MRI of Integrins
Integrins, such as av03 are over-expressed in activated neovascular endothelial cells, which are believed to play an integral role in tumor growth and the initiation and development of atherosclerosis. Wickline, Lanza and co-workers have developed perfluoro-nanoparticles that can carry as many as 90,000 paramagnetic Gd chelates per particle and which can be targeted against various biomarkers by attaching appropriate ligands. In a recent study, they directed such nanoparticles to the...
Quantification Of Myocardial Blood Flow And Metabolism In Rodents
Once the technical aspects for quantifying blood and myocardial activity have been optimized it is then possible to apply well validated kinetic models to measure biologically relevant parameters such as MBF and myocardial metabolism. Discussed below are two such examples. MBF Alterations in MBF are central to normal cardiac performance and play key role in a variety of cardiac disorders such as myocardial ischemia, left ventricular hypertrophy and heart failure. Using well-validated...
T1 Measurements
Measurements of the T1 relaxation time are usually performed with inversion recovery sequences. By changing the inversion delay TI between the non-selective inversion prepulse and data acquisition, signal from tissue A T1 T1A will be nulled if the inversion delay TI fulfills the condition TI T1A x ln 2. Most T1 measurements approaches are based on the Look and Locker sequence, which acquires multiple images 6-11 along the T1 relaxation curve after an initial inversion prepulse 10 . Several new...
Thrombus
Thrombus-targeted microbubbles have been developed to improve the diagnostic accuracy of ultrasound for detecting vascular or intracardiac thrombi. One strategy for has been to target microbubbles to the platelet glycoprotein Ilb IIIa receptor that is expressed at a very high density on the surface of platelets upon Figure 8 Molecular imaging of ischemia and growth factor-mediated angiogenesis with targeted microbubbles. Top Signal enhancement in ischemic hindlimb skeletal muscle in rats...
Clinical Studies
Histopathologic validation of qualitative and quantitative image criteria ex vivo provided a foundation for interpreting data obtained from living human patients. Between January 2000 and September 2003, a total of 83 patients undergoing routine percutaneous transluminal coronary intervention PTCI were enrolled in a study at the Massachusetts General Hospital Boston, Massachusetts, U.S.A. to investigate the feasibility of intracoronary OCT. Imaging was performed in culprit lesions and remote...
MRI OF ATHEROSCLEROSIS MultiContrast MRI of Atherosclerosis
Multi-contrast MRI entails delineating different components of atherosclerotic lesions by generating T1-weighted, T2-weighted and proton-density weighted images of plaque 18,37,38 . This has largely become possible because of faster imaging methods, the ability to perform high-resolution scans and better detection coils RF coils . The multi-contrast MRI approach involves characterization of plaque based upon signal intensities as well as morphologic appearance of various plaque components on...
References Gka
1. Clardy J. Borrowing to make ends meet. Proc Natl Acad Sci U S A 1999 96 5 1826-1827. 2. Lucretius. On the Nature of the Universe. Translated by Latham RE. London Penguin Books, 1951 149-152. 3. Ehrlich P. In Himmelweit F, Marquardt M, Dale H, eds. Ehrlich P. The assay of the activity of diptheria-curative serum and its theoretical basis. Volume II-IV. London Pergamon Press, 1957. 4. Langley JM. On nerve endings and special excitable submstances in cells. Proc R Soc B 1906 8 170. 5. Kenakin...
T2 Maps
T2 maps are acquired by sampling the signal along the free induction decay FID curve using multiple TE at a constant TR. The most common approaches are based on gradient echo sequences with signal sampling along Cartesian trajectories 13,14 . The drawback is the relatively long scanning time with this approach. In a recent study, Schaeffter and coworkers proposed a faster approach by taking advantage of the undersampling properties of radial imaging 15 . Undersampled radial sub-images with...
References Abd
1. Lindner JR, Song J, Jayaweera AR, Sklenar J, Kaul S. Microvascular rheology of definity microbubbles following intra-arterial and intravenous administration. J Am Soc Echocardiogr 2002 15 396-403. 2. Skyba DM, Camarano G, Goodman NC, Price RJ, Skalak TC, Kaul S. Hemodynamic characteristics, myocardial kinetics and microvascular rheology of FS-069, a second generation echocardiographic contrast agent capable of producing myocardial opacification from a venous injection. J Am Coll Cardiol 1996...
Mapping Of The Conduction System Of The Heart
Optical mapping has made a significant contribution to functional studies of impulse propagation in the conduction system of the heart. The structural complexity of the right atrial preparation, especially in the nodal areas, makes it difficult to apply conventional electrode mapping techniques. While in unipolar elec-trograms, the distinction between local and distant events is often impossible, bipolar electrograms represent complex spatial derivatives of the underlying spatio-temporal...
Targeted Microbubble Design And Detection
Acosutically active agents for molecular imaging have been developed using two different targeting strategies Fig. 3 . The first and more simple strategy involves the manipulation of the chemical or charge properties of the microbubble or microparticle shell. The shells of microbubbles, nanoparticles, or liposomes may also be modified by the surface conjugation of ligand molecules, such as monoclonal antibodies, peptides, glycoproteins, etc. Most formulations involve surface conjugation of...
microPET Technology
The prototype microPET scanner was developed by Cherry et al. 42 at UCLA in 1996. Its technology was made commercially available by Concorde Microsystems Inc., Knoxville, Tennessee, U.S.A. now part of Siemens Molecular Imaging in 2000. The second prototype system, microPET II, was completed in 2002 at UC Davis by the same group 49 , and the third generation microPET developed at Concorde was revealed in 2003 Focus 220 51 and 2004 Focus 120 52 . Figure 10 shows photographs of the micro PET...
Intravascular Ultrasound Imaging
To help diagnose and treat cardiovascular disease, intravascular ultrasound imaging was developed to visualize arterial pathologies from the vessel lumen. IVUS Image of Diseased Coronary Artery with Intimai Flap IVUS Image of Diseased Coronary Artery with Intimai Flap IVUS Image of Dissection post Balloon Angioplasty Figure 1 Two typical B-Mode clinical images obtained with a 3.5F imaging catheter. Left A diseased artery with an intimal flap. Right Arterial dissection post angioplasty on the...
Attenuation Correction
When either or both annihilation photons are absorbed by the object or scattered out of the FOV, the original decay event is undetectable. The probability that a photon survives is not attenuated as it travels through matter is inversely proportional to the exponential of the line integral of the attenuation coefficient along its path. Therefore, the attenuation correction for detecting a single photon depends on the depth of the source. However, with coincidence detection in PET, the...
Development In Animal Handling Techniques
The first hurdle in obtaining quantitative data, in particular in mice, is the development of animal handling methods that result in minimal trauma to the animals. Furthermore, in PET studies of the heart, multiple tracer administrations to a single animal are frequently necessary to perform measurements of both myocar-dial perfusion and the metabolism of various substrates such as oxygen, glucose, and fatty acids. Due to the inherent rapid kinetics of flow and metabolic PET...
Passive Targeting
Examples of passive targeting agents are iron oxide particles that may be used to label components of the reticuloendothelial system RES . SPIO nanoparticles diameter 200 nm are recognized by the RES and are rapidly removed from the blood stream 36 . SPIO uptake detectable by MRI and histology has been found in atherosclerotic plaques of hyperlipidemic rabbits in regions of high macrophage content 37 . USPIOs diameter 20 nm are not immediately scava-gened by the hepatic and splenic RES, so they...
Cardiac Reporter Gene Imaging Studies
While most molecular imaging studies have focused on cancer biology 33,34 , only recently has reporter gene imaging of cardiac transgene expression been investigated. In the following section, a summary of some of the most relevant studies published over the past years will be discussed. In the first proof-of-principle study involving cardiac optical bioluminescence imaging, adenovirus with a constitutive cytomegalovirus CMV promoter driving firefly luciferase reporter gene Ad-CMV-Fluc 1x109...
Radiopague Indicators Of Physiological Spaces And Processes
Essentially all current X-ray micro-CT scanners, like clinical CT scanners, use the attenuation of the X-ray by tissues as the signal for generating the X-ray images. In micro-CT scanners, this means that for a given X-ray photon energy the contrast signal is most closely related to the atomic number Z and the concentration of that element 45 . At the X-ray exposures tolerated by living tissues, this means that the signal-to-noise in the CT image is adequate primarily for differentiating air,...
Imaging Capability of microPET
High-resolution imaging capability of microPET is demonstrated in Figure 13. A micro-Derenzo phantom with hot rods of different sizes was imaged by P4, Focus 220 and microPET II. The diameter of rods is 0.8, 1.0, 1.25, 1.5, 2.0, and 2.5 mm respectively. The center-to-center distance between adjacent rods is 2 times the rod diameter. It is evident that Focus 220 has a higher resolution than P4, while the microPET II has the highest resolution. With the maximum a posteriori MAP 65,66...
References Cwq
1. Wernick MN, Aarsvold JN, eds. Emission Tomography The Fundamentals of PET and SPECT. Philadelphia Elsevier Mosby, 2004. 2. Barrett HH, Myers KJ. Foundations of Image Science. Hoboken John Wiley and Sons, 2004. 3. Beekman FJ, Vastenhouw J. Design and simulation of a high-resolution stationary SPECT system for small animals. Phys Med Bio 2004 49 4579-4592. 4. Germano G, Berman S. Regional and global ventricular function and volumes from single-photon emission computed tomography perfusion...
Random and Scatter Corrections
The coincidence events detected by a PET scanner can be divided into three categories Fig. 7 . If the annihilation photons escape the object without any interaction and subsequently become detected by the scanner, this is defined as a true coincidence, illustrated as event A. If at least one of the two 511 keV photons is scattered by the object, such as event B in Figure 7, this is a scattered coincidence. If two uncorrelated 511 keV photons are detected within the predefined timing window,...
Implementation of Correction Techniques in microPET
Random coincidences were initially measured by all microPET systems using the delay-window technique. Figure 11 Photographs of various microPET detectors. A Detectors of the prototype microPET top and microPET II bottom . The MC-PMT in the prototype detector was much larger and required long optical fibers. microPET II detector uses fused optical fiber bundle, compact MC-PMT and 14 x 14 elements LSO array with sub-millimeter crystal width as shown in C next to a penny . B Detector in the first...
Dead Time Correction
A photon counting system takes a certain amount of time to process an event. The period of time that a system can not accept an additional event is called dead time. For simple systems, the system dead time may be characterized as paralyzable or non-paralyzable 27 . A paralyzable system takes time to recover after the latest event, even if that event is not detected. For example, if a second event occurs before the system finishes processing the first event, the system will be dead for an...