Simple correction method for k-space trajectory deviations in MRI

STUDY OBJECTIVES: Recently, pulmonologists have performed thoracoscopy under local anesthesia using rigid thoracoscopes or flexible bronchoscopes. The latter allow greater access within the pleural cavity but are difficult to manipulate. The Olympus LTF semiflexible fiberoptic thoracoscope combines features of both instruments, having a solid body and a flexible terminal section. In the first study with this instrument, we evaluated ease of use and compared diagnostic yield with closed needle biopsy. PATIENTS: Twenty-four patients with pleural effusion were investigated. SETTING: Scottish University Hospital. DESIGN: Thoracoscopy was performed in the bronchoscopy suite after premedication with atropine and papaveretum. Following a standard Abram's needle biopsy, the LTF thoracoscope was inserted through a flexible introducer (Olympus Optical Co Ltd; Tokyo, Japan). The pleura was inspected and biopsy specimens were taken of suspicious areas. RESULTS: The final diagnosis was malignant pleural effusion in 16 of 24 patients. Ten of 16 were positive by Abram's biopsy, giving a sensitivity of 62%. Thirteen of 16 were positive by fiberoptic thoracoscopy, giving an improved sensitivity of 81%. The LTF thoracoscope was easy to use for pulmonologists experienced in rigid thoracoscopy and flexible bronchoscopy. Excellent views of the pleura were obtained from a single entry point. The procedure was well tolerated and no complications were encountered. CONCLUSION: The LTF thoracoscope allows excellent pleural access but a larger biopsy channel (currently 2 mm) might increase the accuracy of diagnosis.     

A rapid 2D time-resolved variable-rate k-space sampling MR technique for passive catheter tracking during endovascular procedures

The protease-activated receptor-2 (PAR-2) is a seven transmembrane domain receptor related to the thrombin receptor, which is activated in vitro by cleavage by trypsin. Affinity-purified rabbit IgG raised against a peptide corresponding to the trypsin cleavage site of PAR-2 was used for an immunohistochemical study of skin. The expression of PAR-2 in epidermis was striking, with keratinocytes showing abundant intercellular and cytoplasmic staining. Basal cells showed the strongest staining intensity and the stratum corneum was negative. Staining with control IgG used at the same concentration was consistently negative. The functional expression of PAR-2 by the simian virus transformed human skin keratinocyte cell line SVK14 was demonstrated by Northern blot analysis, flow cytometric analysis and the measurement of intracellular calcium. Treatment of SVK14 with trypsin or a receptor agonist peptide (SLIGKV-NH2) caused a dose-dependent increase in the secretion of the chemokine interleukin-8 (IL-8) in vitro. The effect of the peptide was specific, since control acetylated peptide was without activity. We conclude that PAR-2 is highly expressed by epidermal keratinocytes and receptor activation in vitro leads to increased IL-8 secretion by keratinocytes. These data raise the possibility that PAR-2 may play a role in epidermal homeostasis and inflammatory conditions.     

A new technique for continuous sphincter pressure measurement

A cannula and conveniently arranged ancillary apparatus designed to assist endotracheal intubation of patients with upper respiratory tract obstruction prior to tracheostomy are described.     

A novel technique for containerless protein crystallization

Heterogeneous nucleation, which is often detrimental to the production of suitable crystals for X-ray diffraction, can be induced by the contact of a crystallization sample with the walls of its supporting vessel. A novel method for creating a 'containerless' environment for the growth of protein crystals is described. Contact between the container walls and a crystallization drop is eliminated by suspending the drop between two oils of different density: one of higher and the other of lower density than that of water and the common precipitating agents. A number of proteins were crystallized in 2-10 microliters drops using this procedure. It was found that the number of crystals obtained in such suspended drops was reduced significantly compared with the number of crystals obtained in trials where the crystallization drop was situated at the bottom of a vial under a single layer of oil. This method has potential in controlling heterogeneous nucleation.     

In vitro validation of the luminal measurement of a novel catheter based moulding technique

OBJECTIVE: To investigate a modified angioplasty balloon catheter, which uses a novel balloon polymer to produce luminal moulds. DESIGN: The catheter was tested in polyurethane phantoms of diameter 1.5 to 4.0 mm. Inflations were to 1.4 atmospheres for 20 seconds at 37 degrees C. The moulds were viewed by reinflating the balloon to 0. 34 atmospheres and quantified using macrophotography and caliper measurement. RESULTS: Evidence of systematic error was found with lumen diameters 相似文献   

A technique for measurement of methylmalonic acid in cattle urine

Methylmalonic acid was measured in cattle urine by decarboxylating it to propionate with sulfuric acid and heat and quantifying the propionate so formed by gas-liquid chromatography. Crystalline methylmalonic acid added to cow urine was recovered quantitatively.     

A proposed technique for intraoperative measurement of cervical spine stiffness

Research reported here addresses the issue of the reliability of retrospective reports of children's perceptions of maternal acceptance-rejection as measured by the Parental Acceptance-Rejection Questionnaire. A sample of 49 middle-class Caucasian 7- to 11-yr.-old children were asked to respond to the questionnaire reflecting on their mothers' current accepting-rejecting behaviors. Seven years later the same children--now adolescents--responded to the same questionnaire with the instruction to reflect back on their mothers' behavior when the youth were about 7 to 11 years of age. None of these youth recalled having been tested seven years earlier. A simple zero-order correlation between scores in childhood and adolescence was 62, indicating that adolescents' retrospective recollections were in moderate agreement with their reports during childhood. Thus, it seems clear that, at least with respect to perceptions of maternal acceptance-rejection as measured by the Parental Acceptance-Rejection Questionnaire, researchers can have reasonable confidence that adolescents' current recollections about their experiences of maternal acceptance-rejection are likely to be in moderate agreement with what they would have reported had they been tested during childhood.     

Lumbar lordosis measurement. A new method versus Cobb technique

STUDY DESIGN: A historic cross-sectional study of lumbar lordosis in 199 healthy individuals aged 1-30 years. OBJECTIVE: To evaluate the magnitude and rate of the development of the normal lumbar lordotic curve with age using two methods of measurement. SUMMARY OF BACKGROUND DATA: There is no agreement among spine physicians on the range of the normal lumbar lordotic curve. In certain conditions, such as a tethered spinal cord, a change in lordotic curve may indicate or even precede the onset of neurologic symptoms. Reliable measurements of the lumbar lordotic curve may aid in the early diagnosis and management of these conditions, before irreversible neurologic change ensues. METHODS: The lumbar lordotic curve was measured by the traditional Cobb technique and by a newly designed method, tangential radiologic assessment of lumbar lordosis. The data were subjected to the Morgan-Pitman test for correlated variances to observe which of the two methods was more reliable in measuring the magnitude and rate of change in the lumbar lordotic curve. RESULTS AND CONCLUSIONS: The rate of development of the lumbar lordotic curve appears to be nonlinear, increases during first year of life and during puberty, and reaches a plateau of approximately 50 degrees at maturity. The tangential radiologic assessment of lumbar lordosis method is more reproducible and more reliable in the lumbar lordotic curve, providing a smaller range of normal values (8 degrees-16 degrees less) than the Cobb method.     

A method to measure arbitrary k-space trajectories for rapid MR imaging

We assessed the clinical usefulness of the intraductal secretin test in order to ascertain whether it can substitute for the conventional duodenal secretin test. Duodenal juice was obtained with a triple-lumen tube and pure pancreatic juice was obtained by retrograde cannulation of the main pancreatic duct using a duodenofiberscope. Pancreatic secretion was stimulated by a bolus intravenous injection of secretin (100 units). The two tests showed comparable interindividual coefficients of variation, significantly good correlations, and comparable diagnostic efficiencies. The intraductal secretin test showed no less reproducibility than that of the duodenal secretin test as reported in the literature. In the intraductal secretin test, secretory volume, peak flow rate, bicarbonate output, and lipase output yielded the best diagnostic efficiency, followed by amylase output and maximal bicarbonate concentration. In the intraductal secretin test, a 10-min collection provided as much information as a 20-min collection. We conclude, therefore, that the 10-min intraductal secretin test is as useful as the conventional duodenal secretin test in assessing exocrine pancreatic function and that the most discriminatory parameters are secretory volume, bicarbonate output, and amylase (or lipase) output.     

A novel approach to microcalcification detection using fuzzy logic technique

Breast cancer continues to be a significant public health problem in the United States. Approximately, 182,000 new cases of breast cancer are diagnosed and 46,000 women die of breast cancer each year. Even more disturbing is the fact that one out of eight women in the United States will develop breast cancer at some point during her lifetime. Since the cause of breast cancer remains unknown, primary prevention becomes impossible. Computer-aided mammography is an important and challenging task in automated diagnosis. It has great potential over traditional interpretation of film-screen mammography in terms of efficiency and accuracy. Microcalcifications are the earliest sign of breast carcinomas and their detection is one of the key issues for breast cancer control. In this study, a novel approach to microcalcification detection based on fuzzy logic technique is presented. Microcalcifications are first enhanced based on their brightness and nonuniformity. Then, the irrelevant breast structures are excluded by a curve detector. Finally, microcalcifications are located using an iterative threshold selection method. The shapes of microcalcifications are reconstructed and the isolated pixels are removed by employing the mathematical morphology technique. The essential idea of the proposed approach is to apply a fuzzified image of a mammogram to locate the suspicious regions and to interact the fuzzified image with the original image to preserve fidelity. The major advantage of the proposed method is its ability to detect microcalcifications even in very dense breast mammograms. A series of clinical mammograms are employed to test the proposed algorithm and the performance is evaluated by the free-response receiver operating characteristic curve. The experiments aptly show that the microcalcifications can be accurately detected even in very dense mammograms using the proposed approach.     

Polar sampling in k-space: reconstruction effects

Magnetic resonance images are most commonly computed by taking the inverse Fourier transform of the k-space data. This transformation can potentially create artifacts in the image, depending on the reconstruction algorithm used. For equally spaced radial and azimuthal k-space polar sampling, both gridding and convolution backprojection are applicable. However, these algorithms potentially can yield different resolution, signal-to-noise ratio, and aliasing characteristics in the reconstructed image. Here, these effects are analyzed and their tradeoffs are discussed. It is shown that, provided the modulation transfer function and the signal-to-noise ratio are considered together, these algorithms perform similarly. In contrast, their aliasing behavior is different, since their respective point spread functions (PSF) differ. In gridding, the PSF is composed of the mainlobe and ringlobes that lead to aliasing. Conversely, there are no ringlobes in the convolution backprojection PSF, thus radial aliasing effects are minimized. Also, a hybrid gridding and convolution backprojection reconstruction is presented for radially nonequidistant k-space polar sampling.     

Frequency response of multi-phase segmented k-space phase-contrast

A theoretical analysis of the temporal frequency response of multi-phase segmented k-space phase-contrast was developed. This includes the effects of both segment duration and the number of cardiac phases that are reconstructed. An increase in the number of views per segment and the corresponding increase in segment duration results in an increased smoothing or low-pass filtering of the time-resolved flow waveform. Reconstruction of all intermediate cardiac phases makes the Nyquist sampling frequency independent of the number of views per segment. This analysis was verified experimentally using a multi-phase phase-contrast segmented k-space MR pulse sequence. This sequence reconstructs all intermediate cardiac phases and uses fractional segments at the end of the cardiac cycle if an entire segment does not fit. The use of fractional segments increases the portion of the cardiac cycle over which data are acquired.     

Volumetric spectroscopic imaging with spiral-based k-space trajectories

Spiral-based k-space trajectories were applied in a spectroscopic imaging sequence with time-varying readout gradients to collect volumetric chemical shift information. In addition to spectroscopic imaging of low signal-to-noise ratio (SNR) brain metabolites, the spiral trajectories were used to rapidly collect reference signals from the high SNR water signal to automatically phase the spectra and to aid the reconstruction of metabolite maps. Spectral-spatial pulses were used for excitation and water suppression. The pulses were designed to achieve stable phase profiles in the presence of up to 20% variation in the radiofrequency field. A gridding algorithm was used to resample the data onto a rectilinear grid before fast Fourier transforms. This method was demonstrated by in vivo imaging of brain metabolites at 1.5 T with 10 slices of 18 x 18 pixels each. Nominal voxel size was 1.1 cc, spectral bandwidth was 400 Hz, scan time was 18 min for the metabolite scan and 3 min for the reference scan.