1Introduction to RadiographsMaking sense of the shadowsBasics of image formation• Radiographs are literal shadows; x-ray photons are generated from a tube (light bulb), “shine” on an object, and strike film behind it• X-ray photons may be absorbed or scattered (reflected), just like visible light• Unlike visible light, x-ray photons can also pass through a patient’s body, giving them the opportunity to be absorbed or scattered by deeper structuresBasics of image formation• Because x-ray photons behave (more or less) like light photons, many of the same rules apply– Magnification– Penumbra (blurring)– Distortion– “Denser” object, deeper “shadow”– Compression of a three dimensional object into a one dimensional imageMagnification/penumbra Magnification/penumbra Density of shadow2Density of shadow DistortionDistortionBasics of image formation• BUT, because x-ray photons pass through tissues, the 3-D →2-D effect is greatly exacerbated.– Shadow puppet—exterior margin– Photograph—facing exterior surface– Radiograph—margins, exterior surface AND interior architectureSuperimposition3Basics of image formation• ALSO, because the medium is (generally) transparent and flat, you can look at an image in a way very different from how it was taken– Cannot tell right from left without anatomic or artificial markers– The shadows can give the impression that you are seeing things as they are in 3D, but you are not– Gravity works (up/down ≠ dorsal/ventral, in most cases)Terminology• When describing structures within the patient, use same terminology as for anatomy (cranial/caudal, dorsal/ventral, medial/lateral, axial/abaxial, proximal/distal, etc)– Remember to use dorsal/palmar or dorsal/plantar for distal limbs– Remember to use rostral/caudal for headTerminology• Avoid the use of terms like “under/over”“behind” “on top” etc.• Opacity is a more appropriate term than “density” because density can mean different things (physical density of objects in patient, optical density of resulting film)• Light/dark also bad, different people have different mental perceptions of these terms4“light” vs “dark” image Terminology• When describing a RADIOGRAPH, “simply”describe the path of the beam as it travels from the tube to the film• In small animals, it is assumed the beam is vertical, coming from above the animal• Examples– Ventrodorsal (VD)– Dorsoventral (DV)– Craniocaudal (CrCa)Terminology• Technically, lateral views of the abdomen/thorax, etc should be described as “right to left lateral”and “left to right lateral”, but convention lets us shorten it to left lateral (patient is in left lateral recumbency) and right lateral (patient is in right lateral recumbency)• Which recumbency the patient is in DOES make a difference for abdomen and thoraxTerminology• Technically, lateral views of the limbs should be described as “lateral to medial” or “medial to lateral”, but convention lets us just call them “laterals” (it is assumed that the limb of interest is down, or against the film in a standing patient)• Which direction the beam is going SELDOM makes a differenceTerminology• Obliques– Can be very simple, and some are very common • Dorsolateral-palmeromedial oblique (DLPMO) of carpusTerminology5Terminology• Technically, should have the angle of obliquity stated in the name of the view (dorsal 60° lateral-palmeromedial oblique), but for standardized views, it’s not needed in everyday conversation.• However, keep in mind that the degree of obliquity makes a big difference in the appearance• Terms such as “lateral oblique” and “medial oblique” mean different things to different people and should be avoidedTerminology• Any “special” positioning of the patient or beam can also be described (right lateral recumbent horizontal beam VD—a.k.a. right decubitus; flexed lateral)• Formal naming can get extremely cumbersome for standard views (e.g. dorsal 30° proximal 35°lateral-palmerodistolateral oblique of the metacarpophalangeal joint). In daily conversation, “DLPMO of the fetlock” is acceptableSo, why do we need oblique views if they’re such a pain?• In the majority of instances, “things”(fractures, pleural fissures, periostealproliferations, etc) are much easier to see if the x-ray beam strikes them in tangent• “Things” are much harder to see (or potentially invisible) if the x-ray beam strikes them head-on (en face)—they get lost in all the other stuffSo, why do we need oblique views if they’re such a pain?• Oblique views are nearly obligatory when imaging complex structures (carpus, tarsus, skull)• Different oblique views may be needed to follow a fissure in its entirety• Oblique views may be needed to highlight “oddball” lesions (e.g. chest wall mass)En face vs. tangentIndications for radiographic examination• To confirm a diagnosis or to aid in ranking a list of differential diagnoses (e.g. twelve year old Poodle with a heart murmur probably has mitral valve disease)• To determine the extent of diagnosed disease and form a prognosis (just how big is his heart, anyway?)• To determine if there are concurrent diseases present (sure, he has mitral disease, but is he coughing because he has bronchitis?)6Indications for radiographic examination• To guide therapeutic choices (is his heart disease compensated? Vessels a little congested? Fulminant heart failure?)• To follow the course of previously diagnosed disease (is our Lasix™working?)• To go on a fishing trip (poodle’s owner says “He’s just not himself”)Indications for radiographic examination• ALWAYS ask yourself the question: “Will the results of this diagnostic test potentially change what I (or the owner) do with the patient?”Selection of imaging procedure• Choices are:– Standard radiographs– “Special procedures”—positive or negative contrast agent added to part(s) of patient, fluoroscopy, etc– Ultrasound– Computed Tomography (aka CT or CAT scan)– Magnetic Resonance Imaging (MRI)– Nuclear Scintigraphy Selection of imaging procedure• Keep in mind that most of our procedures depict a “moment in time”—just because something was normal on radiographs yesterday does not mean it is still normal todaySelection of imaging procedure• Standard Radiography—Advantages – Fast, relatively inexpensive, widely