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PubMed1994

[Superimposition of MR angiography and three dimensional radionuclide brain perfusion image with personal computer].

To investigate the correlation of arterial obstruction with brain perfusion, MR angiography (MRA) and three dimensional (3D) radionuclide brain perfusion image were superimposed. Eleven cases with intracranial artery obstructive patients were studied. Three dimensional brain perfusion images were generated based on the ray-tracing method. Superimposition of MRA on to 3D brain perfusion image was performed on a personal computer. Reconstructing time for 3D image was about 15 minutes for each patient, Superimposing time was about 5 minutes for each image. Correlation of arterial obstruction with decrease in brain perfusion was demonstrated clearly by superimposed image. With a personal computer, it was possible to produce clinically useful synthesized images with relatively short time and conveniently.

Adult↗
PubMed1994

[Value of 3-dimensional emission scintigraphy in evaluating the osseointegration properties of endoprostheses].

The Three-dimensional display of functional images generated by single photon emission computed tomography gives a three-dimensional picture of the bone and the activity of a radionuclide after endoprosthetic joint replacement and allows a judgement of osteoblastic activity concerning bone ingrowth in macroporous surfaces of non-cemented implants. Osteolytic processes can be demonstrated in the same way.

Computer Graphics↗
PubMed1986

Cortex perfusion index: a sensitive detector of acute rejection crisis in transplanted kidneys.

Damage to the renal cortical microcirculation, an early event in the course of acute rejection crisis (ARC), usually precedes measurable functional derangements in the transplanted kidney. Direct assessment of cortical blood flow by radionuclide renography may provide a sensitive and reliable index to the diagnosis of ARC, with particular regard to the differential diagnosis of ARC and ATN. Computer generated time-activity curves of global, cortical, and medullary renal blood flow were analyzed in 67 instances (35 patients) of renal allograft dysfunction and correlated with needle biopsy of these kidneys. No increase in cortex perfusion index (CPI), i.e., decrease in cortical perfusion, was found when the patients were suffering from ureteral obstruction or drug and viral nephropathy (mean perfusion index (PI) increase (8%). In contrast, a marked increase in CPI of 193% was noted in ARC. Global and medullary PI increased only 116%. As a result, global and medullary PI were capable of diagnosing ARC in only 73% and 55% of the cases, respectively, whereby cortex PI correctly diagnosed ARC in 94% of the cases. Selective analysis of cortical perfusion may thus enhance the accuracy of [99mTc]DTPA scans (radionuclide renograph) for the early detection of ARC and in differentiating ARC from nonimmunological causes of kidney allograft dysfunction.

Graft Rejection↗
PubMed2002

In vivo molecular imaging.

The relatively young field of molecular imaging is focused on the visualization of molecular phenotypes in whole organisms. This is achieved using imaging systems based on radionuclides, nuclear magnetic resonance, ultrasound, or the visible-IR region of the optical spectrum. Molecularly defined contrast in these modalities is generated by exogenous probes of the endogenous proteome, or through transgenes. Examples of exogenous probes include those that are transported and trapped (glucose, nucleoside analogs), those directed against extracellular receptors (somatostatin, opioid, melanotropin), and those activated by extracellular proteases. Transgenes that have been used in molecular imaging include the above receptors, non-mammalian enzymes that trap pro-drugs (HSV-tk, yeast CD), and optical reporter proteins (luciferase, fluorescent proteins). Cutting edge technologies in this field include in vivo assays for protein-protein interactions, and in vivo assays for mRNA expression patterns. The number of degrees of freedom in designing new agents is daunting, and advancements in this field will require a significant participation from molecular and cellular biochemists.

Animals↗
PubMed1991

Performance of a single crystal digital gamma camera for first pass cardiac studies.

First pass radionuclide angiocardiography (FPRNA) has gained increasing interest because of the development of new 99Tcm-labelled perfusion agents and of new 191Os/191Irm generator systems. The aim of the study was to evaluate the performance capacities of a small field of view single crystal digital gamma camera for 99Tcm and 191Irm at high count rates. The camera dead time for 99Tcm (window 30%) was well corrected up to 300 kcps in fast acquisition mode using the relative decrease of a small shielded reference source. Using the decaying activity method for 191Irm the non-linearity response of the gamma camera was corrected by an 191Os reference soruce up to 210 kcps at 70 keV, 75 kcps at 129 keV and 320 kcps including both peaks. Saturation count rates were respectively 270 kcps, 150 kcps and 420 kcps and high count rate resolution (FWHM) 9.0, 7.3 and 10.3 mm. Since the accuracy of first pass measurements is more sensitive to count rate than to spatial resolution the 50-150 keV window was chosen for clinical studies. In data obtained from 32 ECG gated FPRNA patient studies, the whole field of view count rate during the left ventricular phase ranged from 100 to 250 kcps with 80 to 120 mCi (2960-4400 MBq) of 191Irm and 100 to 180 kcps with 20 to 25 mCi (750-925 MBq) of 99Tcm red blood cells permitting for both tracers accurate non-linearity correction.

Evaluation Studies as Topic↗
PubMedDate not supplied

Intravenous 99mTc HM-PAO radionuclide angiography as an adjunct to SPECT assessment of cerebral disease.

An application of intravenous radionuclide angiography as an adjunct to SPECT with 99mTc HM-PAO is presented. From the angiographic sequence a two-dimensional parametric image is generated computing, pixel by pixel, the center of gravity (COG) of the local time curves. This index is independent of blood flow and reflects the relation between transmitted and extravasated activity. COG value, compared in two symmetrical regions analyzed for differences in flow by SPECT, may help to state whether a detected SPECT changed uptake is linearly related or not to the corresponding change of blood flow. All 23 ischemic patients taken into consideration had a similar backflux in symmetrical regions with conspicuous changed uptake. In 3 meningiomas and 2 arteriovenous angiomas it was possible to detect the occurrence of a changed backflux in the lesion suggesting a nonlinearity between blood flow and 99mTc HM-PAO uptake.

Brain Ischemia↗
PubMed2006

Effective dose scaling factors for use with uranium series cascade impactor data: a reassessment using the IMBA code.

Air sampling with a multi-stage cascade impactor enables one to assess airborne radioactivity as a function of particle size, significantly enhancing the accuracy of the dose assessment. The application of cascade sampling data to inhalation dose assessments can require more computational effort if something other than a mono-sized distribution per impactor stage is to be considered. To overcome this limitation, Kim et al. (Health Phys 89:359-374; 2005) introduced the concept of an effective dose scaling factor SF(E) enabling one to consider more realistic impactor stage radioactivity distributions (uniform, linearly decreasing, or linearly increasing variations with particle size). The SF(E) is the ratio of the effective dose given under a uniform or linearly changing radioactivity distribution across the particle size interval to that given for a mono-sized radioactivity distribution for the same impactor stage. The latter approach can initially be used (which requires less computational effort) followed by a rescaling of the effective dose either upward or downward by the SF(E) value. In this earlier study, the LUDEP code was employed which utilizes the ICRP 66 human respiratory tract model along the radionuclide biokinetic models given in ICRP Publication 30. In the present study, inhalation dose coefficients and effective dose scaling factors were reexamined for several radionuclides of the (238)U series using the IMBA program, which employs more recent and physiologically realistic biokinetic models published by the ICRP. An update of the effective dose scaling factors is thus the primary focus of this study rather than an extensive inter-comparison of the IMBA and LUDEP codes. Inhalation dose coefficients calculated by the two programs differ by up to a factor of 5 for Type F (238)U and (234)U, but are within only 2% of each other for Type S radionuclides. The ICRP 69 biokinetic model of uranium predicts retention in bone and kidneys that is slightly higher than predicted in ICRP Publication 30, but is significantly higher in the liver and other soft tissues by up to 1 or 2 orders of magnitude. Nevertheless, effective dose scaling factors generated using the IMBA program are nearly identical to those calculated by the LUDEP program as their magnitude is primarily dictated by the dependence of particle deposition and lung clearance with particle size, and less by the systemic biodistribution of the radionuclide following absorption to blood. For both codes, greater than 10% re-scaling of the effective dose is required for third-stage (4.5 to 12 microm) and filter-stage (0.03 to 0.35 microm) particles in the approximation of uniform or linearly decreasing radioactivity distributions per particle stage. For linearly increasing distributions, greater than 10% corrections in the effective dose are found irregularly across impactor stage, radionuclide, and solubility class, especially for rather steep (1:5) impactor stage activity ratios.

Air Pollutants, Radioactive↗
PubMed1984

An assessment of health risk from radiation exposures.

A methodology has been developed to assess potential hazards from low-level exposures to radioactive pollutants. Estimates of dose rates to reference organs from internal and external exposure pathways (inhalation of contaminated air, ingestion of contaminated food or water, immersion in contaminated air, and exposure to contaminated ground surfaces) are computed with contemporary dosimetric models. These dose rates are used in a life-table analysis to estimate the radiation-induced cancer deaths and resultant years of life lost in an exposed cohort of 100,000 persons, all simultaneously liveborn and subject to the same risks of dying from competing causes (including natural background radiation). Estimates of the potential health risk are tabulated for approx. 150 radionuclides for each of the exposure pathways; results are summarized in terms of the probability of premature radiation-induced death for a member of the cohort due to incremental radiation exposure, and the average number of years of life lost per incremental fatality. The estimates of radiation-induced mortality generated by these methods provide a useful means of quantifying radiation risk; however, these estimates may be subject to large uncertainties, and can be best interpreted as a measure of the relative degree of hazard associated with exposures to various radionuclides through several exposure pathways.

Actuarial Analysis↗
PubMed1979

Validity of left-ventricular ejection fractions measured at rest and peak exercise by equilibrium radionuclide angiography using short acquisition times.

To validate ejection fraction (EF) calculations from 5 and 2 minutes of multiple-gated equilibrium radionuclide angiographic data and to establish its utility during alterations in cardiac performance, we studied 38 patients with chest pain suggestive of coronary artery disease. Twenty-four patients underwent contrast ventriculography (CV) as well as first-pass (FP) and equilibrium (EQ) radionuclide angiography at rest, and 14 additional patients had both radionuclide tests performed at rest as well as during peak supine bicycle exercise. The resting 5-min acquisition ejection fractions were compared between each method and the following correlations were generated: r = .92, n = 24 (CV-EQ), r = .92, n = 24 (CV-FP), and r = .95, n = 38 (FP-EQ). The variability of EQ-EF calculations between two independent observers was less than 2%; the mean absolute difference between two sequential 2-min acquisitions and the 5-min recordings was -.1 +/- 1.6%, and the reproducibility of sequential 2-min ejection fractions was excellent (r = .98). EQ and FP ejection fractions at symptom-limited exercise correlated well (r = .96, n = 14). We conclude that equilibrium radionuclide angiography is a valid method to measure EF both at rest as well as during peak exercise even when 2-min acquisition periods are used.

Adult↗
PubMed1991

An improved radionuclide technique for the detection of altered pulmonary permeability.

Technegas, an ultra-fine dry aerosol with prolonged retention in the lungs, can be modified by altering the atmosphere in which the carbon particles are generated. The modified Technegas has much faster clearance from the lung. The half-time pulmonary clearances with modified Technegas were compared to those obtained with conventional 99mTc DTPA aerosol in 50 patients. Interstitial lung disease was suspected in 12 while 38 were infected with the human immunodeficiency virus and suspected of having opportunistic lung infection. In 22 nonsmokers in whom no evidence of active pulmonary pathology was demonstrable, the mean half-time with DTPA was 52.5 min whereas the mean half-time with modified aerosol was 10.1 min. The mean half-time in 14 smokers in whom there was also no evidence of active pulmonary disease was 28.3 min with DTPA and 7.0 min with the modified method. In the 14 patients in whom altered pulmonary permeability was demonstrated by a short DTPA half-time (mean 4.8 min) there was also an accelerated half-time with modified Technegas (mean 2.5 min). It is concluded that the modified Technegas procedure offers a simple but accurate method of identifying individuals having opportunistic infection or other diffuse lung pathology.

Acquired Immunodeficiency Syndrome↗
PubMed1981

Computer processing of perfusion, ventilation, and V/Q images to highlight pulmonary embolism.

A method is described for generating regional ventilation/perfusion (V/Q) images of the lung to aid assessment of suspected pulmonary embolism, especially in patients with obstructive airways disease. The radionuclide scans used for this are stored on a computer and comprise; lung perfusion (P) with Tc-99 m MAA, lung ventilation at equilibrium (E) with Xe-127, and the sum of the Xe-127 washout images (W). A functional ventilation image is calculated as V=E/W and a functional perfusion image as Q=P/E. Finally a ventilation perfusion ratio image is obtained by taking V/Q. This is normalised by a factor determined from the cumulative frequency distributions of the counts per pixel in the Q and V images so that areas which are well ventilated and perfused are given a V/Q value of 1.10. Areas with normalised V/Q values greater than 1.5 suggest pulmonary embolism. In 100 studies on patients with pulmonary embolism. In 100 studies on patients with abnormal perfusion scans this method proved very helpful by assisting the recognition or exclusion of areas with abnormally high V/Q values.

Adult↗
PubMed1991

Interpreting results of exercise studies after acute myocardial infarction altered by thrombolytic therapy, coronary angioplasty or bypass.

Numerous studies have assessed the ability of exercise modalities to predict patient outcome after acute myocardial infarction (AMI). Implicit in the use of these prior data to assess the prognosis of patients currently undergoing exercise studies is the assumption that patients selected for exercise assessment are similar over time and that the data generated in the past are therefore applicable to the current patient populations. This study retrospectively assessed the clinical, exercise, and rest and exercise radionuclide angiographic data in 791 consecutive patients referred for exercise radionuclide angiography within 1 month after AMI during a 5-year period to determine if the clinical and exercise characteristics of patients referred for exercise evaluation after infarction have changed significantly over time. Most parameters examined demonstrated significant increasing trends, including thrombolytic therapy at the time of AMI, revascularization procedure between AMI and exercise assessment, age, beta-blocker usage, Q-wave AMI, inferior infarction, exercise double product, exercise capacity, significant ST-segment depression with exercise, peak ejection fraction, and change in ejection fraction with exercise. These data indicate that the characteristics of patients selected to undergo exercise after AMI in a large referral center have changed significantly over time. If these data are applicable to other referral centers and to other exercise testing modalities, previously published results regarding exercise assessment after AMI will need to be reconfirmed in patients currently selected for testing, since these results may no longer be applicable in this current era of aggressive medical and interventional management.

Angioplasty, Balloon, Coronary↗
PubMedDate not supplied

Marching cube algorithm: review and trilinear interpolation adaptation for image-based dosimetric models.

Current internal organ dose assessment methodologies utilize three-dimensional (3D) medical images of the body to model organ shapes and tissue interfaces. These models are coupled to computer programs that measure radionuclide energy deposition or chord-length distributions directly within these images. Previous studies have shown that the rectangular shape of image voxels generates voxel effects that alter the outcome of these calculations. To minimize voxel effects, the present study proposes to use the Marching Cube (MC) algorithm to generate isosurfaces delineating tissue interfaces from the gray-level images. First, a review of the different techniques surrounding the MC algorithm is presented. Next, an adaptation of the algorithm is proposed in which a trilinear interpolation of the gray levels is used to generate a hyperboloid surface within the MCs. This new technique is shown to solve the classic ambiguity problem of the MC algorithm and also to reduce the data size inherent to the triangulated surface. It also provides a simple algorithm to accurately measure distances within the image. The technique is then tested with a mathematical model of trabecular bone. The trilinear interpolation method is shown to remove voxel effects and to produce reliable chord-length distributions across image regions. The technique is thus recommended for use with digital medical images needed for internal radiation transport simulations. The current study is performed for a single isosurface that separates two media within the same image, but it is proposed that the technique can be extended to multiple isosurfaces that delineate several organs or organ regions within 3D tomographic voxels of human anatomy.

Algorithms↗
PubMed1984

Prognosis after myocardial infarction.

There is 10-20 percent mortality in the first two years after hospital discharge from a myocardial infarction. Patient management would be facilitated if one could stratify patients into those who have a low, medium or high risk of death within the first two years following infarction. Towards achieving this end a multicenter study was designed. 866 patients were enrolled over a two-year period from four widely separated geographic centers in the United States. Criteria for enrollment included definite acute myocardial infarction and age less than 70 years. 452 clinical variables were obtained from each patient and entered into a central computer file. Special studies obtained just prior to discharge included a 24-hour computer analyzed Holter recording and a radionuclide ejection fraction. 70 percent of the patients had a low-level predischarge treadmill activity test. Before the study a hypothesis was generated and tested prospectively. This was as follows: there are three clinical risk variables that have independent influence on survival. They are: ejection fraction less than 40 percent, ventricular ectopic depolarization frequency greater than 10 per hour, and the presence of angina pectoris before hospital discharge. The 22-month mortality was 11.6 percent (101 deaths). The variables which had the most significant association with cardiac mortality were those which reflected mechanical cardiac dysfunction either before or during acute hospitalization. The arrhythmia variable (VEDs) were less strongly associated with mortality than the mechanical parameters and the ischemia variable (angina pectoris prior to discharge) did not significantly discriminate between those who survived and died.(ABSTRACT TRUNCATED AT 250 WORDS)

Aged↗
PubMed1989

Effect of the second-generation calcium channel blocking drug nisoldipine on diastolic left ventricular dysfunction in heart failure.

The effect of intravenous nisoldipine (0.12 microgram/kg/min) on diastolic left ventricular (LV) dysfunction was studied from simultaneous hemodynamic and radionuclide measurements in 12 patients with New York Heart Association class II to IV cardiac failure. The initial LV filling fraction was low, the peak LV filling rate normalized for end-diastolic volume was decreased, and the pulmonary capillary wedge pressure (PCWP) was high and associated with clinical shortness of breath. Nisoldipine produced an increase in LV filling fraction from 36 +/- 17% to 43 +/- 20% (p = 0.003). The increase in filling took place in both early and late diastole: peak early filling rate (PFR) increased in 11 of the 12 patients (p = 0.02) and late diastolic filling rate (atrial [A] wave in eight of them (NS). When the determinants of these changes, were examined further, it was found that in the control state PFR was inversely related to LV end-systolic volume (r = 0.77), whereas the A wave was related in exponential fashion to PCWP (preload) (r = 0.79). Nisoldipine did not change the slope of these relationships, and it did not alter the end-diastolic pressure-volume relationship, implying that inherent myocardial relaxation and distensibility were unaltered by the drug. In summary, nisoldipine improved measurements of diastolic LV dysfunction in patients with cardiac failure. This study illustrates the importance of considering ventricular loading conditions when analyzing and interpreting measurements of diastolic ventricular dysfunction. The measured changes in diastolic LV function during infusion of nisoldipine appear to be due to alterations in ventricular loading conditions rather than to a direct myocardial effect of the drug.

Aged↗
PubMed1978

Dynamic radioisotope study of the internal carotid region of the neck in cerebrovascular disease.

The results of radionuclide angioscintigraphy were evaluated in patients with stricture or occlusion of the extracranial part of the internal carotid artery. Time-activity curves for the first 13 s were generated from left and right internal carotid regions of interest of the neck. The differences between the counts from symmetric regions of interest were measured. We observed decreased activity in regions of interest in cases with stricture of the internal carotid. The first 13 s were significant for evaluation of the extracranial part of the internal carotid.

Arterial Occlusive Diseases↗
PubMed2001

Effect of stent on radiation dosimetry in an in-stent restenosis model.

Purpose: Intravascular brachytherapy is the leading modality being evaluated for treatment of in-stent restenosis. Stent struts may have an effect on the dose distributions of various radiation sources. We evaluated dosimetry in a stented coronary artery model using a variety of beta and gamma sources and stent materials.Methods: We determined the dose distributions with and without stent in the in-stent restenosis model. Three beta-particle emitting radionuclides, 90Y (2.3 MeV), 144Pr (3.0 MeV), and 106Rh (3.5 MeV), and two gamma-ray emitters, 192Ir (380 keV) and 125I (30 keV), were studied. Stent materials included stainless steel, nitinol, and tantalum. Monte Carlo dose calculations were performed in a stent model of multiple stent struts placed at 1.5 mm from the source. Isodose curves were generated and the ratios of dose rates with and without stent, the stent factors, were evaluated. A stent factor of greater or less than unity represents dose enhancement or reduction in the presence of a stent.Results: For the three beta radionuclides, dose reduction was found on the adventitial side of the stent strut and dose enhancement was noted on the luminal side. On the luminal side, the maximum dose enhancement ranges from 7% to 29%, and the dose reduction on the adventitial side ranges from 13% to 43%. Both the reduction and enhancement effects were most pronounced for the high atomic number material, tantalum. For a given stent material, the dose reduction and enhancement are similar for the three beta radionuclides. For the gamma sources, the stent had no effect for the high-energy 192Ir, but for the low-energy 125I, drastic dose reduction on the adventitial side was observed (up to 86% for tantalum stent), and about 10% dose enhancement on the luminal side was also noted. The dose reduction with 125I was more pronounced than that seen with the beta sources.Conclusions: The presence of stent struts significantly affects dose distributions of 90Y, 106Rh, 144Pr, and 125I. The maximum dose reduction can be as much as 86%. 192Ir was unaffected. These factors need to be considered in choosing radionuclides and dose prescriptions in treating in-stent restenosis.

Journal Article↗