Definition
Emission Computed Tomography is a technique where by multi cross sectional images of tissue function can be produced , thus removing the effect of overlying and underlying activity. The technique of ECT is generally considered as two separate modalities. SINGLE PHOTON Emission Computed Tomography involves the use single gamma ray emitted per nuclear disintegration. Positron Emission Tomography makes use of radio isotopes such as gallium-68, when two gamma rays each of 511KeV, are emitted simultaneously where a positron from a nuclear disintegration annihilates in tissue.
SPECT, the acronym of Single Photon Emission Computed Tomography is a nuclear medicine technique that uses radiopharmaceuticals, a rotating camera and a computer to produce images which allow us to visualize functional information about a patient's specific organ or body system. SPECT images are functional in nature rather than being purely anatomical such as ultrasound, CT and MRI. SPECT, like PET acquires information on the concentration of radio nuclides to the patient's body.
SPECT dates from the early 1960 are when the idea of emission traverse section tomography was introduced by D.E.Kuhl and R.Q.Edwards prior to PET, X-ray, CT or MRI. THE first commercial Single Photon- ECT or SPECT imaging device was developed by Edward and Kuhl and they produce tomographic images from emission data in 1963. Many research systems which became clinical standards were also developed in 1980's.
SPECT is short for single photon emission computed tomography. As its name suggests (single photon emission) gamma rays are the sources of the information rather than X-ray emission in the conventional CT scan.
Similar to X-ray, CT, MRI, etc SPECT allows us to visualize functional information about patient's specific organ or body system.
Internal radiation is administrated by means of a pharmaceutical which is labeled with a radioactive isotope. This pharmaceutical isotope decays, resulting in the emission of gamma rays. These gamma rays give us a picture of what's happening inside the patient's body.
By using the most essential tool in Nuclear Medicine-the Gamma Camera. The Gamma Camera can be used in planner imaging to acquire a 2-D image or in SPECT imaging to acquire a 3-D imag
Definition
With the proliferation of portable electronic devices, power efficient data transmission has become increasingly important. For serial data transfer, universal asynchronous receiver / transmitter (UART) circuits are often implemented because of their inherent design simplicity and application specific versatility. Components such as laptop keyboards, palm pilot organizers and modems are few examples of devices that employ UART circuits. In this work, design and analysis of a robust UART architecture has been carried out to minimize power consumption during both idle and continuous modes of operation.
UART
An UART (universal asynchronous receiver / transmitter) is responsible for performing the main task in serial communications with computers. The device changes incoming parallel information to serial data which can be sent on a communication line. A second UART can be used to receive the information. The UART performs all the tasks, timing, parity checking, etc. needed for the communication. The only extra devices attached are line driver chips capable of transforming the TTL level signals to line voltages and vice versa.
To use the device in different environments, registers are accessible to set or review the communication parameters. Setable parameters are for example the communication speed, the type of parity check, and the way incoming information is signaled to the running software.
UART types
Serial communication on PC compatibles started with the 8250 UART in the XT. In the years after, new family members were introduced like the 8250A and 8250B revisions and the 16450. The last one was first implemented in the AT. The higher bus speed in this computer could not be reached by the 8250 series. The differences between these first UART series were rather minor. The most important property changed with each new release was the maximum allowed speed at the processor bus side.
The 16450 was capable of handling a communication speed of 38.4 kbs without problems. The demand for higher speeds led to the development of newer series which would be able to release the main processor from some of its tasks. The main problem with the original series was the need to perform a software action for each single byte to transmit or receive. To overcome this problem, the 16550 was released which contained two on-board FIFO buffers, each capable of storing 16 bytes. One buffer for incoming, and one buffer for outgoing bytes.
Definition
Computer chips of today are synchronous. They contain a main clock, which controls the timing of the entire chips. There are problems, however, involved with these clocked designs that are common today.One problem is speed. A chip can only work as fast as its slowest component. Therefore, if one part of the chip is especially slow, the other parts of the chip are forced to sit idle. This wasted computed time is obviously detrimental to the speed of the chip.
New problems with speeding up a clocked chip are just around the corner. Clock frequencies are getting so fast that signals can barely cross the chip in one clock cycle. When we get to the point where the clock cannot drive the entire chip, we'll be forced to come up with a solution. One possible solution is a second clock, but this will incur overhead and power consumption, so this is a poor solution. It is also important to note that doubling the frequency of the clock does not double the chip speed, therefore blindly trying to increase chip speed by increasing frequency without considering other options is foolish.
The other major problem with c clocked design is power consumption. The clock consumes more power that any other component of the chip. The most disturbing thing about this is that the clock serves no direct computational use. A clock does not perform operations on information; it simply orchestrates the computational parts of the computer.
New problems with power consumption are arising. As the number of transistors on a chi increases, so does the power used by the clock. Therefore, as we design more complicated chips, power consumption becomes an even more crucial topic. Mobile electronics are the target for many chips.
These chips need to be even more conservative with power consumption in order to have a reasonable battery lifetime.The natural solution to the above problems, as you may have guessed, is to eliminate the source of these headaches: the clock.
