Biomedical subjects

Ronald R Price

Publications and source records attributed to Ronald R Price.

18 recordsLinked to original sources

PubMed2004

Colored thin films for specific metal ion detection.

This paper describes the investigation of chitosan and poly(allylamine) (PAH) for the creation of a multi-film, color-based dipstick for the detection of metal ions in solution. Thin, colored films of chitosan and PAH cross-linked with hexamethylene 1,6-di(aminocarboxysulfonate) (HDACS) are created where color is due to film thickness and optical interference effects. The films are investigated for their ability to selectively detect aqueous metal ions via changes in thickness and/or color. Chitosan-HDACS films were selective for Cr(VI) over all other metal ions tested including Cr(acac)3 and Cr(NO3)3 x 9H2O, and PAH-HDACS films were selective for Cu(II) and Cu(I) salts over all other metal ions tested. The irreversible, selective changes due to metal ion solutions were not caused by varying the pH. Potomac River water was also tested using the two films, with results indicating the presence of Cu(II) in the aqueous sample.

Allylamine↗

PubMed2004

MR safety.

Explore the source record for details and available documents.

Humans↗

PubMed2004

Characterizing changes in MR images with color-coded Jacobians.

Image registration is the process of establishing spatial correspondence between two images or between two image volumes. Registration can be achieved by rigid, elastic, or a combination of rigid and elastic transforms that attempt to bring the two images into coincidence. A rigid transform accounts for differences in positioning and an elastic transform describes deformations due to differences in tissue properties, temporal changes due to growth or atrophy, or differences between individuals. Deformation-based morphometry uses the resulting deformation fields from these transforms to evaluate differences between the images being registered. Three methods of registration were evaluated: rigid (affine) transformation, elastic optical flow transformation, and elastic spline transformation. All three methods produce vector deformation fields that map each point in one image to a point in the other image. A 12-color map of the transformation Jacobian was used to represent local volume changes. Using the three registration methods, color-mapped Jacobians were determined using a simulated three-dimensional block with known translation, rotation, expansion, contraction, and intensity modulations. Color-coded Jacobians were also generated for experimentally measured magnetic resonance image volumes of water-filled balloons and 7-year-old twin boys. Color-coded Jacobians overlaid on anatomical images provide a convenient method to identify regional tissue expansion and contraction.

Algorithms↗

PubMed2004

The effect of sensorimotor activation on functional connectivity mapping with MRI.

The correlations in the fluctuations in the blood oxygenation level-dependent (BOLD) MRI signal between anatomically distinct regions of the cortex that are known components of functional systems have been previously studied as possible indicators of functional connectivity. The objective of this study was to examine the effect of sensorimotor brain activity, as assessed by task-based functional magnetic resonance imaging (fMRI), on functional connectivity indices in the same region. Regions of activation for sequential finger motion were determined using a task-based, block-design fMRI study. Functional connectivity measurements based on interregional correlations were acquired at rest and during continuous, sequential finger motion. Connectivity indices were determined using normalized mean correlations within and between three regions of interest activated for the finger motion task. Connectivity indices were also determined for a control region that was not activated for the task. Continuous motor tasks performed during BOLD measurements did not significantly affect the functional connectivity as compared to the connectivity at rest within or between regions known to be activated by the task. However, there appeared to be a trend suggesting a slight reduction in connectivity indices during the motor task. The connectivity within and between those areas not activated for the task remained unchanged between conditions. These results suggest that in the motor system investigated, the recruitment of neurons to perform a specific task may moderately reduce the degree of hemodynamic coupling within and between regions.

Adult↗

PubMed2004

Resting functional MRI with temporal clustering analysis for localization of epileptic activity without EEG.

We report on the methods and initial findings of a novel noninvasive technique, resting functional magnetic resonance imaging (fMRI) with temporal clustering analysis (TCA), for localizing interictal epileptic activity. Nine subjects were studied including six temporal lobe epilepsy (TLE) patients with confirmed localization indicated by successful seizure control after resection. The remaining three subjects had standard presurgical evaluations with inconsistent results or suspected extratemporal lobe foci. Peaks of activity, presumably epileptic, were detected in all nine subjects, using the resting functional MRI with temporal clustering analysis. In all six patients who underwent resective surgery, the fMRI with temporal clustering analysis accurately determined the epileptogenic hippocampal hemisphere (P = 0.005). In the three subjects without confirmed localization, the technique determined regions of activity consistent with those determined by the presurgical assessments. Though more studies are required to validate this technique, the results demonstrate the potential of the resting fMRI with temporal clustering technique to detect and localize epileptic activity without the need for simultaneous electroencephalography (EEG). The greatest potential benefit of this technique will be in the evaluation of patients with suspected extratemporal lobe epilepsy and patients whose standard assessments are discordant.

Adolescent↗

PubMed2004

Phantom validation of coregistration of PET and CT for image-guided radiotherapy.

Radiotherapy treatment planning integrating positron emission tomography (PET) and computerized tomography (CT) is rapidly gaining acceptance in the clinical setting. Although hybrid systems are available, often the planning CT is acquired on a dedicated system separate from the PET scanner. A limiting factor to using PET data becomes the accuracy of the CT/PET registration. In this work, we use phantom and patient validation to demonstrate a general method for assessing the accuracy of CT/PET image registration and apply it to two multi-modality image registration programs. An IAEA (International Atomic Energy Association) brain phantom and an anthropomorphic head phantom were used. Internal volumes and externally mounted fiducial markers were filled with CT contrast and 18F-fluorodeoxyglucose (FDG). CT, PET emission, and PET transmission images were acquired and registered using two different image registration algorithms. CT/PET Fusion (GE Medical Systems, Milwaukee, WI) is commercially available and uses a semi-automated initial step followed by manual adjustment. Automatic Mutual Information-based Registration (AMIR), developed at our institution, is fully automated and exhibits no variation between repeated registrations. Registration was performed using distinct phantom structures; assessment of accuracy was determined from registration of the calculated centroids of a set of fiducial markers. By comparing structure-based registration with fiducial-based registration, target registration error (TRE) was computed at each point in a three-dimensional (3D) grid that spans the image volume. Identical methods were also applied to patient data to assess CT/PET registration accuracy. Accuracy was calculated as the mean with standard deviation of the TRE for every point in the 3D grid. Overall TRE values for the IAEA brain phantom are: CT/PET Fusion = 1.71 +/- 0.62 mm, AMIR = 1.13 +/- 0.53 mm; overall TRE values for the anthropomorphic head phantom are: CT/PET Fusion = 1.66 +/- 0.53 mm, AMIR = 1.15 +/- 0.48 mm. Precision (repeatability by a single user) measured for CT/PET Fusion: IAEA phantom = 1.59 +/- 0.67 mm and anthropomorphic head phantom = 1.63 +/- 0.52 mm. (AMIR has exact precision and so no measurements are necessary.) One sample patient demonstrated the following accuracy results: CT/PET Fusion = 3.89 +/- 1.61 mm, AMIR = 2.86 +/- 0.60 mm. Semi-automatic and automatic image registration methods may be used to facilitate incorporation of PET data into radiotherapy treatment planning in relatively rigid anatomic sites, such as head and neck. The overall accuracies in phantom and patient images are < 2 mm and < 4 mm, respectively, using either registration algorithm. Registration accuracy may decrease, however, as distance from the initial registration points (CT/PET fusion) or center of the image (AMIR) increases. Additional information provided by PET may improve dose coverage to active tumor subregions and hence tumor control. This study shows that the accuracy obtained by image registration with these two methods is well suited for image-guided radiotherapy.

Algorithms↗

PubMed2003

FDG PET in the follow-up management of patients with newly diagnosed Hodgkin and non-Hodgkin lymphoma after first-line chemotherapy.

PURPOSE: The purpose of this study was to evaluate the accuracy of PET imaging for predicting recurrence of disease and determining fields of radiation therapy for patients with lymphoma after first-line chemotherapy. METHODS AND MATERIALS: The study population included 40 patients with lymphoma, newly diagnosed, staged and treated with either chemotherapy alone or combined modality therapy at this institution. PET findings were correlated with CT findings and radiation ports. Treatment and follow-up course were analyzed to determine patterns of failure. RESULTS: Twenty-eight of 40 patients (70%) were treated with chemotherapy alone, 12 of 40 (30%) were treated with combined modality therapy. Of the patients who received chemotherapy alone, 21 (75%) had a negative follow-up PET scan at the original site of disease, and 5 of these 21 (24%) recurred within the original site of disease. Of the patients who received combined modality therapy, 10 (83%) had a negative follow-up PET scan at the original site of disease and none recurred within the original site of disease. CONCLUSIONS: A negative PET scan after completion of therapy does not exclude the presence of residual microscopic disease and does not indicate complete remission. A higher recurrence rate in patients who were treated with chemotherapy alone compared with combined modality therapy suggests that some of these patients may benefit from aggressive radiation therapy planned at initial staging. The radiation treatment volumes may be better planned from the initial staging PET study because a negative follow-up PET scan after chemotherapy cannot exclude residual microscopic disease.

Adolescent↗

PubMed2003

Proton MR spectroscopic studies of chronic alcohol exposure on the rat brain.

PURPOSE: To better understand the long-term pathophysiologic mechanisms of alcoholism-related organic brain damage by serially assessing brain metabolites in chronically exposed rats using both in vivo magnetic resonance spectroscopy (MRS) and high-resolution nuclear magnetic resonance (NMR) from brain extracts. MATERIALS AND METHODS: The alcoholic regimen was continued up to 60 weeks. In vivo proton MRS studies were performed at 200 MHz using a small animal imaging/spectrometer. In vitro rat brain extracts were also examined using a 500 MHz vertical bore magnet. Comparison measurements were also obtained in an age-matched control group. RESULTS: In vivo results showed that there is a significant increase in the Cho/NAA ratio in the chronic alcohol-exposed group that reached a maximum around 16 weeks. After 44 weeks of alcohol exposure, Cho/NAA in the alcohol group decreased significantly from its maximum value to a value that was significantly lower than those from the control groups. Brain extract studies demonstrated that PC and GPC were the main components responsible for the observed in vivo spectral changes after 16 and 60 weeks of alcohol consumption, respectively. CONCLUSION: The fluctuation of choline-containing metabolites during alcohol intoxication could explain sometimes seemingly conflicting and confusing results from MRS studies in human and animal studies in which the duration of alcohol consumption and amount are varied widely.

Alcoholism↗

PubMed2003

Experimental model for functional magnetic resonance imaging of somatic sensory cortex in the unanesthetized rat.

Functional magnetic resonance imaging (fMRI) has evolved into a method widely used to map neural activation in the human brain. fMRI is a method for recording blood oxygen level-dependent (BOLD) signals. These signals change with local cerebral blood flow coupled to neural activity. However, the relationship between BOLD signals and neural function is poorly understood and requires the development of animal models. Here we use an unanesthetized rat preparation to study BOLD responses to whisker stimulation in somatic sensory barrel cortex. Five rats were trained to tolerate restraint in a holder and fMRI noise with positive reinforcement. For maximal immobilization, the head was fastened to the holder with nuts screwed on threaded bolts attached to the head. On scanning day, residual stress was alleviated with injections of diazepam, and the rats were restrained in the holder and transferred into the scanner. After >75 min to allow the tranquilization to abate, structural images were acquired from three coronal brain slices. Subsequently, functional images were taken utilizing 4-min epochs without stimulation alternated with equivalent epochs during which the right caudal whiskers were stimulated with three air puffs/s. After 4 weeks, fMRI could be repeated in four rats. In seven of the nine functional runs, head motion was minimal and whisker stimulation resulted in a statistically significant (P </= 0.05) increase in BOLD signal in barrel cortex predominantly on the contralateral side. The results provide encouragement that long-term fMRI studies on cerebral function in unanesthetized rats may be feasible with our procedure.

Animals↗

PubMed2003

Brain fMRI activation associated with self-paced finger tapping in chronic alcohol-dependent patients.

BACKGROUND: Fine and gross motor dysfunction in chronic alcoholic patients is prevalent, but not extensively studied. Brain autopsy studies of brain regions involved in motor movements indicate cerebellum and frontal lobes are particularly sensitive to alcohol-induced damage, in contrast to motor cortex. METHODS: Using functional magnetic resonance imaging (fMRI), we compared the pattern of activation of the cerebral cortex and cerebellum during repetitive, self-paced dominant (DH) and nondominant (NDH) index finger tapping in eight uncomplicated alcohol-dependent patients after approximately 2 weeks of abstinence and in nine normal controls. RESULTS: Whereas alcoholic patients tapped significantly more slowly than normal controls, a greater percentage of pixels were activated in the ipsilateral cortex during DH tapping. Furthermore, alcoholics tapped significantly less efficiently (tapping rate divided by percent pixels activated [weighted by pixel intensity] in a given region of interest [ROI]) than normal controls in every ROI examined while using DH, but only in ipsilateral hemi-cerebellum using NDH. Finally, the alcohol-dependent patients did not demonstrate the greater mean pixel activation, percentage activated pixels, and lesser activation efficiency in the ipsilateral cortex during NDH compared to DH tapping that was observed in the normal control group. CONCLUSIONS: These findings are compatible with motor inefficiency and compensatory alterations of cortical-cerebellar circuits. Further studies are needed to determine whether these deficits recover with prolonged abstinence and how they relate to cognitive inefficiency throughout the clinical course of alcoholism.

Adult↗

PubMed2003

Dual focal-spot imaging for phase extraction in phase-contrast radiography.

The purpose of this study was to evaluate dual focal spot imaging as a method for extracting the phase component from a phase-contrast radiography image. All measurements were performed using a microfocus tungsten-target x-ray tube with an adjustable focal-spot size (0.01 mm to 0.045 mm). For each object, high-resolution digital radiographs were obtained with two different focal spot sizes to produce matched image pairs in which all other geometric variables as well as total exposure and tube kVp were held constant. For each image pair, a phase extraction was performed using pixel-wise division. The phase-extracted image resulted in an image similar to the standard image processing tool commonly referred to as "unsharp masking" but with the additional edge-enhancement produced by phase-contrast effects. The phase-extracted image illustrates the differences between the two images whose imaging parameters differ only in focal spot size. The resulting image shows effects from both phase contrast as well as geometric unsharpness. In weakly attenuating materials the phase-contrast effect predominates, while in strongly attenuating materials the phase effects are so small that they are not detectable. The phase-extracted image in the strongly attenuating object reflects differences in geometric unsharpness. The degree of phase extraction depends strongly on the size of the smallest focal spot used. This technique of dual-focal spot phase-contrast radiography provides a simple technique for phase-component (edge) extraction in phase-contrast radiography. In strongly attenuating materials the phase-component is overwhelmed by differences in geometric unsharpness. In these cases the technique provides a form of unsharp masking which also accentuates the edges. Thus, the two effects are complimentary and may be useful in the detection of small objects.

Algorithms↗

PubMed2003

Quantification of the effect of system and object parameters on edge enhancement in phase-contrast radiography.

The purpose of this study was to evaluate the effects of system parameters (focal spot size, tube voltage, geometry, detector resolution, and image noise) and object characteristics (edge gradient/ shape, composition, thickness, and overlying attenuating material) upon the edge enhancement effect in phase-contrast radiography. Each variable of interest was adjusted and images of a 3 mm lucite phantom were obtained with the other variables remaining constant. A microfocus x-ray source coupled to a CCD camera with an intensifying screen was used to acquire the digital images. Two parameters of image analysis were used to quantify the effects. The edge enhancement index (EEI) was used to measure the absolute degree of edge enhancement, while the edge enhancement to noise ratio (EE/N) was used to measure the conspicuity of the edge enhancement relative to image noise. Little effect on EEI was seen from tube voltage, object thickness, overlying attenuating material, while focal spot size and system geometry demonstrated measurable effects upon the degree of edge enhancement. It was also shown that while the edge enhancement effect over straight edges is highly dependent upon how the edge aligns with the x-ray beam, rounded edges, which better model biological objects, do not suffer from this dependence and the EEI reaches its maximal level at any alignment. Decreasing detector resolution diminished the EEI slightly, but even with pixel sizes of 0.360 x 0.360 mm edge enhancement effects were readily visible. The effect of image noise on EE/N was evaluated using different exposure times showing an expected improvement with longer exposure time with EE/N approaching a plateau at 5 min. Many of the parameters that will go into the design of a future PC-R imaging system have been quantified in terms of their effect on the degree of edge enhancement in the acquired image. These results, taken together, indicate that either a specimen or even clinical breast imaging system could be created with currently available technology. The major limitation to a clinical system would be the low x-ray flux from the microfocal x-ray source.

Pattern Recognition, Automated↗

PubMed2002

Longitudinal brain metabolic characterization of chronic alcoholics with proton magnetic resonance spectroscopy.

BACKGROUND: Proton magnetic resonance spectroscopy may elucidate the molecular underpinnings of alcoholism-associated brain shrinkage and the progression of alcohol dependence. METHODS: Using proton magnetic resonance spectroscopy, we determined absolute concentrations of -acetylaspartate (NAA), creatine/phosphocreatine (Cr), and choline (Cho)-containing compounds and -inositol (mI) in the anterior superior cerebellar vermis and frontal lobe white matter in 31 alcoholics and 12 normal controls. All patients were examined within 3 to 5 days of their last drink. Patients who did not relapse were again studied after 3 weeks and 3 months of abstinence by using an on-line repositioning technique that allows reliable localization of volumes of interest (VOIs). RESULTS: At 3 to 5 days after the last drink, frontal white matter metabolite concentrations were not significantly different from those of normal controls, whereas brain tissue in the VOI was reduced. Cerebellar [NAA] and [Cho] and brain and cerebellar volumes were decreased, but [Cr], [mI], and VOI brain tissue volume were not significantly different. Eight patients relapsed before 3 weeks (ER), 12 relapsed between 3 weeks and 3 months (LR), and 11 did not relapse (NR) during 3 months. Cerebellar [NAA] was reduced only in ER patients, despite the fact that ER patients drank for significantly fewer years and earlier in life than LR or NR patients. After 3 months, in the 11 continuously abstinent patients, cerebellar [NAA] and brain and cerebellar volumes increased; cerebellar [Cho], [Cr], and [mI] and VOI brain tissue did not change significantly. CONCLUSIONS: Decreased [NAA] and [Cho] in cerebellar vermis indicate a unique sensitivity to alcohol-induced brain injury. Cerebellar [NAA] increased with abstinence, but reduced [Cho] persisted beyond 3 months. Further studies are needed to determine whether low cerebellar [NAA] is a risk factor for, or consequence of, malignant, early-onset alcoholism.

Adult↗

PubMed2002

Quantification of the effect of kvp on edge-enhancement index in phase-contrast radiography.

This study was performed to measure the dependence of edge-enhancement in polychromatic phase-contrast radiography on x-ray tube operating voltage. Measurements of edge enhancement were made at tube voltages from 40 to 86 kVp using a tungsten anode x-ray tube with a nominal focal spot size of 100 micrometers. A relatively weak attenuating, sharp edge consisting of a thin lucite sheet (3 mm) in air was imaged utilizing phase-contrast radiography (PC-R). PC-R images were acquired at different radiographic techniques in which x-ray tube voltage was varied from 40 to 86 kVp. The image receptor was a single emulsion x-ray mammography cassette. Optical density profiles across the edge of the object were obtained using a film digitizer and edge-enhancement indices were calculated. Increasing kVp resulted in a gradual decrease of the edge-enhancement index. Even at the highest kVp (86), however, important edge-enhancement effects were evident. While there is some degradation in the edge-enhancement effect of phase-contrast radiography at higher kVps, the decrease from 40 to 86 kVp is relatively small (11%). Our results suggest that further investigation into the role of phase-contrast imaging at higher kVp values for the purpose of patient dose reduction while still realizing the advantage of phase-contrast effects for improved soft-tissue detectability is warranted.

Image Processing, Computer-Assisted↗

PubMed2002

Practical aspects of functional MRI (NMR Task Group #8).

Functional MR imaging (fMRI) based upon the Blood Oxygen Level Dependent (BOLD) effect is currently an important new tool for understanding basic brain function and specifically allowing the correlation of physiological activity with anatomical location without the use of ionizing radiation. The clinical role of fMRI is still being defined and is the subject of much research activity. In this report we present the underlying physical, technical and mathematical principals of BOLD fMRI along with descriptions of typical applications. Our purpose in this report is to provide, in addition to basic principles, an insight into the aspects of BOLD imaging, which may be used by the medical physicist to assist in the implement of fMRI procedures in either a hospital or research environment.

Brain↗

PubMedDate not supplied

Targeted molecular imaging agents for cellular-scale bimodal imaging.

Molecular imaging is a powerful tool that has the ability to elucidate biochemical mechanisms and signal the early onset of disease. Overexpression of the peripheral benzodiazepine receptor (PBR) has been observed in a variety disease states, including glioblastoma, breast cancer, and Alzheimer's disease. Thus, the PBR could be an attractive target for molecular imaging. In this paper, the authors report cellular uptake and multimodal (MRI and fluorescence) imaging of PBR-overexpressing C6 glioblastoma (brain cancer) cells using a cocktail administration approach and a new PBR targeted lanthanide chelate molecular imaging agent.

Animals↗

PubMedDate not supplied

Chitosan cross-linking with a water-soluble, blocked diisocyanate. 1. Solid state.

The present investigation focuses on the synthesis and application of a cross-linking agent that is compatible with the solubility characteristics of chitosan. A water-soluble, blocked-diisocyanate was prepared as a bisulfite adduct to 1,6-hexamethylene diisocyanate, which proved to be stable for several weeks in aqueous, acidic chitosan solutions at room temperature. Thermal cross-linking of chitosan as cast, dried films was investigated by varying the NCO/NH(2) ratio from 0.0 to 1.2. Spectroscopic (IR), thermal (TGA), swelling, and structural (WAXD) studies indicated that chitosan was cross-linked in a concentration-dependent manner under mild thermal conditions: 60 degrees C for 24 h. Cross-linking inefficiency was concluded to be due to lack of mobility of the reacting species in the solid state. In a preliminary study, the enzymatic degradation with Chitinase (E. C. 3.2.1.14) from Streptomyces griseus was found to be the greatest for non-crosslinked chitosan, followed by chitin, and then by cross-linked samples.

Biodegradation, Environmental↗

PubMedDate not supplied

Chitosan cross-linking with a water-soluble, blocked diisocyanate. 2. Solvates and hydrogels.

A water-soluble, blocked diisocyante was used to cross-link chitosan under various degrees of solvation, including hydration to form hydrogels. Thermal cross-linking of films cast from various amounts of organic cosolvents was found to increase with increased level of cosolvent up to a solvation level of 17% (w/w) and to be more efficient than for films prepared without cosolvent. Rheological studies revealed that gel modulus increased and gel time decreased with increasing cross-linker content and that gelation kinetics were consistent with a process having an activation energy of 103 kJ/mol. Swelling of hydrogels indicated that, even at high levels of hydration, the increased molecular mobility of reactants allowed for efficient network formation in a concentration-dependent manner. The extent of solvation via equilibrium swelling correlated well with degradative properties of chitosan networks in the presence of Chitinase (E. C. 3.2.1.14) from Streptomyces griseus with stability increasing with decreasing swelling (i.e., increased cross-linking).

Biodegradation, Environmental↗