Factors to Consider When Buying a CT Scanner

Technical specifications of available CT scanners are often quite extensive. Although it is helpful to review these for each CT scanner component, this may not reflect the relative clinical performance of the systems. It is also important to recognize that the performance in practice depends on the trade-off between image quality and radiation dose.

The time taken to complete a scan is a key factor in scanner performance and may limit the type of procedure that can be performed. In most cases, the limitation is set by the need to control artifacts due to involuntary patient motion, such as restlessness, or breathing and peristalsis.

CT Scanner design factors which affect the total scan time are the gantry rotation time and detector array design along the z-axis (scan axis).
The maximum scan length is governed by the z-axis detector array design, and the X-ray tube heat characteristics. With the large volumes of data generated with a 64 slice scanner, for example, the total scan length may also be limited by computer memory capacity.

The rotation time of the tube and the detectors around the patient has a direct effect on total scan time. Image quality will improve with faster rotation time, as there will be reduced misregistration of data arising from patient movement. This misregistration of data introduces artifacts into the image.

The length of the detector array determines the number of rotations needed to cover the total scan length, and thus the overall scan time. Multislice (MSCT) scanners cover a patient volume between 20 and 40 mm in length per rotation, and the latest diagnostic MSCT scanners can image patient volumes of up to 160 mm per rotation.

Complete coverage of an organ, such as the heart or the brain, offers advantages for both dynamic perfusion and cardiac studies. The z-axis detector array lengths of up to 80 mm on current scanners are adequate to cover these organs in only a few rotations. A coverage length of 160 mm usually allows complete organ coverage in a single rotation, so the function of the whole organ can be monitored over time.

Modern CT scanning techniques place a high heat load on the X-ray tube due to the need for high tube current values, in order to give enough photons in the image when scanning with fast rotations and fine slices. To scan a sufficiently long length, while avoiding overheating, X-ray tubes have generally been developed to have high anode heat capacities and high cooling rates. Some designs have low anode heat capacities, but very high cooling rates to compensate.

The principal parameters that describe image quality are: spatial resolution, contrast resolution, temporal resolution, and the prevalence of artifacts. The image quality actually achieved on any scanner depends not only on scanner design features, but also on scan parameters selected and patient-related factors, and will always be a compromise between image quality and radiation dose.

Modern MSCT scanners should be capable of achieving isotropic resolution: a z-axis resolution equal to, or approaching, the scan plane resolution, as this is essential for good quality multiplanar and 3D reconstructions.

Contrast resolution is the ability to resolve an object from its surroundings. The ability to detect an object will depend on its contrast, the image noise and the size.

Dose efficiency of the scanner is a significant factor in the examinations, as it will determine the dose required for a given level of contrast resolution.

In CT, temporal resolution is usually considered in the context of cardiac scanning. The aim is to minimize image artifacts due to the motion of the heart.

Generator power is an important factor in low-contrast examinations. Low noise images require high tube current values, particularly when coupled with fast rotation speeds and narrow slice acquisitions. Fast rotation speeds improve the temporal resolution and reduce movement artifacts.

Artifacts are defined as structures in the image that are not present in the object. An imaging system will invariably produce some level of artifact, but it becomes an issue if it obscures an abnormality, resulting in a false negative diagnosis, or mimics an abnormality, giving a false positive result.
Artifacts can be due to patient factors, scanner design factors or the reconstruction process, which by necessity involves some approximations.

Doses from CT examinations are generally significantly higher than those for conventional X-ray, although a CT scan provides more diagnostic information. The CT doses may be typically factors of 10s higher for standard head and abdomen examinations, and factors of 100s for chest examinations.

The Importance of Pulse Oximeters

Before the development of pulse oximeters, in the not-so-distant past, physicians primarily had to assess, diagnosis, and evaluate many medical conditions based on their experience and clinical judgment. This is an essential part of diagnosis, but some symptoms manifest only at the later stages of the disease, especially with problems concerning respiration. When breathing is weakened, arterial blood oxygen levels are reduced. Oxygen deprivation is dangerous and puts patients at risk. Fortunately, with the advancement of medical technology, high-quality innovations in the medical field have allowed doctors to diagnose and treat diseases more successfully. As a case in point, the development of the pulse oximeter has decreased the time in detecting oxygen desaturation and has also greatly minimized unnecessary blood testing.

There are many occasions on which a person can be deprived of oxygen. Hypoxemia, where there is a low amount of oxygen in the blood, may be brought about by illness or trauma to breathing structures. People who have respiratory disorders have the greatest chances of developing decreased arterial oxygen saturation. The principal candidates are patients with asthma and chronic obstructive pulmonary disease, and to a lesser extent, cardiac patients. Blood disorders that cause a deficiency in hemoglobin or alter the capacity of hemoglobin to carry and transport oxygen also result into decreased oxygen saturation levels.

The purpose of a pulse oximeter is to read the current amount of oxygen present in blood by placing the sensor over the fingertip (or sometimes the earlobe). The pulse oximeter reading will indicate whether activity needs to be stopped, or if supplemental oxygen is needed. Parents of children who have asthma are often advised to have a pulse oximeter with them, especially during strenuous activity. If the pulse oximeter results are read as low, then the child must stop playing, and take necessary medications.

For the elderly population, a pulse oximeter is also an important item. Heart disease leading to oxygen deficiency is a common cause of mortality among the geriatric population, so the pulse oximeter has become standard equipment in nursing homes. The hand-held pulse oximeter has proven to be useful in getting a non-invasive, yet accurate and continuous reading.

If delayed, oxygen deficiency causes brain damage, and can affect other vital organs. This is why airway and breathing is a priority during resuscitation, and a pulse oximeter is always present in ambulances, emergency rooms, operating rooms, or any health care facility. Pulse oximeters are also available for home use.

Medical Imaging Workstations Means More Effectiveness

The medical imaging workstation is situated in the field of information technology and has become an essential device in the clinical workflow of radiology departments. The images produced by digital x-ray computed radiography, direct digital radiography, computed tomography (CT) scanner, magnetic resonance imaging (MRI) scanner, ultrasound or any of the other digital imaging tools are stored in the medical imaging’s workstation’s PACS (or picture archiving and communication system), and then may be retrieved, viewed and worked on, according to need.

The medical imaging workstation system was created in order to provide more economical and efficient storage of images, while giving quick access to rapid image retrieval, reports from multiple modalities and concurrent access from several different workstations at the same time. A PACS medical imaging workstation consists of four main mechanisms: imaging modalities such as CT and MRI, a protected system for the transmission of patient information, workstations for interpreting and reviewing images, and archives for the storage and retrieval of images and reports. Combined with already obtainable, as well as up-and-coming internet technology, PACS has the capability of distributing efficient, quick access to images, interpretations, and related data. PACS breaks down the physical and time barriers associated with traditional film-based image retrieval, distribution, and display, saving medical facilities both time and money.

In the past, before the existence of medical imaging workstations, everything had to be printed out on paper and film imaging necessitated expensive, toxic chemicals. In addition, thousands of patient records had to be stores in a hard copy format, which had to be organized and weren’t easy to access. Since PACS and other types of medical imaging workstations have been developed, medical facility efficiency has greatly improved, the time wasted on routine tasks has decreased and most importantly, the focus on caring for the patient has become easier as many tasks are automated.

This means that physicians and technicians consulting on a patient’s case can easily view the same images and communicate with each other. Most medical imaging workstations allow you to sort through thousands of digital images and work with the ones you want, while sharing them with others both onsite and offsite. Daily work can be backed-up and automatically and information from multiple workstations can be stored on a server both onsite and offsite.

Many medical imaging workstations also allow you to add text to digital images. High-resolution display monitors are used to guarantee high-quality presentation of the images, and a color display monitor is also available for use with the radiology information system (RIS), so that color images can be best viewed. The RIS part of the system allows you to schedule patients, order tests, and write reports, upgrading your radiology department for the ultimate in efficiency.

Obstetric Ultrasound Scanners Explained

Obstetric ultrasound scanning is an ultrasound imaging method designed to be used to augment physical examinations in the course of prenatal care. There are a large variety of uses for obstetric ultrasound, and this procedure has become a routine part of prenatal care for many women, especially women throughout Europe and North America. It has become quite common for parents to request print-outs of the images of their growing infant and the technician frequently prints out pictures for them to see and explains the fetus’s configuration as seen on screen to the parents, during the course of the obstetric ultrasound scan.

In obstetric ultrasound imaging, high-frequency sound waves are bounced off the body to create an accurate image of the inside of the uterus. Very high frequency sound waves of between 3.5 to 7.0 megahertz (3.5 to 7 million cycles per second) are normally used for this purpose. This is achieved by using a transducer which emanates waves and generates an image based on the length of the response time and the changes in frequency. The obstetric ultrasound results created can be either a still or moving image, with advanced technology being implemented to create three-dimensional ultrasound images which provide even more specific details. The obstetric ultrasound image may be acquired by covering the woman’s abdomen in a conductive gel and running the transducer along the belly, or by inserting the transducer into the vaginal canal to get a clearer image, which is known as a transvaginal ultrasound. The resulting image gives a picture of the uterus and its contents, along with adjacent body structures. These measurements outline the foundation in the assessment of gestational age, size and growth in the fetus. A full bladder is often compulsory for the procedure when abdominal scanning is done in the early stages of pregnancy. There may be some discomfort from pressure on the full bladder.

There are a wide variety of uses for obstetric ultrasound. Obstetric ultrasound imaging is customarily used to evaluate a pregnancy. This may include determining how far along the pregnancy is and confirming that the fetus is developing normally. Movements such as fetal heart beat and abnormalities in the fetus can be appraised and measurements can be made accurately based on the images displayed on the monitor. An ultrasound can also be used specifically to check for fetal malformations or problems, including a detached placenta. If a mother comes with pregnancy complications indicating fetal distress, obstetric ultrasound may be used as a diagnostic tool to check on the status of the baby without having to use invasive techniques which could jeopardize the pregnancy.

As there are various obstetric applications, different types of obstetric ultrasound probes are required, depending on which is indicated. If an obstetric ultrasound scanner model has fixed probes, then it may only be suitable for a limited subset of applications. For this reason, it is common for ultrasound systems to have interchangeable probes, and they frequently have more than one probe connection socket for the different applications.

Understanding Diffusion MRI

Diffusion MRI is a well-known and widely accepted magnetic resonance imaging (MRI) methodology which generates in vivo images of biological tissues weighted with the local microstructural characteristics of water diffusion, providing an effective way of visualizing functional connectivities in the nervous system. This relatively new and powerful imaging technology gives us further tools to study variations and development of normal brain anatomy, and diagnose disruption to the white matter in neurological disease or psychiatric disorder. Diffusion MRI helps us to better understand the structural organization of the brain through an identification of the neural connectivity patterns with the help of Diffusion Tensor Imaging and High Angular Resolution Diffusion Imaging.

Diffusion-weighted magnetic resonance (MR) imaging, boosted by established successes in clinical neurodiagnostics and powerful new applications for studying the anatomy of the brain in vivo, has been an important area of research in the past decade. Current clinical applications are based on many different types of contrast, such as contrast in relaxation times for T1- or T2-weighted MR imaging, in time of flight for MR angiography, in blood oxygen level dependency for functional MR imaging, and in diffusion for apparent diffusion coefficient (ADC) imaging. Even more highly developed technologies than these are in use today for the study of brain connectivity and neural fiber tract anatomy.

Over the years, increasingly complex data acquisition schemes have been developed, while the theoretical foundations of diffusion MRI have come to be better understood. For the radiologist who wants to use these techniques in clinical practice and research, it is important to understand a few key principles of diffusion MRI, as follows:

A recent advance in MRI known as Diffusion MRI looks at the random motion of water particles in the body. This is particularly interesting when taking images of the brain, because water tends to move more along the directions of the connections inside the brain. These connections in the brain, known as "white matter", are crucial to keeping the brain working correctly. They are the pathways that carry information from one part of the brain to another, and if they are damaged, the brain cannot perform even the most simple tasks. Diffusion MRI is unique in its ability to study these pathways, based on how water flows along them.

There are many diseases that affect the white matter in the brain, and it can be very hard to understand exactly how the disease attacks the white matter, to predict how the disease will develop in a particular person, and to decide what the right treatment is for that person. Fortunately, because diffusion MRI is sensitive to changes in white matter, it is an excellent way of finding out about these diseases. For example, if the disease is breaking down the pathways, water stops moving along them, or leaks out of them, and diffusion MRI pinpoints this for diagnostic purposes.