Electron-beam CT

A new method using ultrarapid computed tomography (spiral CT, ultrafast CT, electron-beam CT) minimizes artifact owing to motion of the heart during contraction and relaxation and provides a semiquan-titative assessment of calcium content in coronary arteries. Calcium scores greater than 150 provide a sensitivity of 74% and specificity of 89%, and this method may be cost-effective compared with ETT. 

Becker CR, Knez A, Jakobs TF et al (1999) Detection and quantification of coronary artery calcification with electron-beam and conventional CT. Eur Radiol 9 620-624 Callister TQ, Cooil B, Raya SP, Lippolis NJ, Russo DJ, Raggi P (1998) Coronary artery disease improved reproducibility of calcium scoring with an electron-beam CT volumetric method. Radiology 208 807-814 Fleischmann D, Hallett RL, Rubin GD (2006) CT angiography of peripheral arterial disease. J Vase Interv Radiol 17 3-26... 

Achenbach S, Moshage W, Ropers D, Bachmann K (1998) Curved multiplanar reconstructions for the evaluation of contrast enhanced electron beam CT the coronary arteries. Am J Roentgenol 170 895-899... 

EBCT electron beam CT MRDCT multi-row detector computed tomography... 

Achenbach S, Ropers D, Holle J et al. (2000) In-plane coronary arterial motion velocity measurement with electron-beam CT. Radiology 216 457 463... 

Electron-beam CT (EBCT) enabled exact localization of coronary stents and indirect evaluation of stent patency by cine loop evaluation and time-attenuation curve analysis (Mohlenkamp et al. 1999 Pump et al. 1998, 2000 ScHMERMUND et al. 1998). However, EBCT has been replaced by MDCT at most sites, mainly because of limitations in spatial resolution. 

Pugliese F, Weustink AC, Van Mieghem C et al. (2007) Dualsource coronary computed tomography angiography for detecting in-stent restenosis. Heart doi 10.1136/hrt.2007 Pump H, Moehlenkamp S, Sehnert C etal. (1998) Electron-beam CT in the noninvasive assessment of coronary stent patency. Acad Radiol 5 858 862... 

Knollmann FD, Kapell S, Lehmkuhl H, Schulz B, Bottcher H, Hetzer R, Felix R (2004) Dynamic high-resolution electron-beam CT scanning for the diagnosis of bronchiolitis obliterans syndrome after lung transplantation. Chest 126 447-456... 

Similar studies in a mass spectrometer, by using the electron beam to provide an initial distribution of excited ions, have bcHui interpreted semicpiantitatively in terms of the RRK model (D. P. Stevenson, private communication). However, the data are much less precise, and the assumptions needed to use them are open to considerable question. A similar theory has been used with some success to account for the mass spectral patterns of hydrocarbons, H. M. Rosenstock ct al., Proc. NaVl Acad. Sci. U.S.t 38, 667 (1962). 

Guerci AD, Spadaro LA et al. (1998) Comparison of electron beam computed tomography scanning and conventional risk factor assessment for the prediction of angiographic coronary artery disease. J Am Coll Cardiol 32 673-679 Haberl R, Becker A et al. (2001) Correlation of coronary calcification and angiographically docmnented stenoses in patients with suspected coronary artery disease results of 1,764 patients. J Am Coll Cardiol 37 451-457 Hacker M, Jakobs T et al. (2005) Comparison of spiral multidetector CT angiography and myocardial perfusion imaging in the noninvasive detection of functionally relevant coronary artery lesions first clinical experiences. J Nucl Med 46 1294-1300... 

Hacker M, Jakobs T et al. (2007) Sixty-four slice spiral CT angiography does not predict the functional relevance of coronary artery stenoses in patients with stable angina. Eur J Nucl Med Mol Imaging 34 4-10 He ZX, Hedrick TD et al. (2000) Severity of coronary artery calcification by electron beam computed tomography predicts silent myocardial ischemia. Circulation 101 244-251 Hoffmann MH, Shi H et al. (2005) Noninvasive coronary angiography with multislice computed tomography. JAMA 293 2471-2478... 

Fig. 5.6 Series of four subsequent STEM micrographs of 0.03 e/nm Pt s The images are recorded with an electron beam of 300kV two cluster pairs that coalescence as a result of the high beam intensity are marked with circles. ai = 0s,bt = 82s,ct = 138s,dt = 219s...

Therefore it is reasonable to prepare already the data acquisition for a three dimensional evaluation in cone-beam-technique by means of two-dimensional detectors. The system is already prepared to integrate a second detector- system for this purpose. An array of up to four flat panel detectors is foreseen. The detector- elements are based on amorphous silicon. Because of the high photon energy and the high dose rates special attention was necessary to protect the read-out electronics. Details of the detector arrangement and the software for reconstruction, visualisation and comparison between the CT results and CAD data are part of a separate paper during this conference [2]. 

The overall approach relies on the determination of accurate rate constants for the reaction of the chiral C-0 carbon. The rate equation is dn/dl = -ufn, where the reaction cross section is ct (cm2). Straightforward integration yields n(Q/n(0) = e n - where c = Jf(t)dt is the photon exposure. Note that in general the photon flux fit) varies with time so the integral must be used. However, the APS operates in top-up mode where the beam current of the stored electrons is kept nearly constant by injection every few minutes. Thus/(f) = constant = / and the resulting equation is n(Qln( 0) = where/is the flux density and f is the time. The time... 

Before discussing possible mechanisms that could explain these results, it is worthwhile comparing the time constants to results from previous electron-induced surface chemical reactions. The extracted time constant, t, equals 1/ct/, where/is the X-ray flux density and % is the photolysis cross section. Using approximate values of the beam area (3 x 10 4 cm2) and X-ray flux (3.5 x 10n ph/s), yields a flux density of 1.7 x 1015 ph/s cm2 and a a of 6 x 10-19 cm2. Our results show that it is the secondary electrons that are inducing the chemical changes. Therefore, it is more applicable to use the secondary electron flux to compute the cross section. An upper bound to this is given by the TEY flux density. This is determined from the measured sample current of 3.8 nA or 2.4 x 1010 e/s, which results in a cross section of 9 x 10 18 cm2 (9 Mb) This value compares fairly well with reported dissociative electron impact cross sections for CO production from condensed films of acetone (9.6 Mb) [124] or methanol (4.2 Mb) [125] via a DEA mechanism. In the present case a DEA mechanism, in which a temporary negative ion state is formed,... 

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