Hot Spot Imaging Research Articles

High-Resolution Millimeter and Infrared Observations of the Hot Spots of Cygnus A

We present high-resolution, polarimetric imaging of the radio hot spots of Cygnus A at 7 mm with the Very Large Array and derive limits to hot spot emission at 12 μm with the Infrared Space Observatory (ISO). The 7 mm images reveal the hot spot structure in total and polarized intensity in unprecedented detail, including images of the projected magnetic field morphology and the spectral index distribution between 7 mm and 3.6 cm at 025 resolution. The magnetic field distribution is consistent with Laing cells, involving a frozen-in field plus simple kinematic dynamo effects due to bulk fluid motions. The spectral index distribution suggests that distributed particle acceleration occurs in the hot spots. The ISO limits at 12 μm require an exponential cutoff in the hot spot spectra at ≈1013 Hz. Such a cutoff is predicted by standard shock acceleration theory for relativistic electrons. The exponential cutoff observed by ISO and the high-resolution images at 7 mm are used to set a lower limit to the streaming velocity of the relativistic electrons, of 0.4c. We also find that the nuclear spectrum of Cygnus A has a peak flux density at about 30 GHz. The origin of this peak is likely to be synchrotron self-absorption in the dominant nuclear component, implying a size of 0.15 mas (= 0.15 pc), with a magnetic field strength of 0.16 G and a pressure in relativistic particles and fields of 10-3 dyn cm-2. The nuclear flux density is 1.6 ± 0.16 Jy at 7 mm, and the nucleus was not seen to vary on a timescale of 1.3 yr to ≤10%. We also have possible detections at 12 μm of three of the galaxies in the Cygnus A cluster within ±3' of Cygnus A.

Optical Polarization and Imaging of Hot Spots in Radio Galaxies

We present subarcsecond optical imaging and polarization observations of five optical hot spot candidates in the classical double radio sources 3C 111, 3C 303, 3C 351, 3C 390.3, and PKS 2135-147. On the basis of positional coincidence, optical appearance, and polarization, all four 3C sources appear to have genuine optical counterparts to radio hot spots, whereas in PKS 2135-147 the hot spot candidate turns out to be an unrelated field galaxy. We also confirm the first ever optical double hot spot in the source 3C 351.

Failure analysis of integrated devices by scanning thermal microscopy (SThM)

High power densities dissipated in smaller and faster devices are leading to major thermal problems of semiconductor devices. The resulting local heat dissipation can induce deleterious effects like accelerated degradation or the destruction of the integrated circuits. Due to the shrinking feature sizes of modern devices and the small local extension of electrical failures the exact localization of these defects using established thermal failure analysis techniques like infrared thermometry becoming more and more difficult. Temperature measurements on passivated electronic devices with a sensitivity of 5 millikelvin by the use of a scanning thermal microscope (SThM) in contrast demonstrate the possibilities to use this system as a tool for failure analysis. Hot spot imaging with a spatial resolution of less than 150 nm, investigations on the backside of ULSI devices as well as a comparison with complementary established analysis techniques are presented.

Three-dimensional cold spot volume rendering

Three-dimensional volume rendering enhances the perception of radiopharmaceutical distribution within organs. Formerly, a maximum activity projection method was developed for hot spot rendering, which increases the contrast between hot spots and normal tissue. This method can only render cold spots at organ edges; a decrease in uptake within organs is not displayed. In this contribution, it is shown that the projection technique developed for hot spot imaging also can be used for cold spot rendering after suitable transformation of the tomographic data format.

Monte Carlo modelling of the performance of a rotating slit-collimator for improved planar gamma-camera imaging

The authors propose a rotating slit-collimator which collects one-dimensional projections from which the planar image may be reconstructed by the theory of computed tomography. The performance of such a collimator is modelled by Monte Carlo methods and images are reconstructed by a convolution and backprojection technique. The performance is compared with that of a conventional parallel-hole collimator and it is shown that higher spatial resolution with increased sensitivity is possible with the slit-collimator. For a point source a spatial resolution of some 6 mm at a distance of 100 mm from the collimator with a *7 sensitivity compared with a parallel-hole collimator was achieved. Applications to bone scintigraphy are modelled and an improved performance in hot-spot imaging is demonstrated. The expected performance in cold-spot imaging is analytically investigated. The slit-collimator is not expected to improve cold-spot imaging. Practical design considerations are discussed.

Global high-resolution imaging of hotspots on Io

We present 3.8 μm images of the Jovian satellite Io at an unprecedented ground-based resolution of 0″.18. The images were obtained through two-dimensional speckle interferometry using the 6.86 m aperture of the Multiple Mirror Telescope in November 1989 and March 1990. To process the images we developed new speckle reduction techniques appropriate for objects with a size that is a significant fraction of the field of view. The images show three volcanic hotspots, including Pele, detected here for the first time since the Voyager 1 flyby in 1979

Dual collimation acquisition for high resolution, low noise SPECT

Dual-collimation (DC) imaging for single photon emission computed tomography (SPECT) is presented as a technique to improve effective sensitivity with little loss of resolution. For some imaging tasks, DC can overcome the inherent tradeoff between resolution and sensitivity of gamma camera collimators. Simulations were used to investigate the system performance without the expense of collimator fabrication. With DC for SPECT, a single image which is consistent with two projection sets acquired in two different collimators is reconstructed, one with high resolution/low sensitivity and another with high sensitivity/low resolution. By incorporating a detailed model of the SPECT acquisition geometry (including each collimator) into the maximum-likelihood expectation maximization reconstruction algorithm, an image having a combination of moderate noise and moderate resolution is produced. Based on a preliminary evaluation of DC for SPECT, it is concluded that, for moderate-size (2-cm radius) cold lesion imaging, DC can provide significant improvement in contrast-to-noise without significantly sacrificing image contrast, although for smaller lesions this advantage is diminished. For small hot spot imaging, DC can provide significant improvement in image noise without significantly sacrificing image resolution. >

Imaging Necrotic Myocardium: Detection with99mTc-Pyrophosphate and Radiolabeled Antimyosin

The major value of hot-spot imaging of the myocardium is its ability to define areas of necrosis rather than areas of diminished blood flow or cellular function. Applications of hot-spot imaging include the diagnosis and quantitation of myocardial infarction, myocarditis, and cardiac transplant rejection. The two agents in clinical use, 99mTc-Pyrophosphate and radiolabeled antimyosin, are discussed.

On the imaging of hot spots using correlation radiometers and a circular aperture

Results of computer simulations are presented for a microwave correlation radiometer system that uses a circular synthetic aperture for imaging hot spots in homogeneous lossy tissue. The previously described system (see IEEE MTT-5 Int. Microwave Symp. Dig., p.155-6, 1988) combined with a reconstruction algorithm has the ability to reconstruct correctly the position and the power density ratios of point-shaped noise sources with spatial resolution that is nearly constant in all directions and all over the object plane. It is shown that inexactly known attenuation and phase constants of the tissue affect the reconstructions only slightly.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Two-dimensional imaging of hotspots in superconducting bridges by low-temperature scanning electron microscopy

Hotspots generated in a thin-film superconductor through dissipation of Joule energy are imaged by scanning the sample with the electron beam of a scanning electron microscope equipped with a liquid He stage. The signal utilized for imaging is the change of the sample voltage caused by the beam irradiation. A theoretical analysis of the heat balance equation indicates that the voltage signal reaches a maximum at the hotspot boundaries where the temperature profile passes through the critical temperature value of the superconductor. The predictions of our theoretical model agree well with our experiments performed using films of pure Sn, O2-doped Sn, and O2-doped Al. The width of the signal peaks marking the hotspot boundaries is twice the thermal healing length of the film/substrate configuration.

Advances in γ-γ-coincidence scintigraphy with the scintillation camera

A scintigraphic system consisting of an Anger camera and additional detectors is presented which allows imaging of an object by measuring gamma - gamma -coincidences. The additional detectors are in opposite arrangement, each with a focusing slit collimator viewing a plane parallel to the camera head. Imaging of hot spots and cold nodes in extended objects in this way will result in considerable contrast enhancement, which is shown by phantom studies. The sensitivity of the system will be significantly increased by using pinhole collimators.

ACCURACY OF CONTRAST ENHANCED COMPUTERIZED TRANSMISSION TOMOGRAPHY (CT) FOR SIZING ACUTE MYOCARDIAL INFARCTIONS

The purpose of this study was to assess the accuracy of CT for sizing acute myocardial infarctions (AMIs) under ideal (ex vivo) conditions; determine this in relation to the time between contrast medium (CM) administration and imaging; and compare accuracy of sizing by CT with scintigraphy using perfusion and hot spot imaging agents. AMIs were produced in 14 anesthetized mongrel dogs by ligation of a large obtuse marginal branch of the circumflex coronary artery. Forty eight hours after AMI the animals were sacrificed and the ex situ hearts were immediately scanned. Tc-99m pyrophosphate (PYP) and Thallium-201 (T1) were injected IV at 45 and 12 mins. presacrifice, respectively. Six dogs had CM injected at 10 mins. pre-sacrifice (infarct enhancement phase) and six dogs had CM injected at 1 min. prior to sacrifice (perfusion phase). CT was performed using an EMI 1005 scanner with 8 mm slice thickness. Following CT, the hearts were sectioned from apex to base and stained with nitroblue tetrazolium (NBT), followed by morphometric determination of infarct volume (true volume). Scintiphotos of the slices were obtained immediately for the PYP, and after a 24 hr. delay for the T1. The infarcted area of each slice was digitized and infarct volume was calculated by computer for all four modalities. Correlation between true volume and CT volume during the contrast enhancement phase was high (r = .97). Perfusion phase CT volume significantly underestimated infarct size and had only fair correlation with true volume (r = .67). T1 underestimated infarct size (r = .87) while PYP considerably overestimated infarct size and had a poor correlation with true volume (r = .55). We conclude that CT has the potential for accurate sizing of AMIs when performed during the enhancement phase while CT during perfusion phase and T1 scans underestimate and PYP markedly overestimates infarct size.

Radiopharmaceuticals in cardiovascular nuclear medicine

A plethora of radiochemicals and radiopharmaceuticals have been evaluated over the last two decades for assessing cardiac function and myocardial tissue viability and integrity. These have achieved varying degrees of success in clinical trials. With many of these agents, the radiation doses are extremely high and clearance characteristics are not suitable for prompt diagnostic utility. During the last few years, successful development of three agents: 99mTc-red blood cells, particularly by in vivo labeling technique for cardiac function dynamics; 99mTc-stannous pyrophosphate for hot spot imaging of myocardial infarcts; and 201Tl for myocardial perfusion and ischemia has given the noninvasive nuclear medicine procedures a most sought after status in the workup of cardiac patients. The availability of metabolic substrates labeled with ultra shortlived positron emitters in conjunction with sophisticated imaging devices has added yet another potential new dimension to the diagnostic capability for quantitating myocardial metabolic integrity, though this procedure is limited to a few centers with cyclotron facilities. The goal for labeling specific myocardial localizing agents with 99mTc or other intermediate half-lived radionuclides remains still elusive, though interesting leads are being pursued at present.