Practical zero-shift tuning in geonium

Compositeness of the electron may show up in a very small deviation of the measured electron g factor from one calculated for a point electron by quantum electrodynamics. The precision of our g measurements is currently limited by an interaction of the cyclotron motion with standing waves in the trap cavity containing the electron. The important element introduced here is the systematic exploration of the trap cavity modes and the electron's coupling to them by measuring the shifted electron g factor gc = gc(omega e) as a function of the cyclotron frequency omega e. By measuring gc values at five different omega e values and modeling the trap cavity by six lumped LC circuits, the L values for the four most important modes may be determined and finally the unshifted g value may be extracted. Auxiliary experiments are relied upon only for the L values of the two least critical cavity modes. By designing the trap as a high-Q microwave cavity, an electron cyclotron and anomaly resonance linewidth one or even two orders of magnitude narrower than in free space may be approached without introducing appreciable frequency shifts.     

Geonium "K" experiment using spin dependency of cyclotron frequency supports g data of earlier geonium "S" work

By substituting the relativistic spin state dependence of the cyclotron frequency for the continuous Stern-Gerlach effect and running the geonium atom as a microsynchrocyclotron accelerator we have detected spin flips of the individual trapped electron. In our initial efforts we have been able to obtain a simple symmetric spin resonance about 4-fold narrower instead of a complex asymmetric one and also to support but not as yet seriously test the result of the earlier geonium "S" work, g/2 = 1. 001 159 652 185 5(40).     

Zero-shift tuning in geonium by variation of trapped charge.

Measuring the g factor, or gyromagnetic ratio of an individual electron or positron permanently confined in ultrahigh vacuum at liquid helium temperature, provides one of the few avenues for testing the currently accepted standard model that views these elementary particles, on the same level as the quarks, as point-like objects without internal structure. Our results, even though their error limits are the smallest ever attained, would still benefit by possibly two orders of magnitude if a shift, estimated at 4 parts in 10(12), caused by interaction of the cyclotron motion with standing electromagnetic waves in the trap cavity confining the electron could be eliminated. Reexamination of experimental data obtained in another connection suggests that it is practical to identify certain critical cyclotron frequency values for that the shift disappears by testing if the cyclotron frequency measured on a cloud of electrons does not vary with the number of electrons it contains. Clouds here must be kept very much smaller than the wavelength of the above standing waves.     

Nuclear magnetic resonance in gastroenterology

Insufficient clinical results are yet available to determine the likely clinical role of NMR in gastroenterology. In some instances unique information is available from NMR imaging but ultrasound and CT also provide valuable information in a wide variety of diseases. Many of the organs and tissues within the abdomen are accessible to biopsy, and a variety of other biochemical tests have specific roles in assessing disease within the abdomen and pelvis. Virtually all NMR machines in current use are research prototypes rather than clinical instruments designed for routine use. Major questions about design are unresolved, such as whether resistive, permanent or cryogenic magnets should be used. There is also little agreement about the optimum field for imaging. The value of spectroscopy in research and clinical use is another unknown factor and it is probable that this will provide useful information in research applications at least. At the present time it is important to note the developments occurring in NMR imaging and the potential of this technique, although it is not yet possible to predict what value it may have in clinical practice. There are many current research developments, such as flow imaging and the imaging of 23Na which have been demonstrated in the laboratory but have not yet been applied in clinical practice. It is also possible that respiratory gating may result in considerable improvement in image quality. The use of paramagnetic contrast agents is another developing field. These agents, including molecular O2, iron, manganese and gadolinium, have the effect of decreasing T1 and T2. Gadolinium chelates have been used in animals and will soon be evaluated in humans. Not only do these materials act as contrast agents in their own right but they may be linked as markers to metabolites, antibodies and other compounds. Direct measurements of T1 and T2 may prove to be of value although initial results indicate that they are rather non-specific. Whether NMR will remain largely of research interest or will play a useful role in clinical practice remains to be seen but will certainly be the subject of intense investigation over the next few years.     

Modeling left atrial volume,shape, and contraction patterns in normal subjects by cardiac magnetic resonance imaging

Background

Left atrial three-dimensional shape and contraction patterns are not well described. We quantified the LA using three-dimensional cardiac MRI (CMR) in a group of normal subjects.

Methods

Three-dimensional vectors were used to quantitate atrial shape and contraction using a geometric model as a three-dimensional prolate ellipsoid. Atrial area and length at end-systole and end-diastole were made in the horizontal long axis (HLA) and vertical long axis (VLA) planes. Biplane area–length products and the orthogonal LA long axis vector comprised 3 orthogonal vector lengths composed of axis measures for shape and volume calculations at end-diastole and end-systole. Vector fractional shortening in 3 dimensions was calculated for each 3-space orthogonal vector. Echocardiograms were used for comparison.

Results

The normal LA is an oblate ellipsoid with significantly longer HLA short axis than the vertical VLA short axis (p < 0.001). LA contraction in the long axis dimension is smaller than both HLA and VLA short axis dimensional changes (p < 0.001). Linear correlations between LAEDV vs. LASV and LAESV vs. LAEF were highly significant.

Conclusions

This dimensional analysis quantitates normal left atrial shape for the first time, modeled as a prolate 3-D ellipsoid. LA contractile functions and derives mostly from contraction in the HLA and VLA short axis directions. Though LA end-diastolic volume is considered the marker of left atrial health or disease, this notion should be reconsidered in view of LA static and functional modeling in 3 dimensions.     

Regional differences in shape and load in normal and diseased hearts studied by three dimensional tagged magnetic resonance imaging

Objectives: We aimed to characterize regional geometry in relation to load in two groups of patients with hypertrophic cardiomyopathy (HCM) and right ventricular pressure overload (RVPO) in relation to a group of subjects with normal left ventricular (LV) function. Background: Both these diseases are associated with marked changes in LV shape and function, which have not been studied with detailed three dimensional tools. Methods: Three dimensional (3D) tagged magnetic resonance imaging (MRI) was used to characterize the 3D geometry and regional stresses of the left ventricles in patients with HCM and RVPO. Curvatures, stresses, wall thickness, and endocardial motion were calculated from surface and volume elements. Results: Hearts with RVPO exhibited more circumferential and meridional flattening of the septum than normal and HCM hearts. The stress indices were lowest in the HCM hearts, compared to normal and RVPO hearts, due to the larger thicknesses. There was a more significant difference between lateral wall motion and other regional wall motions in the HCM and RVPO hearts as compared to normal hearts. Conclusions: It is suggested that curvature and stress mapping by 3D tagged MRI can be used as an important clinical tool for characterizing and distinguishing between healthy and diseased hearts. The results provided here validated previous knowledge on HCM and RVPO known from planary imaging methods.     

Breathhold unenhanced and gadolinium-enhanced magnetic resonance tomography and magnetic resonance cholangiography in hilar cholangiocarcinoma

We assessed the imaging characteristics of hilar cholangiocarcinoma in magnetic resonance imaging (MRI) and magnetic resonance cholangiography (MRC). Breathhold MRI (T2-weighted turbo spin echo sequences, unenhanced T1-weighted gradient echo sequences, and gadolinium-enhanced fat-suppressed gradient echo sequences) and breathhold MRC (fat-suppressed two-dimensional projection images) performed in 12 patients with histologically confirmed hilar cholangiocarcinoma were retrospectively reviewed for morphological tumor characteristics and contrast enhancement patterns. MRC demonstrated a significant bile duct stenosis with intrahepatic bile duct dilatation in all cases except in one patient who received an endoprothesis prior to imaging. Hilar cholangiocarcinoma was diagnosed by MRC only in one patient and MRI and MRC in 11. Mass lesions were seen in nine patients and circumferential tumor growth in three, including the patient diagnosed by MRC only. The tumor appeared hypointense relative to liver parenchyma in 10 of 11 patients in unenhanced T1-weighted images. T2-weighted sequences showed isointense or only slightly hyperintense signal in 5 of 11 patients, 3 of whom demonstrated desmoplastic reactions by histology. The other 6 patients revealed strongly hyperintense signal intensities. Contrast enhancement was increased compared to liver in 5 of 11 patients and decreased in 6 of 11 patients. MRI with MRC seem to be a sensitive tools in the detection of hilar cholangiocarcinomas. The variable imaging characteristics are most probably related to the inhomogeneous histological appearance of this tumor entity.     

Determination of the spatial orientation and shape of pulmonary vein ostia by contrast-enhanced magnetic resonance angiography.

AIMS: For catheter ablation of atrial fibrillation (AF), proper catheter positioning is crucial and depends on knowledge of pulmonary vein (PV) anatomy. The aim of this study was to assess PV spatial orientation and ostial shape by contrast-enhanced magnetic resonance angiography (CE-MRA). METHODS AND RESULTS: In 30 consecutive AF patients, CE-MRA was performed prior to ostial ablation. Using a centre-line technique, the PV ostium was defined perpendicular to this centre-line. Minimal and maximal ostial diameters, ostial perimeter, and angles in the anatomical frontal and transverse planes were measured. Twenty-one patients had four separate PVs. In four patients, there was a distinct right-middle PV and in five a common left common PV was found. Left-sided PV ostia were smaller and more elliptical than right-sided PVs. In the transverse plane, the ostia of both superior PVs were directed anteriorly (LS -15 +/- 13 degrees , RS -13 +/- 11 degrees ) and both inferior PV ostia were directed posteriorly (LI 23 +/- 15 degrees , RI 39 +/- 15 degrees ). In the frontal plane, both superior PV ostia pointed upwards (LS -27 +/- 14 degrees , RS -33 +/- 12 degrees ) while the inferior ostia were directed horizontally (LI 2 +/- 11 degrees , RI 3 +/- 13 degrees ). CONCLUSION: PV ostial shape and spatial orientation are variable and can be visualized adequately by CE-MRA.     

Thoracic magnetic resonance imaging

In our experience, MR has served largely as a problem-solving device, especially in those cases in which CT has proved equivocal. Magnetic resonance has been especially efficacious in evaluating cardiovascular pathology. Virtually the entire spectrum of aortic disease can be assessed accurately, making MR a reasonable alternative to CT or angiography in most cases. Indications for the use of MR in patients with thoracic neoplasia have also emerged. Magnetic resonance is more accurate than CT in assessing invasion of the chest wall and mediastinum. As a consequence, MR should be considered the imaging procedure of choice in patients with suspected Pancoast tumors. In some patients with lymphoma, MR can make a unique contribution by evaluating the response to therapy. Magnetic resonance also can be of value in assessing patients with signs of venous obstruction, especially when there is a contraindication to the use of intravenous contrast medium. Magnetic resonance is as accurate as CT in assessing most benign mediastinal pathology. The former study can easily differentiate atherosclerotic vessels or aneurysms from enlarged lymph nodes or masses, frequently obviating a more invasive study. It is especially efficacious in evaluating patients with cystic lesions, especially those with complex cysts not clearly of water density. In the hilum, MR can differentiate prominent hilar vessels from adenopathy or masses as reliably as CT. Again, in patients with renal failure or those who have documented allergies to iodinated contrast medium, MR should be the imaging procedure of choice to evaluate suspicious hila identified on plain chest radiographs. Magnetic resonance also can be used to differentiate central obstructing hilar tumors from peripheral collapsed lung. In certain cases, these findings may help determine resectability by demonstrating encasement of hilar and mediastinal vessels as well as the central airways. It should be anticipated that as technologic improvements continue to be made, MR will assume an increasingly important role in the imaging of thoracic disease.     

Cardiac magnetic resonance spectroscopy

This review describes recent advances in cardiac magnetic resonance spectroscopy (MRS). MRS allows noninvasive characterization of the metabolic state of cardiac muscle, in both animal and human models. Recent experimental MRS studies have allowed new insights into the essential role of energetics in heart failure. Various new studies suggest a rapidly growing role of MRS for phenotyping new genetically modified mouse models, and recent methodologic advances include development of absolute quantification of high-energy phosphates, measurement of ATP turnover rates and thermodynamic parameters (such as free ADP and free energy change of ATP hydrolysis), and improved acquisition sequences. New patient studies demonstrate the potential value of MRS as a clinical diagnostic tool in patients with ischemic heart disease, heart failure, cardiac transplantation, valve disease, and genetic cardiomyopathy.     

Coronary magnetic resonance imaging

This article highlights the technical challenges and general imaging strategies for coronary MRI. This is followed by a review of the clinical results for the assessment of anomalous CAD, coronary artery aneurysms, native vessel integrity, and coronary artery bypass graft disease using the more commonly applied MRI methods. It concludes with a brief discussion of the advantages/disadvantages and clinical results comparing coronary MRI with multidetector CT (MDCT) coronary angiography.     

Nuclear magnetic resonance imaging

Conclusion As compared to other techniques MRI offers many advantages. It enables one to differentiate the nucleus pulposus within the disc and reveals the discal degeneration. It reveals more precisely the relationships with nervous formations and it is invaluable for the detection and exploration of bone tumors and metastasis, of deformations, of the cervico-occipital junction, of the cervical and dorsal medullar lesions and of infectious processes. As for peripheral joints, it seems to be useful in the study of deposits, infections of bones or joints, osteonecrosis, algodystrophy. It also proves useful in the exploration of the synovialis of inflammatory rheumatism, of metabolic arthropathy, of lesions in the tendons, muscles, menisci or ligaments. It is not quite as interesting for arthritis and chondrocalcinosis but further developments may alter this situation.     

Coronary magnetic resonance angiography

Despite advances in both prevention and treatment, cardiovascular disease remains the leading cause of morbidity and mortality in the United States. The current gold standard for the diagnosis of coronary artery disease is the x-ray coronary angiogram, which is both costly and associated with a small risk of morbidity. More than 1 million Americans are referred for this test annually, and despite the availability of numerous noninvasive tests to identify patients with coronary artery disease, > or =35% of patients referred for this test are found not to have disease. It therefore would be beneficial to use a noninvasive test to allow the presence of coronary atherosclerosis to be determined directly. Coronary magnetic resonance angiography, a technique that is aimed at establishing a noninvasive test for the assessment of significant coronary stenoses, obviates the risks of patient exposure to radiation of x-ray angiography and therefore represents a major step forward in diagnostic cardiology.     

Virtual magnetic resonance colonography

Colorectal cancer screening has vast potential. Beyond considerations for cost and diagnostic accuracy, the effectiveness of any colorectal screening strategy will be dependent on the degree of patient acceptance. Magnetic resonance (MR) colonography has been shown to be accurate regarding the detection of clinically relevant colonic polyps exceeding 10 mm in size, with reported sensitivity and specificity values exceeding 95%. To further increase patient acceptance, strategies for fecal tagging have recently been developed. By modulating the signal of fecal material to be identical to the signal characteristics of the enema applied to distend the colon, fecal tagging in conjunction with MR colonography obviates the need for bowel cleansing. The review will describe the techniques underlying MR colonography and describe early clinical experience with fecal tagging techniques.     

Cardiovascular magnetic resonance imaging

Recent advancements in magnetic resonance imaging hardware and software permit the assessment of cardiovascular structure and function at rest and during exercise or pharmacology-induced cardiac stress. With these developments, knowledge of cardiovascular imaging protocols in the magnetic resonance imaging environment is critical for nursing personnel. The purpose of this article is to review information pertinent to working in a magnetic resonance imaging environment and to describe the requirements of nursing personnel performing cardiovascular magnetic resonance imaging examinations.