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The role of imaging is now becoming ever more important in patient management. With the now widespread use of different imaging techniques, it has become clear that there are several ways of investigating the same condition through diagnostic imaging. Diagnostic imaging is a term used to refer to those technologies used by doctors in examining the body to establish any medical condition (Armstrong, Wastie & Rockall, 2004). There are various machines and techniques that can create pictures of the human body. Doctors use various technologies in examining the body for clues about a medical condition. Many diagnostic imaging tests are painless and easy. Nevertheless, they may require one to stay for a long time in the machine.

The science of radiology has its beginning towards the end of the 19th century when a Dutch physicist, Wilhelm Conrad Roentgen, discovered a form of radiation that he named x-ray since he could not understand its nature (Armstrong, Wastie & Rockall, 2004). In the first decade of the discovery of x-ray, the physical effects of x-rays on patients were also observed. It was not long before a new medical specialty known as radiology was born. Traditionally, radiology was divided into diagnostic and therapeutic. The only common area between these disciplines was the use of ionizing radiation. The last quarter of the twentieth century was marked by changes in diagnostic radiology that superseded those made in the first three quarters of the century (Daffner, 2007).

 Developments in recent decades have revolutionized medical diagnosis, making areas of the body previously inaccessible to surgical examination clearly visible. The realm of diagnostic radiology encompasses various modalities of imaging that may be used individually or, more commonly, in combination to provide the clinician with enough information to aid in making  diagnosis. Diagnostic imaging includes radiography with and without contrast enhancement, computed tomography, magnetic resonance imaging, diagnostic ultrasound, and nuclear imaging (Armstrong, Wastie & Rockall, 2004). The first three of these imaging forms use X-rays.

The first diagnostic imaging modality to be examined in this paper is the computed tomography. Under ordinary circumstances, the fleshy organs of the body such as the heart and kidneys are considered uniform in radiographic density if examined using conventional radiographs (Brant & Helms, 2009). However, these tissues vary somehow in their chemical properties, and it is possible, using computer-enhanced techniques, to measure those differences, magnify them, and display them in varying shades of gray or in color. This is the basis for computed tomography. The first CT machine was developed by Godfrey Hounsfield in England, and for these efforts, he was awarded the Nobel Prize in medicine in 1979 (Brant & Helms, 2009).

In CT, the subject is irradiated using an x-ray beam, as well as a detector system that moves all around the body of the patient. This allows the system detector to measure the intensity of radiation passing through the subject (Erkonen & Smith, 2009). The data obtained from the measurements are fed to a computer system for analysis. The computer system then assigns different shades of gray to different structures based on their absorption or attenuation coefficients. A picture is reconstructed by the computer which is based on geometric plots of where the measurements were derived from. Despite the CT having being discovered in the early 1970s, the system uses a mathematical formula that had been developed by Johann Radon earlier in 1917 (Armstrong, Wastie & Rockall, 2004).

One of the modern versions of CT technology is known as helical or spiral CT. In helical CT, the patient table is moved at a steady pace through the CT gantry as the scanning process continues while an x-ray tube rotates about the patients body. A constant volume of data is obtained during a single breath-hold. This technique has dramatically improved the speed of acquiring image. It also makes scanning possible especially during finest contrast opacification. It also eliminates artifacts that are occasioned by mis-registration and differences in patients breathing (Brant & Helms, 2009).

The information obtained using CT systems is displayed on a television CRT monitor and recorded on CD or DVD. Once the information has been recorded, it is possible to alter the windows of the various densities to optimally demonstrate the various subject organs on the reading console. The data from the CT is linked to a digital display such as PACs or teleradiology (Daffner, 2007). It may also be transferred to x-ray film using a device known as a multi format camera. The appearance of certain viscera or vascular neoplasms is enhanced by injecting contrast material intravenously. The latest technical advance in CT imaging is known as multi-detector helical CT (MDCT). It uses the helical priciples; scanner, however,  includes numerous rows of detector rings (Herring, 2007). This enables the attainment of many slices in every tube rotation; hence augmenting the patient’s area that can be enclosed by a single x-ray beam.

The key benefit of MDCT is its pace.  Compared to helical CT, this version is five to eight times. For body scanning, one millimeter slices can be obtained creating cubic isotropic voxels, which allows image reconstruction in any anatomic plane without losing resolution (Daffner, 2007). A disadvantage of MDCT is radiation dose, which can be three to five times higher than with single-slice CT. During a CT imaging test, the patient lies on table attached to the CT scanner. The machine then sends x-ray through the body part under study. Every rotation of the CT scanner takes slightly under one second and offers a picture of a thin slice of the body part under examination. The pictures are then saved in a computer, and can also be printed. A CT imaging test can be used to study almost all parts of the body like the lung, liver, heart, thyroid and even bones (Erkonen & Smith, 2009).

The second diagnostic imaging modality to be examined in this paper is magnetic resonance imaging (MRI). This is a technique that produces tomographic images by means of radio waves and magnetic fields. As examined earlier, CT evaluates only a single tissue parameter through x-ray attenuation. However, MRI analyzes multiple tissue characteristics including proton density, T1 and T2 relaxation times of tissues, and blood flow inside the tissue. The soft tissue gap provided by MRI is considerably better compared to what can be obtained using any other imaging modality (Armstrong, Wastie & Rockall, 2004). T1 is a measurement used to determine how fast a tissue can be come magnetized (Brant & Helms, 2009). On the other hand, T2 coveys how quickly a given tissue loses its magnetization.

MRI is grounded on the premise that a small number of protons can absorb and release radio wave energy if the body is subjected to a strong magnetic field. Dissimilar tissues absorb and emit radio wave energy at different, detectable, and characteristic rate. MRI scans are gotten when the patient is placed in a static magnetic field of 0.02 to 4 teslas in strength, depending on the particular MRI unit used. The choice of unit for imaging is based on preference and local availability (Daffner, 2007). A small number of tissue protons in the patient align with the main magnetic field and are subsequently displaced from their alignment by application of radio frequency gradients. When the RF gradient is terminated, the protons that have been terminated align again with main magnetic field, releasing a small pulse of energy that is detected, localized, and then processed by a computer algorithm similar to that used in CT to produce a cross-sectional tomogrophic anatomic image. MRI can be used to image different  body parts such as the, bones, spine, joints, pelvic organs, urinary tract, and heart. It is a useful procedure for diagnosing skeletal diseases and cancer (Erkonen & Smith, 2009).

The last diagnostic imaging modality is ultrasound. This modality uses very high frequency sound that is directed into the body of a patient. The transducer that produces the sound is positioned in contact with the skin. A good acoustic contact is obtained by smearing the body of the patient with jelly-like substance. As the sound moves through the body, the tissue interfaces reflect it, hence producing echoes which are picked by the same transducer and afterwards is translated into an electrical signal. Ultrasound is generated by making a special crystal oscillate at a frequency  that is predetermined. The crystal not to transmits the pulses of sound and ‘listens’ to the bouncing echoes. The echoes are amplified by electronic means and recorded on a television monitor in the form of signals (Herring, 2007).

During the scan, the ultrasound beam is electronically passed through the patient’s body and body part is showed instantly. The obtained image appears like a slice, and for one to get a three-dimensional assessment; a number of slices must be created by angling or moving the transducer (Brant & Helms, 2009). An ultrasound scan can be used for various uses. It can be used to keep a watch on the progress of a child that is yet to be born. Ultrasound can also be used to identify problems of different body parts such as the liver, pancreas, ovaries, kidneys, and breast. In essence, the different diagnostic imaging modalities have been a milestone in the medical history as they have helped doctors in examining various body parts that could not have been examined were it not for the developments. 

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