Body Organization, Planes, Habitus, and Positional Terminology
Unit 1: Anatomy, Positioning, and Medical Language. Lesson 1 of 60 in CRES Academy.
Service calls in radiology arrive in the radiographer's language: the table will not reach the lateral decubitus detent, the tube column cannot clear a hypersthenic patient, the manual says to level the detector to the midcoronal plane. You will never position a patient, but you cannot move the equipment to the right place until you know what those words mean. This is the medical terminology half of the first domain: the words for parts, planes, directions, and positions that a requisition, a protocol, and a service manual all assume you already own.
From cells to systems
Cells are the smallest living units. Cells of one kind form tissues: epithelial (linings), connective (support), muscle, and nervous. Tissues build organs such as the heart, lungs, liver, and kidneys, and organs that work together form systems: circulatory, respiratory, gastrointestinal, urinary, musculoskeletal, nervous, endocrine, and lymphatic. Every room in the department exists to image one of those systems, and that is the depth the exam asks for.
The planes the equipment is aligned to
- Sagittal planes divide the body vertically into left and right parts. The midsagittal plane, also called the median plane or the median sagittal plane, divides it into equal halves, and it is the line a tube column, table centerline, and laser aimer are set to.
- Coronal planes divide the body vertically into front and back parts; the midcoronal plane runs through the middle of that split and is the reference a manual uses for detector height.
- Transverse planes, also called axial planes, cut horizontally into upper and lower parts. Cross-sectional systems reconstruct in this plane, which is why a computed tomography service manual talks about axial slices and table increments.
Directions and patient positions
anterior / posterior front / back the sternum is anterior, the spine posterior superior / inferior toward head / toward feet the lungs are superior to the liver medial / lateral toward / away from midline the sternum is medial, the ribs lateral proximal / distal near / far from the trunk the knee is proximal to the ankle cephalic / caudal toward head / toward feet tube angles are named this way cranial / caudal toward skull / toward tail the same pair used of anatomy supine / prone face up / face down bedside work is mostly supine erect / recumbent upright / lying down chest work is erect when the patient can stand
A decubitus position means the patient is lying down and the beam runs horizontally, which is how free air and fluid levels show. Lateral decubitus is lying on a side, named for the side that is down. Dorsal decubitus is on the back and ventral decubitus is face down, both with the beam crossing side to side. Recumbent positions without the horizontal beam are named the same way: dorsal recumbent is on the back, ventral recumbent is face down, and left lateral recumbent or right lateral recumbent is on the named side, so a left or right lateral decubitus is simply that position with the beam turned horizontal. To the equipment that means a horizontal tube, a vertical detector, and locks that actually hold.
Body habitus
Build decides where the organs sit, so it decides where the beam is centered and how much exposure the part needs.
Hypersthenic about 5 percent massive, broad deep midsection; high diaphragm, high transverse
stomach, high outside gallbladder, colon framing the abdomen; most exposure
Sthenic about 50 percent the average athletic build technique charts are written for
Hyposthenic about 35 percent more slender than sthenic; stomach and gallbladder sit high
Asthenic about 10 percent frail, long shallow narrow midsection; heart nearly vertical at the
midline, low medial stomach, low midline gallbladder, low colon; least exposureBetween the extremes those organs move 6 to 8 inches, which is more than the collimated field of many exams. That is why a complaint of "the centering is off on big patients" is usually technique and not a broken detent.
Body Organization, Planes, Habitus, and Positional Terminology, explained slowly
Why a service technician learns positioning words
You are not going to position anyone. But nearly every complaint that reaches you has been translated once already, from what the radiographer saw into words, and if you cannot read those words you will chase the wrong part. "I can't get a cross-table lateral on this patient" is a horizontal-beam and detector-height problem. "The decubitus lock lets go" is a brake. "The lasers do not line up with the midsagittal plane" is an alignment procedure. Learn the vocabulary once and every call afterward arrives already half diagnosed.
The three planes, and the equipment each one belongs to
Plane Divides the body into Where it shows up in service Sagittal left and right parts table centerline, laser aimers, tube column travel Midsagittal (median) equal left and right halves the alignment reference for almost every setup Coronal (frontal) front and back parts detector height, lateral centering Midcoronal the middle of front and back the reference a manual gives for a lateral Transverse (axial) upper and lower parts cross-sectional slices, table increment, slice width
Say the level with a transverse plane, because there is an infinite number of them: a transverse plane at the xiphoid is a different place from one at the navel.
Direction words, with the test the exam uses
Anatomical position is standing, facing you, palms forward, and every direction word is relative to it.
anterior front posterior back superior toward the head inferior toward the feet medial toward the midline lateral away from the midline proximal nearer the trunk distal farther from it supine face up prone face down erect upright recumbent lying down in any position
The pairs are always relative: the knee is distal to the hip and proximal to the ankle at the same time. Exam items exploit that, so read which structure is the reference.
Decubitus, the position that is really an equipment requirement
A decubitus position is defined by the beam, not the patient: the patient lies down and the central ray is horizontal. That is what makes free air rise to a visible edge and fluid settle to a level. Lateral decubitus is on a side and is named for the down side, so a left lateral decubitus has the left side against the table. Dorsal decubitus is on the back and ventral decubitus is face down, both with the beam crossing side to side. All three need the same three things from you: a tube that locks in a true horizontal position, a detector that stands vertically and holds its height, and a table or stretcher lock that does not creep. A "decubitus views look tilted" complaint is a level and lock complaint.
Habitus and the centering argument
Habitus Share Organ placement Exposure
Hypersthenic 5% high diaphragm, high transverse stomach, most
high outside gallbladder, colon framing
Sthenic 50% the average build charts are written for the baseline
Hyposthenic 35% stomach and gallbladder high, slimmer trunk less than sthenic
Asthenic 10% heart nearly vertical at the midline, low least
medial stomach, low midline gallbladderBetween hypersthenic and asthenic those organs move 6 to 8 inches. That is larger than the collimated field for a gallbladder or a stomach study, which is why centering by habitus is a radiographer skill and not a machine setting, and why "we always miss the gallbladder on big patients in room 3" is almost never a broken detent. Check the lamp, the light field accuracy, and the distance indicator, prove them, and hand the rest back as technique.
What to memorize
- Cells, tissues, organs, systems. Sagittal left and right, coronal front and back, transverse or axial top and bottom.
- Anterior, posterior, superior, inferior, medial, lateral, proximal, distal; supine, prone, erect, recumbent.
- Decubitus means lying down with a horizontal beam; lateral decubitus is named for the down side; dorsal is on the back and ventral is face down.
- Habitus 5, 50, 35, 10 percent for hypersthenic, sthenic, hyposthenic, asthenic, with 6 to 8 inches of organ movement between the extremes.