Biomedical subjects

J A Seibert

Publications and source records attributed to J A Seibert.

At least 37 records · Page 2Linked to original sources

PubMed1994

A comparison of mono- and poly-energetic x-ray beam performance for radiographic and fluoroscopic imaging.

The purpose of this investigation was to evaluate the potential of monoenergetic x-ray sources to improve image quality and reduce patient dose compared to conventional tungsten anode x-ray spectra. This was purely a computer simulation study. X-ray spectra were generated using the Birch and Marshal spectral model, patient x-ray transmission was calculated using Monte Carlo techniques, and a numerical method was developed for determining antiscatter grid performance. A 120 mg/cm2 Gd2O2S intensifying screen was simulated for radiography and a 144 mg/cm2 CsI image intensifier was simulated for fluoroscopy. The source of subject contrast that was simulated included tissue, calcium, and iodine targets which varied in mass thicknesses from 10 to 1000 mg/cm2. The figure of merit of the [contrast to noise ratio] 2/[integral dose] was used as a relative measure of dose utilization. Depending on the object thickness, monoenergetic x-ray sources with a screen-film detector exhibited a 1.4 to 2.4 improvement over tungsten anode spectra for iodine contrast, a 1.5 to 2.0 improvement for calcium imaging, and about a 1.4 to 1.6 improvement for tissue contrast. The thicker patients (30 cm) benefitted more than thinner (10 cm) ones. For the image intensifier as a detector, a 1.4-2.3 improvement factor was found for monoenergetic sources and an iodine signal object. For the practical range of radiographic imaging scenarios using present-day detector technologies, monoenergetic sources may provide an improvement in dose utilization that is comparable to the improvements that can be expected with scanning slit devices over conventional antiscatter grids.

Algorithms↗

PubMed1994

An analytical edge spread function model for computer fitting and subsequent calculation of the LSF and MTF.

The previous work of Yin, Giger, and Doi [Med. Phys. 17, 962-966 (1990)] demonstrated that using a computerized fit of an analytic line spread function to experimentally measured data is very useful for determining the presampling modulation transfer function of an imaging system. In this report, the work of Yin et al. is extended to include an analytic expression for the edge spread function (ESF). By fitting experimentally determined edge spread function data to the analytical expression, the normalized line spread function (LSF) and the normalized modulation transfer function (MTF) can be easily calculated from four ESF fit coefficients. The extension from the line spread function to the edge spread function should be valuable in cases where slit measurements are impractical, for example, in very high resolution imaging systems where the required slit dimensions become impractically small, or in measurements of the transfer properties of scattered radiation or off-focus radiation, where large area exposures are necessary.

Algorithms↗

PubMed1994

Medical physics.

Explore the source record for details and available documents.

Diagnosis, Computer-Assisted↗

PubMed1993

Bone marrow transplantation in dogs after radio-ablation with a new Ho-166 amino phosphonic acid bone-seeking agent (DOTMP).

beta-emitting 166Ho (t1/2 = 26.78 hours, E(beta)max = 1.8 MeV) complexed with the phosphonic acid chelator, 1,4,7,10 tetraazacyclododecane-1,4,7,10-tetra(methylene phosphonic acid) (DOTMP) at a ligand-to-metal ratio of 1.5:1 binds to bone. This radioactive complex is a marrow-ablating radiopharmaceutical that appears useful for preparation of bone marrow (BM) transplant recipients without the morbidity usually associated with total body irradiation preparatory regimens. We have found with seven splenectomized young adult beagle dogs that a 166Ho radiopharmaceutical dosage of 370 MBq/kg body weight provides an initial skeletal radioactivity burden of at least 1.5 GBq/kg skeleton and results in complete ablation of hematopoietic marrow cell populations within 7 days. The beta particle flux distribution in BM-forming skeletal tissue is not uniform. Red marrow radiation doses varied from 30 to 115 Gy as estimated by direct radioassay and autoradiographic analyses of both bone biopsies and postmortem samples; the median value of 61 Gy agreed with our theoretical expectations. In vivo radioactivity distribution was evaluated with nuclear imaging methods. Apparently, normal hematopoiesis was restored in three dogs with autologous BM transplants performed 5 to 6 days after administration of the marrow ablative radiopharmaceutical, 166Ho-DOTMP. BM biopsies at 7 to 10 months posttransplantation indicate continued normal hematopoietic activity.

Animals↗

PubMed1993

A fluoroscopy-based computed tomography scanner for small specimen research.

RATIONALE AND OBJECTIVES: A small-laboratory computed tomography (CT) system using a fluoroscopic system and a personal computer was fabricated and tested. The motivation for building this specimen scanner was to provide medical researchers with the capability of using CT as a practical tool in their research, as well as to provide an opportunity for hands-on CT instruction. METHODS AND MATERIALS: The CT system was constructed using mostly off-the-shelf items; however, the CT stage itself was custom fabricated and software development was necessary. In addition, a personal computer and a standard fluoroscopy system were used. RESULTS: The spatial resolution was found to match the 228-microns sampling limitation, yielding approximately 2 line pairs per mm. Iodine contrast sensitivity studies showed that 1% solution of 370 mg/ml iodine solution was easily detected (P = .05). CONCLUSIONS: A small CT scanner for specimen research can be economically constructed, and is capable of good performance. The authors found substantial interest on the part of small animal researchers involved in a wide variety of medical research.

Animals↗

PubMed1991

Differential effect of recombinant tissue plasminogen activator-induced thrombolysis in the central nervous system and systemic arteries.

Recombinant tissue plasminogen activator (rTPA) has been more effective in inducing thrombolysis in laboratory studies of intracranial thrombosis than clinical studies of systemic or coronary thrombosis would indicate. To evaluate this discrepancy, 21 rabbits were subjected to embolic occlusion of the right internal carotid artery (ICA) by retrograde injection of a tin-tagged, 2-hour-old autologous clot through the external carotid artery with angiographic monitoring in the same manner as in a previously reported model. The emboli lodged intracranially at the bifurcation of the ICA in 10 animals and in the cervical ICA in 11 animals. Digital subtraction angiography confirmed total occlusion of the ICA in all animals. Treatment started one-half hour after embolization and consisted of a bolus of 0.5 mg/kg of rTPA followed by an infusion of 1 mg/kg/h for 2 hours. All of the animals with intracranial emboli and 6 of the animals with cervical emboli were treated intravenously. The remaining 5 animals with cervical emboli were treated by intracarotid infusion of the same dose of rTPA. In the intravenously treated group, serial digital subtraction angiography documented thrombolysis in 9 of the 10 animals with intracranial emboli and only 1 of the 6 with cervical emboli. Thrombolysis occurred in 4 of the 5 rabbits with cervical emboli treated with intracarotid rTPA. Intravenous rTPA therapy produced a significantly (P less than 0.01) higher rate of thrombolysis in intracranial as compared to cervical thrombus.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1991

Orthogonal electrode catheter array for mapping of endocardial focal site of ventricular activation.

Precise location of the endocardial site of origin of ventricular tachycardia may facilitate surgical and catheter ablation of this arrhythmia. The endocardial catheter mapping technique can locate the site of ventricular tachycardia within 4-8 cm2 of the earliest site recorded by the catheter. This report describes an orthogonal electrode catheter array (OECA) for mapping and radiofrequency ablation (RFA) of endocardial focal site of origin of a plunge electrode paced model of ventricular activation in dogs. The OECA is an 8 F five pole catheter with four peripheral electrodes and one central electrode (total surface area 0.8 cm2. In eight mongrel dogs, mapping was performed by arbitrarily dividing the left ventricle (LV) into four segments. Each segment was mapped with OECA to find the earliest segment. Bipolar and unipolar electrograms were obtained. The plunge electrode (not visible on fluoroscopy) site was identified by the earliest wave front arrival times of -30 msec or earlier at two or more electrodes (unipolar electrograms) with reference to the earliest recorded surface ECG (I, AVF, and V1). Validation of the proximity of the five electrodes of the OECA to the plunge electrode was performed by digital radiography and RFA. Pathological examination was performed to document the proximity of the OECA to the plunge electrode and also for the width, depth, and microscopic changes of the ablation. To find the segment with the earliest LV activation a total of 10 +/- 3 (mean +/- SD) positions were mapped. Mean arrival times at the two earlier electrodes were -39 +/- 4 msec and -35 +/- 3 msec. Digital radiography showed the plunge electrode to be within the area covered by all five electrodes in all eight dogs. The plunge electrode was within 1 cm2 area of the region of RFA in all eight dogs. The width and depth of ablation were 5 +/- 3.5 and 7 +/- 3.5 mm, respectively. Microscopic changes revealed coagulative necrosis, hemorrhage, and inflammatory changes in all RFAs. In conclusion, the OECA can map the endocardial focal site of origin of paced ventricular activation within 1 cm2 area in a canine model. RFA from the OECA can cause discrete ablations representing all five electrodes or cross-shaped ablation connecting central electrode to all four peripheral electrodes. This catheter holds promise for extending surgical and clinical catheter ablation procedures.

Animals↗

PubMed1991

Exposure rates in high-level-control fluoroscopy for image enhancement.

High-level fluoroscopic boost options that exceed conventional exposure limits are available as a means of reducing quantum mottle during angiography. Federal law does not specify exposure limits for such high-level controls but requires specific means of activation to safeguard against inadvertent use. The American Association of Physicists in Medicine recently recommended that high-level exposure rates not exceed 2.58 mC/kg/min (10R/min). At six institution surveyed, maximum exposure rates ranged from 5.42 to 24 mC/kg/min (21-93 R/min). Activation of high-level capability varied from a simple foot switch to a keyed interlock requiring a second operator to engage. There appears to be no industry coherence in high-level control exposure limits as yet, although the Center for Devices and Radiological Health recently initiated an investigatory program.

Environmental Exposure↗

PubMed1989

Internal densitometric gating for digital subtraction angiography.

Motion artifacts create a severe problem in digital subtraction angiography (DSA) studies. Periodic motion can be eliminated by "gating," matching a precontrast mask with a postcontrast image at the same phase position in the cycle. Electrocardiogram (EKG) signals are used in cardiac DSA for this purpose. An alternate method relies on the generation of a density-time curve dependent on the attenuation changes of anatomical motion. A densitometric window placed at an appropriate location records the variation, from which individual images are tagged with phase position information encoded as delay time. Results are similar to the EKG gating method for cardiac DSA when using an appropriate window location. Periodic motion caused by superimposed respiration can be suppressed by tracking diaphragm or other object attenuation changes with the same algorithms. Using these techniques permits the nonarbitrary matching of mask and contrast images without physiologic monitoring. The techniques are straightforward and relatively easy to implement on systems designed for rapid digital imaging.

Angiography↗

PubMed1989

Partial splenic embolization guided by blood flow measurements.

The author used blood flow measurements to guide partial splenic embolization procedures in five patients. The measurements were obtained by time density analysis of contrast medium injections in the splenic artery using digital subtraction angiographic techniques and modified software. The blood flow measurements demonstrated blood flow changes occurring as a result of the embolization. The embolization procedures continued until the blood flow in the splenic artery had been reduced to 50% of its original value. The blood flow measurements appear to predict the amount of parenchymal reduction achieved by embolization and show promise as a method of monitoring these procedures.

Adult↗

PubMed1989

Evaluation of recombinant tissue plasminogen activator in embolic stroke.

In an effort to determine the value of tissue-type plasminogen activator (TPA) in the treatment of embolic stroke, 17 rabbits were subjected to a model of embolic stroke in which 2-hour-old, tin-impregnated, autologous clots were embolized to the bifurcation of the internal carotid artery at the circle of Willis via retrograde injection into the cannulated external carotid artery. High-resolution digital subtraction radiography was used to localize clots intracranially at the carotid bifurcation. Circulation through the internal carotid artery and intracranial vessels was monitored with serial digital subtraction angiography before and after embolization and during treatment. Disappearance of the tin marker on the digital subtraction radiograph indicated dissolution of clot and was associated with reestablishment of circulation on the digital subtraction angiogram. Experimental animals were treated with human-specific recombinant TPA 30 minutes, 2 hours, or 4 hours after clot embolization. TPA was administered as an intravenous bolus of 0.5 mg/kg followed by an infusion of 1 mg/kg/h for 2 hours. Digital subtraction angiograms were performed every 30 minutes. All clots dissolved, and cerebral circulation was reestablished within 120 minutes of treatment. In control animals treated with saline, embolized clots were stable, and the internal carotid artery remained occluded. At the completion of each study, the animal was perfused with freshly prepared, buffered 2,3,5-triphenyltetrazolium chloride (TTC) for demarcation of cerebral infarction. Control animals demonstrated infarction of 50 +/- 3.6% of the ipsilateral cerebral hemisphere, with an infarct weight of 2.1 +/- 0.2 g.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1988

Scattered energy deposition under shielding.

Monte Carlo methods are used to generate line spread functions describing dose distributions at a variety of depths within a homogeneous water phantom. The line spread function data are convolved with a step function that represents the edge of a primary radiation field. The dosimetric information beyond the edge of the field is reported in the form of tissue-air ratios for three different beam spectra in the diagnostic energy range.

Models, Structural↗

PubMed1987

Digital angiographic quantification of blood flow dynamics in embolic stroke treated with tissue-type plasminogen activator.

Computer analysis of digital subtraction angiography (DSA) was utilized to quantify the effectiveness of tissue-type plasminogen activator (TPA) in a rabbit cerebroembolic stroke model. Fourteen animals underwent cannulation of the facial artery and a preembolus angiogram. Autologous blood clots were then injected, and occlusion of the internal carotid artery at the circle of Willis was documented with repeat angiogram. The experimental group received a 1-mg/kg intravenous infusion of TPA via a femoral catheter for 90 minutes. A control group received an equivalent volume of saline. Follow-up angiograms were performed every 15 minutes. The TPA-treated animals showed progressive improvement in flow through previously occluded vessels. Time-density curves of the contrast material over the middle cerebral artery trunk and brain parenchyma were generated. The best integrated curves for the two groups were compared at 30 minutes after occlusion and 90 minutes after treatment. Animals were then observed for 24 hours and their neurological status was documented. Premortem infusion of either Evans blue dye or neutral red dye was performed and the integrity of the blood-brain barrier and tissue perfusion were assessed by video planometry. Significant improvements were noted by DSA, and Evans blue and neutral red dye studies in animals treated with TPA.

Animals↗

PubMed1986

Improved fluoroscopic and cine-radiographic display with pulsed exposures and progressive TV scanning.

In fluoroscopic image display, moving objects lose resolution because of continuous x-ray exposure and interlaced TV scanning. Significant improvements can be obtained with progressive TV scanning synchronized to short x-ray pulses occurring at a rate of 30 Hz. Modification of the x-ray generator and addition of a progressive-scan TV camera coupled with a scan converter (progressive to interlaced) allows one to maintain fluoroscopy radiation levels, prevent image refresh flicker, and use existing low bandwidth interlaced monitors for optimum image quality.

Animals↗

PubMed1985

Videodensitometric quantitation of stenosis: in vitro and in vivo validation.

Percentage of stenosis of a vascular lumen was quantitated using a digital subtraction angiography system with videodensitometric analysis. To validate the algorithm and methods, we used precisely drilled Lucite rods of three inner diameters and various reduced diameters to give known luminal reduction. Both in vitro and in vivo results of stenosis measurements resulted in an excellent correlation between actual and measured values (correlation coefficient greater than 0.9 for all trials). Consistent underestimation of stenosis of about 5% was attributed to the various image degradations inherent with the imaging procedure and equipment. Errors were greatest with midrange stenoses and less at the extremes of the lesion values. An insufficient signal-to-noise ratio was caused by low photon flux and/or low contrast material concentration and overlying vasculature filled with contrast material. Overall, the videodensitometric technique is accurate, easy to implement, objective, and relatively free of errors associated with the geometric/edge detection method.

Absorptiometry, Photon↗

PubMed1984

On the relationship of image intensifier contrast ratios measured by two techniques.

In recent years the contrast ratio (CR) has played an important role in the quantitation of imaging performance of X-ray image intensifiers. In practice, one uses either a lead disc or strip for measurement of contrast ratios. A theoretical relationship relating contrast ratios measured by both disc and strip techniques is discussed and experimental results are presented. The theoretical analysis uses the point spread function model to describe veiling glare for an image intensifier. It has been shown that one can predict strip contrast ratios after a determination of the veiling glare point spread function from a measurement of disc contrast ratios.

Methods↗

PubMedDate not supplied

The beneficial effects of short pulse width acquisition and ECG-gating in digital angiocardiography.

Experimental intravenous left ventriculography and coronary angiography after aortic root injection were performed in 13 animals. Various image acquisition and digital image processing techniques were employed. These included single mask mode subtraction, integrated mask mode subtraction, ECG-gated image acquisition, TV camera read-out in interlaced mode, and pulse progressive read-out with 1- to 5-ms pulse width. High quality images were obtained consistently only after ECG-gating and use of 1- to 5-ms pulse width with pulse progressive read-out of the TV camera. Integration of four to eight background as well as contrast images all from the same phase of the cardiac cycle further improved image quality.

Angiocardiography↗

PubMedDate not supplied

Quantitative methods for indirect CT lymphography.

In this investigation, we applied quantitative CT methods to characterize contrast enhanced lymph nodes opacified using iodinated contrast media for indirect CT lymphography. Iodinated nanoparticles were injected into the buccal submucosa and SQ into the metatarsus and metacarpus of four normal swine (1.0-4.0 ml/site, 76 mg I/ml). Attenuation (HU), volume (cm3), iodine concentration (mg I/cm3), total iodine uptake (mg I), contrast-to-noise ratio (CNR), and percent injected dose (%ID) were estimated in opacified inguinal, cervical and parotid/mandibular lymph nodes using manual image segmentation techniques on 24 hour post-contrast CT images. Lymph node volumes estimated by multiple slice ROI analysis were compared with estimates obtained by post-excisional weight measurements. HU and iodine concentration increased 5-20 fold in opacified nodes (p < 0.01) and CNR increased more than four-fold (p < 0.001). %ID ranged between 3.5 and 11.9% and did not appear dose related. ROI estimated lymph node volumes approximated volumes calculated from weight measurements. (R2 = 0.94, p < 0.0001). We conclude that interstitially injected iodinated nanoparticles increase attenuation and conspicuity of targeted nodes on CT images. Quantitative methods could play an important clinical role in more accurate metastasis detection.

Animals↗