Correlation of C-myc and HER-2/neu amplification and expression with histopathologic variables in uterine corpus cancer

OBJECTIVE

Initial studies of protooncogenes in uterine corpus cancer have focused on a single aspect of the gene in question (deoxyribonucleic acid, ribonucleic acid, protein) or have studied a small number of patients. Therefore we evaluated c-myc and HER-2/neu gene amplification and ribonucleic acid overexpression in such malignancies and correlated these molecular changes with known pathologic risk factors.

STUDY DESIGN

Quantitative Southern blot analysis for oncogene deoxyribonucleic acid was used to examine 37 tumors from patients with primary untreated uterine corpus cancer referred to the City of Hope National Medical Center. Six normal endometrial specimens were controls. Seventeen tumors were also examined by Northern blotting to assess increased ribonucleic expression.

RESULTS

Histologic types included adenocarcinoma (n = 30), papillary serous adenocarcinoma (n = 2), adenosquamous carcinoma (n = 2), mixed mullerian sarcoma (n = 2), and leiomyosarcoma (n = 1). Carcinomas were stage I (n = 10), II (n = 18), or III (n = 6). Twenty-three had myometrial invasion of less than one third, six one third to two thirds, and eight deeper invasion (greater than two thirds). According to the criteria of the International Federation of Gynecology and Obstetrics stage was as follows: I (n = 22), II (n = 3), III (n = 7), and IV (n = 5). Ten (27%) and four (11%) tumors showed gene amplification of c-myc and HER-2/neu, respectively. Six demonstrated overexpression of either the c-myc or HER-2/neu gene. HER-2/neu gene amplification was associated more closely with overexpression. Stepwise logistic analysis demonstrated c-myc amplification to be associated with higher grade (p = 0.01).

CONCLUSION

In this referral population, c-myc activation is more common than HER-2/neu activation in uterine corpus cancer and is associated with tumors of higher grade.

Tensile and viscoelastic properties of human patellar tendon

The tensile and viscoelastic properties of fresh-frozen, nonirradiated human patellar tendon were investigated in two groups of 15 specimens: one group was from individuals 29-50 years old and the other group was from individuals 64-93 years old. The central portion of each patella-patellar tendon-tibia complex was subjected to cyclic preconditioning, stress-relaxation, cyclic stress-relaxation, and load to failure tests. For each age group, stress-relaxation and stress-strain curves were obtained, from which percentage relaxation, ultimate tensile strength, strain at failure, modulus, and strain energy density were determined. Viscoelastic behavior was described with use of quasilinear viscoelasticity. The younger group showed a 46 +/- 9% (mean +/- SD) decrease in stress after 15 minutes, whereas the older group exhibited a 50 +/- 6% decrease. The values for ultimate tensile strength and strain at failure, respectively, were 64.7 +/- 15.0 MPa and 14 +/- 6% for the younger group and 53.6 +/- 10.0 MPa and 15 +/- 5% for the older group. Modulus values were 660 +/- 266 MPa for the younger group and 504 +/- 222 MPa for the older group. Except for ultimate tensile strength, which was 17% less for the older group than for the younger one, no statistically significant differences were found in tensile or viscoelastic properties. This study indicated that there were minimal differences in biomechanical properties of the substance of the patellar tendon between younger and older age groups.

The architecture of plant vasculature and transport as seen with magnetic resonance microscopy

Water and photosynthate transport through plants has been studied extensively for the past three centuries. Few techniques are available that are capable of providing both physiological and anatomical information, and most are destructive in nature. We report the use of high resolution magnetic resonance microscopy (MRM) for the study of intact plant vasculature. Both two- (2-D) and three-dimensional (3-D) image acquisition protocols are employed wherein the plant vasculature can be readily distinguished from surrounding parenchymal tissue. In the 3-D image sets, the vasculature has been digitally segmented, allowing isolation of only the intact vascular architecture. The paths of water and photosynthate transport into several plant specimens have been visualized in this manner. Images of sugar beets, plants that store high concentrations of sucrose within the parenchyma, show contrast patterns between vasculature and parenchyma that are opposite to those seen in images acquired of an apple, fig, okra pod, kiwi fruit, and potato, plants that do not store high concentrations of sucrose. This suggests that transport and accumulation of photosynthates may be partially responsible for contrasts seen within images acquired of these plant specimens. Key words: transport, transpiration, sugar, MRI, magnetic resonance imaging, plants.

Immunization of mice against a synthetic N-terminal extracellular domain gonadotropin-releasing hormone receptor peptide: evidence for a direct uterine effect

PROBLEM

Immature male and female mice were immunized with a synthetic peptide corresponding to amino acids 5-17 (ASLEQDPNHCSAI) of the mouse hypophyseal gonadotropin-releasing hormone (GnRH) receptor.

METHOD

Effect of immunization (postpuberal) was restricted to the uterus. Pituitary-gonadal functions were not altered.

RESULTS

The endometrial lining of immunized females was thin and lacked glandular development. These observations were corroborated in actively immunized and passively immunized adult females.

CONCLUSIONS

Apparently endometrial cells express a unique surface antigen, though reactive with antipeptide antibodies, that differs from the prototype pituitary GnRH receptor. Antibodies that selectively inhibit endometrial maturation might be used to treat proliferative diseases of the uterus.

Magnetic resonance microscopy of the rat carotid artery at 300 megahertz

RATIONALE AND OBJECTIVES

Magnetic resonance microscopy (MRM) has evolved from a technical curiosity to a tool with which researchers can study important disease models. But MRM is not simply an extension of clinical magnetic resonance imaging. In this article, the unique adaptations of MRM required in the study of carotid artery disease are outlined. The techniques of MRM are integrated into a specific model of carotid artery disease in the rat to allow in vivo studies of vascular wall thickening after removal of the vascular endothelium.

METHODS

Imaging was performed at 300 MHz in 250-gm Sprague-Dawley rats using surgically implanted radiofrequency coils to localize the region of interest and to provide an increase in the signal-to-noise ratio over that of volume or surface coils. A three-dimensional Fourier encoding sequence was modified with flow-dephasing gradients to minimize signal and artifacts from moving blood.

RESULTS

In vivo images were acquired with spatial resolution of 25 x 25 x 400 microns and signal-to-noise ratio more than sufficient to define the morphology of the vascular wall. Significant changes in the intensity and distribution of signal were visible in the area surrounding the vessel after angioplasty.

CONCLUSIONS

Signal-to-noise improvements from surgically implanted coils coupled to a three-dimensional radiofrequency-refocused sequence with flow-dephasing gradients were sufficient to define the wall of the carotid artery. The diffusion-weighted pulse sequence detects signal changes in the area surrounding the vessel after angioplasty. The MRM techniques described and the contrast observed allow us, for the first time to follow in vivo the early stage of developing atherosclerosis in the vessel wall and closely surrounding tissue.

Three dimensional magnetic resonance microangiography of rat neurovasculature

Techniques are described to perform three dimensional (3D) MR microangiography. We have combined the use of a blood pool agent (Gd-DTPA-complexed with bovine serum albumin), three dimensional Fourier encoding, careful animal stabilization, and volume rendering to permit imaging with voxels of 60 x 60 x 60 microns. 3DFT encoding has been performed at 7.1 T with very large arrays (256 x 512 x 512). Interactive volume rendering allows a number of unique display opportunities that effectively exploit these isotropic 3D arrays.

Use of gamma-glutamyl transpeptidase activity as a marker of hair cycle and anagen induction in mouse hair follicles

gamma-glutamyl transpeptidase activity was monitored in cycling mice by histologic localization and biochemical assay. Our objective for this study is to establish the relationship between gamma-glutamyl transpeptidase activity and hair growth and to determine whether its activity can be correlated to induced hair growth. In cycling mouse skin, gamma-glutamyl transpeptidase activity is pronounced during anagen and greatly diminished during telogen. In the skin, the enzyme is present exclusively in the outer and inner root sheaths of hair follicles. gamma-glutamyl transpeptidase is limited to the follicle below the level of the sebaceous gland and is completely absent in the follicle above the sebaceous gland level. During anagen, the outer root sheath in the hypodermis is intensely positive for gamma-glutamyl transpeptidase activity whereas the hair matrix cells and dermal papillar are negative. The inner root sheath above the bulb shows distinctive membrane staining for gamma-glutamyl transpeptidase. gamma-glutamyl transpeptidase activity can be seen to vary only in cycling follicles. Inducing anagen by plucking hair shafts results in an increase in gamma-glutamyl transpeptidase activity directly correlated to hair regrowth. In a similar manner, mice were plucked and treated with a daily dose of 2% minoxidil. A slight difference in cycle lengths was seen in animals treated with minoxidil when compared to vehicle control. Minoxidil treatment may cause an early initiation of anagen, but both the minoxidil-treated skin and the vehicle-treated skin entered telogen at the same time. Together, these studies indicate that gamma-glutamyl transpeptidase is a specific marker of anagen in growing hair.

Induction of apoptotic or lytic death in an ovarian adenocarcinoma cell line by antibodies generated against a synthetic N-terminal extracellular domain gonadotropin-releasing hormone receptor peptide

A polyclonal antiserum was generated in ovariectomized sheep against a synthetic peptide corresponding to amino acids 5-17 of the deduced mouse pituitary gonadotropin-releasing hormone (GnRH) receptor. Antipeptide antibodies did not bind native cells, but did react strongly with a human ovarian cancer cell line (OVCAR-3) reportedly sensitive to GnRH. Growth of cultured OVCAR-3 cells was specifically suppressed by antipeptide serum. This was attributed in part to programmed death (chromatin condensation and DNA fragmentation) of cells by antibody-induced apoptosis. Antibodies also exhibited a cytolytic effect (lactate dehydrogenase release) toward OVCAR-3 cells in the presence of the complement. Endometria of passively immunized mice lacked development; thus, antipeptide antibodies evidently recognize Mullerian duct derivatives. Experiments are in progress to determine whether the putative antigen is a variant of the pituitary GnRH receptor or a largely dissimilar protein. Effector-functional antibodies could be useful in the management of ovarian or uterine neoplasia.

Studies on bromobenzene-induced hepatotoxicity using in vivo MR microscopy with surgically implanted RF coils

Using surgically implanted RF coils at 300 MHz, three-dimensional microscopic MR images of rat liver were obtained in vivo to follow the development of pathology induced by bromobenzene exposure. Formalin fixed specimens of liver from these animals were also imaged using in vitro MR microscopy, followed by conventional optical microscopy. All MR images were acquired using a spin-warp pulse sequence with TR = 950 ms and TE = 23 ms. The in vivo images were reconstructed as 256(2) x 32 arrays with a voxel size of (50 microns)2 x 219 microns, while the in vitro images were reconstructed as 256(2) x 128 arrays, giving an isotropic resolution at (39 microns)3. Based on results from six animals, we have found in all animals exposed to bromobenzene, image intensity decreased in specific hepatic tissue regions. These regions were well correlated to low signal intensity areas observed in in vitro MR images at higher resolution. Conventional optical microscopy indicated that the low signal intensity regions corresponded to areas of necrosis. The decrease in signal intensity is consistent with increased local diffusion coefficients as a result of necrosis. This study demonstrates that MR microscopy with implanted RF coils can be successfully used to follow tissue pathological changes in living tissues.

Magnetic resonance imaging of chronic myocardial infarcts in formalin-fixed human autopsy hearts

BACKGROUND

In post-myocardial infarction patients, three-dimensional structure of the infarct as well as infarct size are likely to be important factors affecting mortality, cardiac function, and arrhythmias. Current morphological methods for determining three-dimensional infarct structure in autopsied hearts are inexact and time consuming. The cardiac magnetic resonance imaging techniques used in living patients have shown potential in determining infarct size and structure but have limited resolution for morphometric postmortem studies. The recent development of magnetic resonance microscopy raises the possibility that three-dimensional infarct structure can be quantified at microscopic levels in autopsied hearts. The purpose of this study was to determine the ability of magnetic resonance imaging at different spatial resolutions to differentiate infarcted from noninfarcted myocardium.

METHODS AND RESULTS

Magnetic resonance imaging was performed at 2.0 T on cross sections taken from 10 autopsied hearts containing old myocardial infarcts. T1 was derived from six images with repetition times (TRs) for each image ranging from 100 to 3200 milliseconds. T2 was derived from multi-echo images with echo times (TEs) ranging from 10 to 60 milliseconds. Resolution was approximately 400 x 400 microns in 2-mm-thick slices. Sites of infarcted and noninfarcted tissue were identified from histological sections taken from each slice, and the T1 and T2 values of these sites were obtained. Microscopic images were acquired with voxels of 100 x 100 x 625 microns, representing tissue volumes more than 1000-fold smaller than conventional clinical images. In all cases, T1 of infarcted tissue (459 +/- 266 milliseconds, mean +/- SD) was greater than that of noninfarcted tissue (272 +/- 163 milliseconds). Also, in all cases, T2 of infarcted tissue (49 +/- 14 milliseconds) was greater than that of noninfarcted tissue (35 +/- 8 milliseconds).

CONCLUSIONS

T1 and T2 values for infarcted tissue are significantly different from those of noninfarcted tissue (P < .001). Based on these findings, it should be possible to develop techniques to perform three-dimensional imaging and quantitation of infarcts with a resolution of 400 microns or less. When volumetric three-dimensional imaging was performed using a T1-weighted sequence, the resulting 256(3) arrays supported isotropic resolution at 400 microns (voxel volume, 0.064 mm3). Subsequent volume rendering using a compositing algorithm clearly shows the infarcted areas in three dimensions. The techniques demonstrate the potential for quantitative three-dimensional cardiac morphometry using magnetic resonance imaging.

Imaging the cochlea by magnetic resonance microscopy

The isolated, fixed cochlea of the mustached bat was studied with three dimensional magnetic resonance (MR) microscopy. The cochlea of this animal is about 4 mm in diameter and its entire volume was imaged. With the field of view and matrix size used, the volume elements (voxels) making up the volume data set were isotropic 25 x 25 x 25 micron cubes. Three dimensional (3D) MR microscopy based on isotropic voxels has many advantages over commonly used light microscopy: 1) it is non destructive; 2) it is much less time consuming; 3) no dehydration is required and shrinkage is minimized; 4) the data set can be used to create sections in any desired plane; 5) the proper alignment of sections is inherent in the 3D acquisition so that no reference points are required; 6) the entire data set can be viewed from any point of view in a volume rendered image; 7) the data is digital and features can be enhanced by computer image processing; and 8) the isotropic dimensions of the voxels make the data well-suited for structural reconstructions and measurements. Good images of the osseous spiral lamina, spiral ligament, scala tympani, scala vestibuli, and nerve bundles were obtained. The vestibular (Reissner's) membrane was easily identified in the mustached bat and it appears to bulge into the scala vestibuli. The visibility of this structure suggests that MR microscopy would be well-suited for studies of endolymphatic hydrops.

Magnetic resonance microscopy of mouse embryos

The increased use of the mouse as a model for various aspects of mammalian biology has caused a renewed interest in developing strategies for examining and comparing normal and abnormal mouse embryonic development and anatomy. In this study, we have explored the use of magnetic resonance microscopy as a tool for these purposes. Techniques for the fixation, embedding, perfusion, and image acquisition of mouse embryos are described. The perfusion of bovine serum albumin-diethylenetriamine pentaacetic anhydride-gadolinium as a contrast agent enhances images of the developing embryonic vasculature during critical stages of organogenesis and allows for comparisons when embryos have been treated with teratogens such as retinoic acid. The acquired three-dimensional data sets are available for archiving, distributing, and postacquisition manipulations such as computer segmentation of anatomical structures.

Utility of postmortem magnetic resonance imaging in clinical neuropathology

Over 200 brains were examined by postmortem magnetic resonance imaging to determine the utility of this imaging procedure as an adjunct to the standard postmortem examination of the brain and spinal cord. One unembalmed cadaver was also studied using a conventional 1.5-tesla (T) field-strength unit, and three formalin-fixed sections of the hippocampus were imaged using a high field-strength (7.0-T) prototype imaging system. The postmortem magnetic resonance images proved to be an invaluable aid that complemented the standard pathologic examination of the brain and spinal cord. The compelling advantages of this postmortem radiographic procedure included the three-dimensional aspects of the images; the ability to detect mineral (ie, iron) deposits; small focal lesions such as hemorrhages or infarcts; and the ability to evaluate the extent of cerebral edema. For the same reasons, as well as its archival potential for documenting the topographic distribution of pathologic processes, this technique has great promise for forensic cases. High field-strength (7.0-T) imaging brought the resolution of magnetic resonance to the microscopic level and reaffirmed the potential value of magnetic resonance imaging for diagnostic and investigative studies in which both the histologic and fine radiologic features of lesions are of interest.

Minoxidil sulfation in the hair follicle

The in vivo model which may be the most accurate for the ability to predict hair growth in humans, and which was utilized in the preclinical development of minoxidil, is the adult stumptailed macaque. Previous reports have suggested that the enzyme activity which accounts for the activation of minoxidil, i.e., minoxidil sulfotransferase, is present in skin. We have demonstrated that scalp skin from the stumptailed macaque contains minoxidil sulfotransferase activity, and further with dissection of that scalp skin into epidermis, dermis and hair follicle, most of sulfotransferase activity was present in the follicle. Sulfotransferase activity in the hair follicle in freeze-dried scalp skin sections from 9 stumptailed macaques ranged from 47 to 84% of the total (mean 61 +/- 12%). Much less minoxidil sulfotransferase activity was measured in the epidermis (mean 18 +/- 11%, with a range of 2-37%) and the dermis (mean 21 +/- 8%, with a range of 4-35%) of these scalp sections. These results indicate that the scalp skin from the stumptailed macaque contains minoxidil sulfotransferase activity and this activity is largely localized in the hair follicle which may account for its ability to stimulate hair growth in this animal model.

Mathematical modeling of ligaments and tendons

Ligaments and tendons serve a variety of important functions in maintaining the structure of the human body. Although abundant literature exists describing experimental investigations of these tissues, mathematical modeling of ligaments and tendons also contributes significantly to understanding their behavior. This paper presents a survey of developments in mathematical modeling of ligaments and tendons over the past 20 years. Mathematical descriptions of ligaments and tendons are identified as either elastic or viscoelastic, and are discussed in chronological order. Elastic models assume that ligaments and tendons do not display time dependent behavior and thus, they focus on describing the nonlinear aspects of their mechanical response. On the other hand, viscoelastic models incorporate time dependent effects into their mathematical description. In particular, two viscoelastic models are discussed in detail; quasi-linear viscoelasticity (QLV), which has been widely used in the past 20 years, and the recently proposed single integral finite strain (SIFS) model.

Reduction of ringing and blurring artifacts in fast spin-echo imaging

A simple method was devised to reduce ringing and blurring artifacts caused by discontinuous T2 weighting of k-space data in fast spin-echo magnetic resonance (MR) imaging. The method demodulates the weighting function along the phase-encoding direction by using multiple T2 values derived from a set of non-phase-encoded echoes obtained from an extra excitation. The performance of this method was evaluated by computer simulations and experiments, which confirmed its capability of effectively reducing or, in some cases, even completely removing the ringing and blurring artifacts. The results also show that the proposed method produces better results than other artifact reduction methods. The method is particularly useful at high magnetic field strengths (7.1-9.4 T) and with strong gradients (> 20 G/cm) used in MR microscopy, in which the apparent T2 values are short for most tissues. The authors expect that the proposed method will find useful applications in various fast spin-echo pulse sequences.

Diffusion-weighted MR microscopy with fast spin-echo

A diffusion-weighted fast spin-echo (FSE) imaging sequence for high-field MR microscopy was developed and experimentally validated in a phantom and in a live rat. Pulsed diffusion gradients were executed before and after the initial 180 degrees pulse in the FSE pulse train. This produced diffusion-related reductions in image signal intensity corresponding to gradient ("b") factors between 1.80 and 1352 s/mm2. The degree of diffusion weighting was demonstrated to be independent of echo train length for experiments using trains up to 16 echoes long. Quantitative measurements on a phantom and on a live rat produced diffusion coefficients consistent with literature values. Importantly, the eight- to 16-fold increase in imaging efficiency with FSE was not accompanied by a significant loss of spatial resolution or contrast. This permits acquisition of in vivo three-dimensional data in time periods that are appropriate for evolving biological processes. The combination of accurate diffusion weighting and high spatial resolution provided by FSE makes the technique particularly useful for MR microscopy.

High-field MR microscopy using fast spin-echoes

Fast spin-echo imaging has been investigated with attention to the requirements and opportunities for high-field MR microscopy. Two- and three-dimensional versions were implemented at 2.0 T, 7.1 T, and 9.4 T. At these fields, at least eight echoes were collectable with a 10 ms TE from fixed tissue specimens and living animals, giving an eightfold improvement in imaging efficiency. To reduce the phase-encoding gradient amplitude and its duty cycle, a modified pulse sequence with phase accumulation was developed. Images obtained using this pulse sequence exhibited comparable signal-to-noise (SNR) to those obtained from the conventional fast spin-echo pulse sequences. Signal losses due to imperfections in RF pulses and lack of phase rewinders were offset in this sequence by reduced diffusion losses incurred with the gradients required for MR microscopy. Image SNR, contrast, edge effects and spatial resolution for three k-space sampling schemes were studied experimentally and theoretically. One method of sampling k-space, 4-GROUP FSE, was found particularly useful in producing varied T2 contrast at high field. Two-dimensional images of tissue specimens were obtained in a total acquisition time of 1 to 2 min with in-plane resolution between 30 to 70 microns, and 3D images with 256(3) arrays were acquired from fixed rat brain tissue (isotropic voxel = 70 microns) and a living rat (isotropic voxel = 117 microns) in approximately 4.5 h.

Enhanced in vitro hair growth at the air-liquid interface: minoxidil preserves the root sheath in cultured whisker follicles

Inasmuch as hair follicles are difficult to maintain in culture, the study of hair biology using cultured hair follicles has met with only limited success. In our attempts to solve the problem of follicle degeneration, we cultured follicles at the air-surface interface on a modified collagen matrix (Gelfoam). In follicles cultured at the air-surface or submerged, we examined follicular morphology, hair shaft growth, sulfotransferase levels, cysteine incorporation, an expression of a tissue inhibitor of metalloproteinase (TIMP), and ultra-high sulfur keratin (UHSK). Follicles cultured at the air-liquid interface produced a 2.7-fold increase in hair growth and maintained an anagen-like morphology. Substrates such as nylon mesh seeded with fibroblasts, Full Thickness Skin, or 5-microns polycarbonate filter also supported hair growth, whereas Gelfilm, GF-A glass filter, filter paper, or 1-micron polycarbonate filter did not. The UHSK expression was significantly higher in the air-liquid interface cultures compared to the submerged culture. Several potassium channel openers, including minoxidil, a minoxidil analog, and the pinacidil analog (P-1075), all stimulated significant cysteine incorporation in follicles. Minoxidil and its analog specifically preserved the follicular root sheath, in contrast to P-1075 which did not, indicating a difference in the two drug types. The preservation of the root sheath was measured by increased TIMP expression and sulfotransferase activity and indicates that the root sheath is a target tissue for minoxidil. Our results show that follicles cultured at the air-liquid interface maintain a better morphology and produced greater hair growth than follicles cultured on tissue culture plastic.

Oscillometric blood pressures in the arm, thigh, and calf in healthy children and those with aortic coarctation

Comparing blood pressure (BP) obtained in the arm with that obtained in the thigh or calf is important in the diagnosis of aortic coarctation. However, normative mean and range of differences in BP between the arm and lower extremity sites are not available for normal children. It is also not known how accurately the differences in BP between the arm and the lower extremity sites predict the pulsed Doppler estimation of systolic pressure (SP) gradient across an aortic coarctation. To resolve these questions, the authors obtained two BP measurements by an oscillometric (Dinamap) method in the arm, thigh, and calf in 74 healthy children aged 4 to 16 years. Oscillometric BP was also obtained in 21 children aged 3 to 17 years with preoperative or postoperative aortic coarctation and BP gradients were compared with that estimated by the pulsed Doppler method. Overall, SP was higher in the thigh and calf than in the arm. The gradients in SP expressed as arm SP minus calf SP [S(A-C)] and arm SP minus thigh SP [S(A-T)] were significantly greater in children 4 through 8 years old than in those 9 to 16 years old. The S(A-C) was -9.3 (+/- 7.4 SD) mm Hg in the 4- through 8-year group and -5.0 (+/- 6.9 SD) mm Hg in the 9- to 16-year group. The S(A-T) was -7.1 (+/- 6.8 SD) mm Hg in the 4- through 8-year group and -2.4 (+/- 7.7 SD) mm Hg in the 9- to 16-year group.(ABSTRACT TRUNCATED AT 250 WORDS)

Histology by magnetic resonance microscopy

Magnetic resonance microscopy (MRM) has advanced from a technical challenge to a practical tool in a wide range of basic sciences. This article focuses on the use of MRM as a tool for histological studies. The technical challenges of limited signal to noise have been overcome by improved radio-frequency (rf) coil design and 3DFT encoding with large arrays. Resolution limits imposed by motion in in vivo studies have been overcome by improved physiologic monitoring and control and projection encoding. Integration of technologies now permits routine studies in vivo down to 50 microns. MRM has also been applied to in vitro studies of fixed tissues where absence of motion allows studies down to 10 microns. The nondestructive nature of the technique allows repeated studies of the same sample, retrospective studies through any arbitrary plane, registered studies using different contrast mechanisms, and examination of valuable specimens. The many and unique proton contrasts provided by MRM, i.e., T1, T2, and diffusion weighting, permit direct examination of the state of water in tissues, something not possible with other microscopic techniques. Finally, the inherent three-dimensional nature of MRM allows acquisition of perfectly registered isotropic 3D arrays that, when displayed with appropriate visualization tools, provide new perspectives to histologic examination. The technology of MRM continues to develop rapidly. New pulse sequences are reducing acquisition times. New computer architectures allow larger arrays. A new class of superconducting rf probe has increased the signal to noise ratio by 10 times. These developments promise routine use of MRM in histology studies with resolution to 1 micron in the near future.

A high-temperature superconducting receiver for nuclear magnetic resonance microscopy

A high-temperature superconducting-receiver system for use in nuclear magnetic resonance (NMR) microscopy is described. The scaling behavior of sources of sample and receiver-coil noise is analyzed, and it is demonstrated that Johnson, or thermal, noise in the receiver coil is the factor that limits resolution. The behavior of superconductors in the environment of an NMR experiment is examined, and a prototypical system for imaging biological specimens is discussed. Preliminary spin-echo images are shown, and the ultimate limits of the signal-to-noise ratio of the probe are investigated.