs to be fully investigated. 相似文献16.
Gordon DeMeester Michael Morich Alex Byrne Frank Davies David Melotte Adrian Thomas 《Magma (New York, N.Y.)》2001,13(3):193-198
The desire to improve patient comfort and acceptance of high field magnetic resonance imaging (MRI) systems results in new-approaches
to magnet and other critical MRI component design. One such approach, based upon an anatomical field of view analysis, is
presented in this paper. The approach is utilized to define imaging volume requirements for short, high field, solenoid magnet
designs that maintain whole body imaging capability. A short magnet design with excellent magnetic field homogeneity is presented
accordingly. Combined with a novel flared gradient coil the overall system achieves improvements in openness. 相似文献
17.
Daniel K. Sodickson Charles A. McKenzie Michael A. Ohliger Ernest N. Yeh Mark D. Price 《Magma (New York, N.Y.)》2001,13(3):158-163
Parallel magnetic resonance imaging (MRI) techniques use spatial information from arrays of radiofrequency (RF) detector coils
to accelerate imaging. A number of parallel MRI techniques have been described in recent years, and numerous clinical applications
are currently being explored. The advent of practical parallel imaging presents various challenges for image reconstruction
and RF system design. Recent advances in tailored SiMultaneous Acquisition of Spatial Harmonics (SMASH) image reconstructions
are summarized. These advances enable robust SMASH imaging in arbitrary image planes with a wide range of coil array geometries.
A generalized formalism is described which may be used to understand the relations between SMASH and SENSE, to derive typical
implementations of each as special cases, and to form hybrid techniques combining some of the advantages of both. Accurate
knowledge of coil sensitivities is crucial for parallel MRI, and errors in calibration represent one of the most common and
the most pernicious sources of error in parallel image reconstructions. As one example, motion of the patient and or the coil
array between the sensitivity reference scan and the accelerated acquisition can lead to calibration errors and reconstruction
artifacts. Self-calibrating parallel MRI approaches that address this problem by eliminating the need for external sensitivity
references are reviewed. The ultimate achievable signal-to-noise ratio (SNR) for parallel MRI studies is closely tied to the
geometry and sensitivity patterns of the coil arrays used for spatial encoding. Several parallel imaging array designs that
depart from the traditional model of overlapped adjacent loop elements are described.
Summary of material presented at the 2001 ISMRM workshop on MRI hardware, Cleveland, OH, USA. 相似文献
18.
19.
The Transmission-Line Modelling (TLM) method is applied to the electromagnetic characterisation of RF coils and samples for
magnetic resonance imaging ()MRI. Theoretical verification was performed using a simple surface coil. Experimental verification
was performed using Alderman-Grant and birdcage coils constructed for use on a 7 T micro-imaging system. The modelling method
enabled electromagnetic characteristics of frequency response, electromagnetic field generation, energy stored and power loss
to be determined. From these parameters, coil resonant modes.B
1 field profiles, voltages, currents, quality factor (Q),π/2 pulse length, and the equivalent lumped-element circuit components of resistance, inductance and capacitance were calculated.
Equations are presented that enable a comprehensive electromagnetic characterisation of the RF coil and sample to be achieved
based on the results of the TLM simulations. The use of the TLM method is extended to include the design of safe arbitrary
multi-nuclear pulse sequences such that the specific absorption rate (SAR) of tissue, and RF coil component safety limits
are not exceeded. 相似文献
20.