Reconstruction Algorithms based on Feldkamp’s Methods
Introduction
Image reconstruction from projection data has been the subject of many studies. It is an attractive field generally in digital image processing techniques, especially in biomedical imaging. It has been strongly developed and practically implemented in almost every modern tomographical modalities. Image diagnostic equipments such as CT scanners, MRI, 3D-4D ultrasound etc. have been used widely in developed countries.
All recent medical 3D image reconstruction techniques create 3D images from sets of 2D slices, which can be recorded by various equipments such as CT, MRI, ultrasound etc. Each type of scanner has his own characteristics due to physical principles of image recording, e.g. images of CT scanner are often parallel slices with high contrast, images of ultrasound scanner are either parallel or divergent slices with low contrast etc.
The word tomography itself is composed of the two Greek words tomos (slice) and graphein (draw). Computerized Tomography (CT) is a technique for imaging the cross sections of an object using a series of x-ray measurements taken from different angles around the object.
Computed tomography (CT) has evolved into an indispensable imaging method in clinical routine. It was the first method to non-invasively acquire images of the inside of the human body that were not biased by superposition of distinct anatomical structures. This is due to the projection of all the information into a two dimensional imaging plane, due to which, CT yields images of much higher contrast compared with conventional radiography.
Recently, interesting technical, anthropomorphic, forensic, and archaeological (Thomsen et al. 2003) as well as paleontologi...
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...ass filter is required to backproject the projection data which can be given by the formula:
Where cos(β) is the weight & g(a) represent the filter kernel.
3. The filtered backprojection is then given by :
Many modifications of the FDK algorithm have been developed over the years to get even better results.
The term “computed tomography” is historically connected to the development of computers, which have been successfully applied in the field of image reconstruction since the 1960s.
A projection represents an averaging. It would be difficult for to interpret the results, as averaging comes along with a considerable reduction in contrast, compared with the contrast present in one slice.
Conventional CT produces two-dimensional slices. However, CT becomes a three dimensional imaging modality if consecutive slices are arranged as axial stacks.
A study performed by Martin Hausler and Peter Schmid of the University of Zurich, Switzerland, appeared in the October 1995 issue of Journal of Human Evolution, igniting controversy over the 1974 Australopithecus discoveries in Hadar, Ethiopia. The most famous of the Hadar specimens is the 3-million-year-old skeleton, “Lucy,” who was recovered by paleoanthropologist, Donald Johanson. In his article, Shreeve presents the methods and findings of Hausler and Schmid’s study as well as some counter arguments from other scientists in the field.
Feder and Park present a list of traits that are used by paleoanthropologists to distinguish the appearance of skeletal features and characterize these changes over time. Th...
Recently, new advances have been made in PET technology. A pair of American scientists working in Switzerland came up with a combination PET/CT scanner, which effectively pairs the two techniques. This new combination will be very useful in cancer diagnosis. With the PET/CT, both anatomical and functional imaging can be done and reproduced on the same image. This will be helpful in pinpointing the location of tumors, and also for the early identification of tumors too small to be of concern in CT scanning.
by the internal computers of the instrument, to create an image of internal body tissues. These images were then displayed on the screen for the user,
Shubin, N.H., & Marshall, C.R. 2000. Fossils, genes and the origin of novelty. Paleobiology, 26(4): 324-340.
...tance, which creates contrast, and having a Magnetic Resonance Imaging scan, Computed Tomography (CT) scan, or a fluoroscopic X-ray.
To begin with, how has technology changed the field of radiology? Since the discovery of X-radiation there has been a need and desire for studying the human body and the diseases without actually any intervention. Over the past fifty years there has been a revolution in the field of radiology affecting medicine profoundly. “The ability to produce computers powerful enough to reconstruct accurate body images, yet small enough to fit comfortably in the radiology department, has been the major key to this progress”(Gerson 66). The core of radiology’s vast development consists of four diagnostic techniques: computed tomography (CT), digital subtraction angiography (DSA), ultrasonography, and magnetic resonance imaging (MRI). These methods of diagnostic imaging provide accurate information that was not seen before. Amid this information advancement, radiologists have broadened their role of diagnostician. Gerson writes, “With the advent of computer-enhanced imagery and new interventional techniques, these physicians are able to take an active part in performing therapeutic procedures”(66). A radiology breakthrough in 1972 was computed tomography discovered by Godfrey Hounsfield and Allan Cormack. Unlike standard radiography, computed tomography would spin the X-ray tube 360 degrees and inversely another 360 degrees while the patient ta...
Bindon, Jim 2004 Fossil Hominids. ANT 270 Notes. http://www.as.ua.edu/ant/bindon/ant270/lectures/ hominids1.pdf Delson, Eric 1981
Getting an MRI is a non-invasive method used to look at images inside an object. MRI’s are mainly used to observe pathological or physiological developments of living tissues. The patient simply lies on his or her back and slides onto the bore- the tube running through the magnet. An MRI’s job is to find tissue and determine what it is, by using radio wave pulses of energy. The MRI creates 2-D or 3-D images of each point in the patient’s body. The MRI system can cause tissues in the body to take on different appearances, which is helpful to radiologists who read it. It can also show flowing blood to help show the arterial system.
Magnetic Resonance Imaging (MRI) is one of the medical imaging modality which provides excellent internal structures of the body using magnetic radiation (WHO, 2014). Better Health Channel (2011) suggested MRI is notably helpful visualizing contrasts of body organs and soft tissues, WHO pointed out MRI generates excellent images of the brain, spine, muscles, joints and other body structures. The images generated by the MRI machine is multiplanar, this means the image is obtained in multiple planes of the body without the patient changing its body position (WHO, 2014). MRI can also be viewed in 3D (Southern Radiology).
"Imaging and radiology." Magill's Medical Guide, 4th Rev. ed.. 2008. eLibrary. Web. 16 Dec. 2013.
According to Orth & Goske, 2009, the effective dose of a pediatric chest CT exam is 300 times that of a plain chest radiograph. The author poses the point that pediatric patients receive a higher dose than necessary if an adult technique is set; Children likely receive a higher dose from an adult technique due to the larger size setting (National Cancer Institute, n.d.). This was confirmed by a study that simulated the doses on phantom subjects. Due to the way CT delivers radiation in a rotating fashion, the dose at the center of a patient’s body is less than the dose received at the surface (Orth & Goske, 2009). This would mean the thicker a patient is, the more dose is absorbed before it reaches the midpoint or core of the body, effectively lowering a patient’s core dose. Pediatric patients are naturally smaller than their adult counter-parts, so they likely receive a higher core dose of radiation from each CT study. The specific pediatric organs susceptible to radiation are outlined well by the authors. The audience will find it easy to process information on radiation, because the authors compare it to everyday background
CTscans stands for “Computed Tomography”. It is a way of looking inside your body using a special camera. It is an advanced scanning x-ray and computer system that makes detailed pictures of horizontal cross-sections of the body, or the part of the body that is x-rayed. A CT scan is a diagnostic test that combines the use of x-ray with computer technology. A series of x-beams from many different angles are used to get these cross-sectional images of the patient’s body. In a computer, these pictures are assembled into a 3-dimentianal picture that can display organs, tissues, bones, and any such thing. It can even show ducts, blood vessels and tumors. One of the advantages of CT is that it clearly shows soft tissue structures (such as brain), as well as dense tissue structure (such as bone). The pictures of a Ctscanner are a lot more detailed than the pictures of a regular X-ray machine. It can make pictures of areas protected or surrounded by bones, which a regular X-ray machine can not. Because of this, a CT scanner is said to be 100 times as affective and clever as an ordinary X-ray, and can therefore diagnose some diseases a lot earlier and quicker. It is recent technology that has made it possible to accurately scan objects into a computer in three dimensions, even though the machines and ideas were developed in the 1970s. In the 70s doctors started to use this new type of machine that could give detailed pictures of organs that the older type of x-ray, machine could not give.
Images of human anatomy have been around for more than 500 years now. From the sketches created by Leonardo da Vinci, to the modern day Computed Tomography (CT) or Magnetic Resonance Imaging (MRI) scan, images have played a great role in medicine. Evolution in medical imaging brought together people from various disciplines such as Biology, Physics, Chemistry and Mathematics, a collaboration which has further contributed to healthcare as a whole. Modern day imaging improves medical workflows by facilitating a non-invasive insight into human body, accurate and timely diagnostics, and persistence of an analysis.
Medical tools in the modern day are almost all made with small, programmed computers inside. “Medical imaging is a vast field that deals with the techniques to create images of the human body. Many of the modern methods of scanning and imaging are largely based on computer technology” ("Importance of Computers in Medicine."). We have been able to apply many of the advanced medical imaging techniques, over the years, thanks to developments in computer science. Magnetic quality imaging uses computer software. To obtain high-resolution images, doctors ...