After the invention of CT itself and moving from first generation CT to third generation CT the incorporation of slip rings into modern CT is the most import enabler of improved scanning. It has enabled a number of clinical applications which were hypothesized when the Nobel Prize was granted for CT, but not possible until […]
Slip Ring CT pictorial guide [helical, cardiac, perfusion, 4DCT] Read More »
CT (Computed Tomography) scanning can be accomplished with multiple different scan modes which have different characteristics. Axial non-volumetric scanning is how CT began where one (or just a few) slices are acquired during each gantry rotation. Traditional helical scanning (some call spiral) has the advantage of being faster than non volumetric axial scanning and also
LET (Linear Energy Transfer), RBE (Relative Biological Effectiveness) and OER (Oxygen Enhancement Ratio) are important terms in radiation biology and relate to the relative damage that will occur with radiation under different circumstances. As LET increases there are more energetic electrons deposited closely together and thus damage to DNA is more likely. Therefore, even with
LET, RBE and OER (Oh My!). Radiologic Technologists Guide to 3 Radiation Biology Terms. Read More »
Radiation damage can be either acute or chronic depending on the conditions. Acute radiation effects are due to short exposures to radiation at a relatively high dose rates and the impact is observed within days or weeks (examples include acute radiation syndromes). Whereas chronic radiation effects are typically associated with lower doses and the effects
Radiation Carcinogenesis In this post we will describe the stochastic effect of radiation carcinogenesis (a fancy way of saying a higher risk of cancer induction after being exposed to ionizing radiation). The mechanism for carcinogenesis is primarily x-rays coming in, generating energetic electrons which then either directly or indirectly cause DNA damage. The data which
Radiation risks to germline cells (sperm and ova) include reduced fertility, and hereditary risks of increased mutation rate. These effects are dependent on the radiation dose: (males) [0.15-0.5 Gy] reduced sperm count, [0.5-6 Gy] temporary sterility, [greater 6 Gy] permanent sterility, and (females) [2-12 Gy depending on age] causes permanent sterility. Hereditary risks of increased
The acute radiation syndromes are cause by a sudden large dose of radiation to the body and depending upon the dose level one will experience either: Cerebral Vascular (a.k.a. CNS) Syndrome, Gastrointestinal (GI) syndrome, or hematopoietic (bone marrow) syndrome. This listed order is the order of severity and of the higher dose levels lead to
Acute Radiation Syndromes [ Hematopoietic, GI, CNS ] for Radiologic Technologists Read More »
Cataracts are formed when cells are damaged or die in the lens of the eye. The dose level which leads to cataract induction depends on the dose fractionization, ie. how many weeks/months was the dose delivered. The radiation dose which has been shown to cause cataract is between 2mGy (single fraction) -5.5 mGy (dose distributed
Cataract Induction from X-ray Radiation (Illustrations, Dose levels) Read More »
The Contrast to Noise Ratio (CNR) in a medical image is a measure of the contrast between the tissue of interest and the background (i.e. the neighboring tissue). The Signal to Noise Ratio (SNR) is a measure of the image signal in a given region to the background. The ability to visualize objects in a
The spatial resolution of an x-ray or CT system is a measure of how the ability of a system to differentiate small structures. If you imagine imaging a very small point like object an image of that object is called the Point Spread Function (PSF). When this function is radially averaged the Line Spread Function
X- ray Resolution (PSF, MTF, NPS, DQE) for radiologic technologists Read More »
