Search PubMed⌕ Search

Biomedical subjects

R A Kruger

Publications and source records attributed to R A Kruger.

At least 19 recordsLinked to original sources
PubMed2000

Breast cancer in vivo: contrast enhancement with thermoacoustic CT at 434 MHz-feasibility study.

The authors performed thermoacoustic computed tomography (CT) with 434-MHz radio waves in five patients with documented breast cancer. Three of the patients underwent imaging before chemotherapy was initiated and two at the conclusion of their primary chemotherapy. In the former three patients, thermoacoustic CT demonstrated contrast enhancement in the region of the tumor. In the latter two patients, no contrast enhancement was seen, and pathologic examination after surgical resection of the area of original tumor confirmed complete remission of disease.

Acoustics↗
PubMed1999

Thermoacoustic computed tomography--technical considerations.

We have constructed a thermoacoustic computed tomography scanner for imaging soft tissue in the human body. Thermoacoustic signals are induced in soft tissue by irradiation with 434 MHz rf energy. The thermoacoustic signals are detected by an array of transducers mounted on a hemispherical bowl. A three-dimensional, filtered backprojection algorithm is used to reconstruct rf absorption patterns within soft tissue. We have demonstrated soft tissue differentiation sufficient to delineate the normal internal structures of an excised lamb kidney using safe levels of rf radiation.

Acoustics↗
PubMed1999

Thermoacoustic CT with radio waves: a medical imaging paradigm.

The authors evaluated images obtained with a prototypic thermoacoustic computed tomographic (CT) scanner constructed for use at 434 MHz, a promising radio frequency for detecting breast cancer. In one excised porcine kidney, acoustic energy emanating from the kidney was detected with transducers. The resultant electric signals were used to create a three-dimensional data set. Two-dimensional images reconstructed in multiple planes were compared with state-of-the-art T1- and T2-weighted magnetic resonance images. The renal outline, parenchyma, and collecting system were clearly delineated on the thermoacoustic CT images.

Acoustics↗
PubMed1996

World Wide Web interface to digital imaging and communication in medicine-capable image servers.

As a trial project, the Indiana University Department of Radiology has develop[ed a low-cost manner of distributing radiological images throughout a medical environment using the World Wide Web (WWW). The interface requires the user to have a WWW-browser client, such as Netscape, running on UNIX, PC, or Macintosh platforms. A forms-based interface allows the user to query several DICOM-capable machines at the machine, patient, study, series, and image levels. Once an image transfer is initiated, images are prewindowed from 16- to 8-bits, compressed using public domain Joint Photographic Expert Group (JPEG) compression routines, transferred to the WWW client program, and decompressed and displayed using a locally selected image viewing program. At the currently implemented level of compression (75% quality), the entire fetch-transform-JPEG-display process takes 2 to 5 seconds over Ethernet, depending on the platform used.

Computer Communication Networks↗
PubMed1996

Image intensifier-based computed tomography volume scanner for angiography.

RATIONALE AND OBJECTIVES: A prototype volume computed tomography (CT) system for use in angiography was designed, constructed, and tested. The system consisted of a fixed X-ray tube, a conventional image intensifier (II) coupled to a charge-coupled device camera, and a computer-controlled turntable on which phantoms were placed. We wanted to predict, through phantom studies, the imaging performance of an II-based volume CT for direct three-dimensional (3D) reconstruction of vascular structures. METHODS: To explore the imaging performance of the system for reconstructing a vascular structure, two sets of projection images of a vascular phantom, acquired over 250 projection angles with two different-sized IIs, were digitized and used for a direct 3D conebeam reconstruction. The signal-to-noise ratio (SNR) of each reconstructed image was measured. From these measurements, image quality was accessed as a function of the number of reconstructions averaged and the different orientations. The spatial resolution limits of the system were measured from the 3D reconstructed images of a specially designed resolution phantom for different orientations and locations. RESULTS: The measured SNRs of all direct 3D reconstruction images were reasonably good, and back-ground noise levels measured from 3D reconstruction images were almost 30 Hounsfield units. The measured spatial resolution of the system was 0.5 line pairs per millimeter. However, spatial resolution was reduced around the edge of the II to nearly half that measured in the central area of the field of view. CONCLUSION: An II-based volume CT scanner can produce direct 3D reconstructions of vascular structures with good image quality for intraarterial angiography.

Angiography↗
PubMed1996

Dual-slice spiral versus single-slice spiral scanning: comparison of the physical performance of two computed tomography scanners.

In this paper we deal with two types of spiral scanners; one is a single-slice spiral scanner, while the other employs dual-slice technology into spiral scanning. Physical performance parameters, including image noise, contrast resolution, spatial resolution (transversal and longitudinal), and radiation exposure are measured. Computer simulations based on two interpolation methods (180 degrees and 360 degrees linear interpolation) are also used in evaluating the slice-sensitivity profile (SSP) and noise. The results show that the noise behaves in the same way for both types of scanners. The noise change, relative to that of the standard scan with the same scanning parameters, depends solely on the interpolation algorithm. Table speed and scanner geometry (either single slice or dual slice) have no effect on the noise value. For the given table speed, as well as individual detector collimation (slice width) the dual-slice scan results in better longitudinal resolution (SSP) compared to a single-slice scan if the scan is obtained with nonoverlapping slices (pitch greater than 2). This is because the dual-slice scan obtains twice the number of nonoverlapped projections for the same length, which reduces the degradation of the slice profile by using more densely arranged projections (in the longitudinal direction) for the interpolation. In the dual-slice scanner the workable scan rate is extended up to pitch 4 compared to a pitch of 2 for the single-slice scanner. Therefore, the dual-slice spiral scanner is preferred in applications requiring an increased scan rate with comparative image quality.

Computer Simulation↗
PubMed1995

Photoacoustic ultrasound (PAUS)--reconstruction tomography.

The theoretical underpinnings of photoacoustic ultrasound (PAUS) reconstruction tomography are presented. A formal relationship between PAUS signals and the heterogeneous distribution of optical absorption within the object being investigated is developed. Based on this theory, a reconstruction approach, analogous to that used in x-ray computed tomography, is suggested. Initial experimental results suggest that this approach produces "reasonable" reconstructions for absorbers distributed within a narrow plane embedded within a highly scattering medium.

Acoustics↗
PubMed1995

Volume detection threshold: quantitative comparison of computed radiography and screen-film radiography in detection of pneumothoraces in an animal model that simulates the neonate.

PURPOSE: To quantitatively compare computed radiography (CR) and screen-film radiography (SFR) in the detection of pneumothorax in an animal model that simulates the neonate. MATERIALS AND METHODS: Three rabbits underwent placement of 5-F catheters in the right pleural space. Eight CR and eight SFR images were obtained. Volume-controlled pneumothorax was induced by incrementally injecting 4 cm3 of air (24 cm3 total) and four CR and four SFR images were obtained after each injection. Four radiologists blindly viewed the images twice (eight readings per image, 1,600 total observations). A dichotomous yes-no score for the presence of pneumothorax was used to calculate the volume detection threshold (VDT), defined as the air volume at which 50% of the pneumothoraces can be detected. The authors plotted the likelihood of a pneumothorax against the air volume by using the confidence indicator. RESULTS: Intraobserver VDT values for CR and SFR were not significantly different. CONCLUSION: CR is as accurate as SFR in the detection of pneumothorax in this quantitative animal model.

Animals↗
PubMed1994

Photoacoustic ultrasound.

Differential absorption has been detected and localized in three-dimensions by recording the photoacoustic pulses that were produced when short-duration (approximately 1 microsecond) pulses of electromagnetic energy were absorbed regionally within a turbid medium. These absorption sites were localized with a spatial resolution of approximately 6 mm within a 20 x 20 x 7.5-cm3 volume of 0.3% Liposyn solution, a highly scattering medium. A Xenon flashlamp, delivering a nominal 1 microsecond pulse of broadband light, was used to irradiate the Liposyn solution. Photoacoustic echoes were recorded with a focused, ultrasonic transducer, tuned to a nominal frequency of 0.5 MHz. The spatial resolution that was demonstrated is consistent with the expected ultrasonic properties of the transducer. Improved spatial resolution can be expected with shorter-duration radiation exposure and higher-frequency transducer designs. The technique is generalizable to any electromagnetic energy range (including long-wavelength microwaves) that penetrates the medium and produces differential, regional absorption of energy.

Acoustics↗
PubMed1994

Photoacoustic ultrasound: pulse production and detection of 0.5% Liposyn.

Theoretical predictions and experimental measurements of photoacoustic pulse production within a 0.5% solution of Liposyn, a highly scattering, optical propagation medium, are reported. A simple model for photoacoustic energetics is developed that predicts photoacoustic signal pressure as a function of depth within a turbid medium following surface irradiation from an infrared source. The model is valid for very short irradiation duration. The model predicts that the acoustic pressure produced at a distance r from the center of a small, highly absorbing sphere of radius R consists of two, opposite polarity pulses, one originating from the near and one from the far side of the sphere. The magnitude of these biphasic pulses is expected to be proportional to the energy fluence (E) incident on the surface of the sphere and to the ratio, R/r. Furthermore, the energy fluence (E) that reaches the sphere is roughly proportional to e-mu effZ, where mu eff is the effective attenuation coefficient of the turbid medium and Z is the depth of the embedded sphere below the irradiated surface. The variation of E with depth within the absorber and biphasic acoustic pulse production have been verified experimentally. Further experiments demonstrate that a small (3-mm diameter), highly absorbing sphere can be detected and localized at a depth of 37.5 mm within a 0.5% solution of Liposyn with a spatial resolution of 1 x 6 mm2, using a biologically safe level of infrared irradiation (lambda = 1064 nm) and a conventional ultrasound transducer (frequency = 2.25 MHz). These results suggest that photoacoustic ultrasound imaging may have application to biologic systems such as the human breast.

Acoustics↗
PubMed1994

Rabbit pneumothorax. Feasibility of an animal model to simulate neonatal pneumothorax.

RATIONALE AND OBJECTIVES: The feasibility of developing an animal model to simulate radiographic features of neonatal pneumothorax was investigated, and supine computed radiography (CR) and film-screen radiography (FS) images were compared. METHODS: 5-Fr pigtail catheters were inserted into the right pleural space of three New Zealand white rabbits. Two CR and two FS supine images were obtained using identical technique. After serial 4-mL injections of air, one CR and one FS supine image were obtained. The images were masked and randomized, and four radiologists reviewed the images for typical signs of pneumothorax. Chest computed tomography (CT) was performed before the injection of any air and after completion of the study. RESULTS: At zero-mL air volume, radiologists did not perceive a pneumothorax. As the air volume increased, the number of signs of a pneumothorax increased; there was no significant difference between CR and FS in the number of signs of pneumothorax detected at any volume. Chest CT confirmed that there was no unexplained air leak. The volume of air injected correlated with the calculated volume from the CT. CONCLUSIONS: This induced, volume-controlled, animal model simulated the supine radiographic features of neonatal pneumothorax.

Animals↗
PubMed1991

The problem of recurrent stenosis following carotid endarterectomy.

From 1977 to 1985, 306 consecutive patients underwent carotid endarterectomy by a single surgeon. The post-operative stroke and death rates were 1.3% and 2.6%. Of the 184 patients with follow-up duplex scanning, 24 (13%) had a recurrent stenosis of 50% or greater. Of 15 possible risk factors studied to assess a possible relationship with recurrent stenosis, four were definitely associated and a fifth probably implicated. The four definitely associated risk factors for recurrent stenosis were an age of 70 years or older (p = 0.0025), female gender (p = 0.0001), ulcerated lesions (p = 0.013), and asymptomatic lesions (p = 0.041). The fifth risk factor that may play a role (though not reaching statistical significance) was combined carotid endarterectomy and myocardial revascularization (p = 0.066). In these patients, we recommend using vein patch angioplasty to reduce the recurrence rate.

Aged↗
PubMed1990

Emergency eye injuries.

This study analyses all patients presenting with eye complaints to the casualty section of a Brisbane Hospital during a one month period. Eye complaints constituted 3.6 per cent of all patients. A foreign body was involved in 57 per cent of all eye injuries. The patients were subject to a trial assessing the effectiveness of antibiotic treatment following removal of the foreign body. There was no significant difference between antibiotic and placebo (sterile saline).

Corneal Injuries↗
PubMed1989

Comparison of dual-energy and conventional chest radiography for nodule detection.

This paper presents the results of a nodule detection study, using a Humanoid chest phantom, which was designed to evaluate the performance of two types of dual-energy and conventional (single-energy) chest radiography. The film-screen apparatis were used as image detectors for all imaging modalities. The area under the ROC curve and the cumulative true-positive fraction both were used as performance indexes in the evaluation. Because of the small number of false-positive responses in the observer studies, the cumulative true-positive fraction was eventually regarded as a more conclusive index of accuracy than the area under the ROC curve to make a reasonable conclusion. Both dual-energy techniques, dual- and single-exposure, were found to be superior to conventional chest radiography, P less than 0.0005 and P less than 0.006 for dual- and single-exposure techniques, respectively. The difference between the two dual-energy techniques was statistically insignificant, P less than 0.47. We concluded that the dual-energy, single-exposure technique is worthy of further clinical study based on these encouraging results and because of the ease with which the technique can be implemented.

Humans↗
PubMed1988

Medical imaging strategies.

Computed tomography (CT), intravenous digital subtraction angiography (IV-DSA), digital radiographic image processing and dual energy subtraction are four examples of medical imaging strategies that have met with various degrees of success as judged by diagnostic performance. The success of CT has been spectacular; IV-DSA has provided modest benefits; digital image processing of chest radiographs has been singularly disappointing; and the verdict on dual energy subtraction is undecided. The degree of success of each of these techniques can be understood by considering the degree to which each simplifies image interpretation or isolates a fingerprint of disease.

Angiography, Digital Subtraction↗
PubMed1988

An electrodeless measuring technique for determining conductivity of biological tissues at radio frequencies.

An electrodeless measuring technique for determining the conductivity of biological tissues at radio frequencies is described. The technique is based on measuring magnetic power dissipation in a conducting sample using a tuned circuit when the sample is immersed in a time-varying magnetic field. Theory regarding the measurements is presented. Consideration for coil design is given. Coil construction and measurement techniques are described in detail. The technique has three advantages: errors resulting from electrode lead inductance are completely removed; contacts between tissue surfaces and electrode surfaces are not needed; and maintaining water content and concentration of pH solution inside the tissues during measurements becomes easily facilitated. With the technique, conductivity values of dog kidney at room temperature were obtained in good agreement with previous work.

Animals↗
PubMed1988

Quantitative digital subtraction coronary angiography using videodensitometry. An in vivo analysis.

A videodensitometric method for measuring absolute cross-sectional area and diameter has been tested in living dogs with coronary artery stenoses created surgically by placement of small Silastic cuffs. Coronary arteriograms were performed using a circular tomographic unit to provide multiple views of each lesion, and measurements were made from logarithmically subtracted digital images. Dimensions of 13 stenoses of cross section 1 to 5 mm2 and adjacent reference segments (2 to 9 mm2) were determined by histologic sectioning of the segments after injection with a rapidly hardening plastic fixative under physiologic pressure. Two different methods were tested for calculating cross-sectional area. On 238 measurements, 102 of normal vessel segments and 135 of stenoses, both methods showed good correlation with histologic measurements, with slopes of 0.929 + (SD) 0.037 (r = 0.8563) and 0.948 + (SD) 0.037 (r = 0.8554). Multiple measurements of each segment produced values within 30% of the true absolute cross sectional area in most cases. The method shows promise as a means for quantitating absolute dimensions of vessels in clinical arteriography.

Absorptiometry, Photon↗