Radiographic Projections & Positioning Guide: Imaging Procedures

PREFACE

From the moment x-rays were discovered in 1895, their incredible power to see inside the human body was undeniable. Imagine being able to look inside the human body without taking out a scalpel!

Over the years, the ways we capture, develop, display, and store these images have evolved drastically. Yet, there's one thing that hasn't changed much: how we position patients for these life-saving images of the inside of our bodies.

Despite the rise of advanced imaging technologies such as CT, ultrasound, and MR, the classic x-ray image remains a go-to in an emergency to quickly visualize bones and inner organs on a two-dimensional image. General radiography is often the frontline hero in medical diagnostics. But here's the caveat: getting that  perfect x-ray is not just about pointing and clicking. It demands precise positioning skills that make this career both challenging and incredibly rewarding.

Poor positioning or image quality can send doctors hunting for alternative imaging methods and reducing the value of the profession. It shouldn't be that way. Accurate positioning is crucial. In trauma situations, or if the patient cannot move, it is the responsibility of the radiographer to manipulate the central ray and the detector to produce an accurate representation of the part. A high-quality image relies on the radiographer’s expertise.

Besides positioning knowledge, communication is key. Whether dealing with trauma patients, those who are mentally challenged, anxious patients, or kids, the radiographer's verbal skills can make a world of difference. And every radiographer must remember to use radiation cautiously, following the ALARA principle (As Low As Reasonably Achievable).

This positioning and procedure guide is a treasure-trove for educators, students, recent graduates, and experienced radiographers. It covers everything positioning related, from patient care, infection control and technical factors, with a focus on digital technology.

Also available is a companion book on fluoroscopy studies that’s packed with detailed procedures and images.

Remember: Success is not a one-time action. It's a continuous process that takes time, effort and dedication.

Kudo to all imaging radiographers saving lives with quality imaging and patient care!

ACKNOWLEDGMENT

Thanks to my husband, family and friends for their help and support.

It is with pleasure that I recognize the contributions from many of the graduates and friend of the Stamford Radiology Program. Their modeling help with the original edition was invaluable. These include Kari Adams, Jennifer Ayaso, Yvonne Bijarro, Gregory Parry, George Peart, Jalal Shirazifard and Kevin Smith.

Special thanks to Nupur Chakma, graduate of the Program in Radiology, Fortis College – Landover, class of 2021 ̶  cohort 2. Her timely suggestions and editing were greatly appreciated.

I also wish to acknowledge the help I received from the current students and graduates of Fortis College-Landover radiologic technology program. These willing and understanding models were Fransesco Bonilla, Lise Bosquet, Edna Brizuela, Keiry Castellon, Brittney Cooper, Ena Davis, Brian Dye, Kelly Fuentes and Hector Anderson Ortiz.

Radiographic Policies and Procedures

Importance of Standard Precautions

Radiographic imaging must always be performed using standard precautions and the proper infection control techniques as outlined by the Centers for Disease Control and Prevention (CDC) and the Hospital Infection Control Practices Advisory Committee (HICPAC). Standard Precautions incorporates fluid and body precautions and body substance isolation. Standard Precautions are required whenever there is a possibility of contact with blood, body fluids, secretions, excretions, mucous membranes and nonintact skin. Standard Precautions must be applied to all patients.

Hand washing

Washing hands is a basic infection control technique. Washing hands and cleaning all areas of the x-ray table, erect stand and detectors before and after contact with the patient. Hand washing must take place even if gloves are worn.

Asepsis  means the state of being free from germs. There are two types:

Surgical asepsis- also referred to as a sterile technique, is the elimination of pathogens by sterilization.

Sterilization destroys microorganisms and their spores.

Sterilization is the absolute killing of all life forms.

Sterilization can be accomplished by autoclave (steam) gas, radiation or chemicals.

Sterility is an absolute state. - An object is either sterile or not.

Medical asepsis- also called clean technique.

Used to limit the number and prevent the spread of infectious microorganisms.

Microbes are not eliminated, just reduced or their environment altered so it is nonconductive to growth and reproduction.

Specific Transmission-Based Precautions applied whenever a patient is infected with a pathogenic organism or a communicable disease, also for patients at risk for infections (immunosuppressed).

Airborne Precautions

Organisms remain suspended in the air for extended periods of time e.g., tuberculosis (TB).

Infected patients are placed in a negative-pressure isolation room with the door closed.

Healthcare providers should wear respiratory protection (filtered mask) on entering a patient’s room.

Patient leaving the room must wear a surgical mask.

Droplet Precautions

Pathogens spread through large droplets expelled when patient coughs, sneezes or talks. Droplets travel about 3 feet (91.5 cm) and infection occurs through contact with mouth, nasal mucosa or conjunctiva.

Patients are placed in private rooms with doors closed.

Healthcare provider should wear a mask within 3 feet (91.5cm) of patient.

Patient should wear mask on leaving the room.

Contact Precautions

Infections spread through direct contact with patient or a contaminated object (formite) e.g., bed rails.

Clean all contaminated equipment after leaving room.

Health care providers should wear gloves and wash hands before entering and after leaving the room.

Impervious gown needed only if contact with patient is possible, and a face mask is suggested to avoid contaminating the nasal mucosa.

Patients leaving the room should wear an impervious gown and face mask.

Removing contaminated PPE

Remove in this order:

1) gloves, 2) gown, 3) mask 4) wash hands. 

Clinical History Documentation

Reasons for documentation:

Aids in diagnosis and prevents misdiagnosis

To transfer critical information to the radiologist who may never see the patient. The technologist can locate the injury site or foreign body markers be used to indicate location of a penetrating injury.

Allow modification of exposure

Documentation of additive versus destructive pathologies or the presence of a prostatic device which could require changes in the normal technical factors.

Rule out errors

Document site or type of injury to avoid imaging the wrong body part. To verify incorrect requisitions poor internal preparation, allergies or preexisting medical history.

Necessary for legal coding

Documentation needed to determine the correct diagnostic code – needed for medical research, billing and insurance reimbursement.

Patient Communication

Communicating specific breathing instructions is important in controlling motion. Patient motion control is critical to producing a high-quality radiograph.

Involuntary motion

Best controlled by using short exposure times. This is  outside of a patient's control e.g., peristalsis.

Voluntary motion

Best control by communicating instructions clearly, by providing the patient with a warm and comfortable imaging experience, by using support devices when necessary and by using immobilization devices as a last resort. E.g., breathing.

Breathing instructions are necessary when imaging the thorax and abdomen but not necessary when imaging the skull or extremities. However, even when breathing instruction is not required for imaging, telling a child or anxious adult to stop breathing during an exposure can aid in keeping them still.

Radiation Safety

Minimize repeats–Accurate positioning to avoid repeats.

Close collimation– Used to reduces patient dose and improves radiographic quality, especially in digital imaging.

Protective Shielding,  if warranted– Limited used in digital. It should be used especially when imaging children and pregnant patients. Shielding should not compromise the image and must never be included in the collimated field. Shielding could be  used whenever the gonads are within 5cm or 2 inches of the collimated field.

The 10-day or LMP (last menstrual period) rule–Radiological examinations involving the pelvis or lower abdomen of female patients. Schedule imaging during the first 10 days following the onset of menstruation. The rule is abandoned if imaging is medically necessary.

Avoid imaging the fetus especially during the first trimester unless medically necessary.

Selection of correct exposure factors–Best practice is the use of high kV and low mAs to reduce patient dose. Use the 15% rule to reduce the mAs while increasing the kVp thus reducing patient dose without affecting image quality.

The 15% Rule

A 15% increase in kVp of 15% =  doubling the mAs.

Increase factors: increase the kVp by 15% and reduce the mAs by ½.

Decrease factors: reduce the mAs by ½ and increase the kVp by 15%.

Patient positioning–The posteroanterior projection (PA) versus the posteroanterior (AP) will allow reduced radiation to the eyes, breast, thyroids and often the gonads.

Personnel protection–Provide lead aprons, thyroid shielding or lead gloves as needed, to all personnel in the x-ray room during an exposure. Doubling your distance from the source of radiation will reduce exposure by ¼.

ALARA–As Low As Reasonably Achievable. Must be practiced by all radiographers. Always practice time, distance and shielding.

Units of Radiation

Graya (Gya ) - old units: Roentgen (R), coulomb/kilogram (C/kg)

Measures radiation exposure in air.

Grayt (Gyt) - old unit: Rad (rad)

Measures the amount of radiation energy absorbed in a medium e.g., body tissue.

Sievert (Sv)  - old unit: Rem (rem)

Measures the occupational exposure or dose equivalent–consideration given to the biological effects of the various types of radiation.

Skin Entrance Exposure (SEE)

Measure the exposure to the skin in the region where the radiation first strikes the body.

Effective Dose

Consider the dose to all the organs and their relative risk of becoming cancerous or the risks of genetic damage to the gonad.

Source to skin distance (SSD)

–critical in fluoroscopy imaging

38 cm (15 inches) minimum for stationary fluoroscopy units.

30 cm (12 inches) minimum for mobile fluoroscopy (C-arm).

Somatic effects–Radiation affecting the individual only.

Genetic effects–Radiation affecting future generations of the individual.

Deterministic effects (nonstochastic) effects - High radiation doses produce an initial response.

Stochastic effects (probabilistic effects) - Low doses delivered over an extended period with a late or delayed response.

Terminology and Definitions

Cassettes: lightproof devices that hold the film in analog imaging. This terminology is often incorrectly used when referring to the image plate or detector in digital imaging.

Films: used to acquire the image, display the image and archive the image in analog imaging.

Image Plate (IP): (incorrectly referred to as cassettes): holds the photostimulable phosphor (PSP) in systems called PSP or computed radiography (CR) imaging.

Photostimulable phosphor (PSP) or Storage phosphor screen (SPS): contained within the IP. The PSP receives the energy of the x-ray beam. The acquired image is processed and displayed on a computer monitor.

Image Receptor (IR): received the energy of the x-ray beam. It can be a detector or PSP.

Detector: a specialized device that acquires the image in digital flat panel systems (DR) also called Thin Film Transistor (TFT) imaging systems.

Pixel, or picture element: the smallest element in a digital image.

Matrix (Image matrix):  is made up of individual picture elements(pixels), each designated by its column and row number.

Cells in the matrix are pixels with numeric values arranged in rows and columns.

Detector elements (DELs or dexels): located within rows and columns on the TFT in the digital system.

The size of the Del can affect the spatial resolution of the system.

Dynamic Range:  the number of gray shades with which each pixel can be represented by the system.

Exposure latitude: the range of underexposure or overexposure that can occur while still producing an acceptable image.

Analog receptors can correct for:

30% underexposure to 50% overexposure.

Digital receptors can correct for:

50% underexposure to 400% overexposure.

The Anode Heel Effect

The reduction in intensity of the x-ray beam at the anode end of the tube.

Minimizing anode heel effect involves using shorter SID or placing the thicker body part at the cathode and thinner body part to the anode.

Monitors

The radiologist’s monitor has smaller pixels, superior brightness, and better spatial and contrast resolution than the radiographer’s monitor.

Technical factors

Kilovoltage peak (kVp) is a measure of the energy, the voltage and therefore the penetrating ability of the x-ray beam.

Milliampere per second (mAs).

Milliampere (mA) controls the quantity, intensity or number of electrons produced.

Exposure time in milliseconds (ms) controls the duration of the exposure in milliseconds.

mA multiply by seconds = mAs

Note:

No amount of mAs increase can compensate for insufficient kVp.

The SID is sometimes added when listing the technical factors.

Function of AEC

To terminate the exposure when a pre-selected amount of radiation reaches the detector.

The kVp and mA are set.

AEC determines the time of the exposure and the mAs.

Limitations of AEC

Not for use on small or narrow anatomy. The part should completely cover at least one detector cell

Not ideal when imaging anatomy near the peripheral or too close to the edge of the body.

Should never be used when there is any radiopaque object in the area of interest. This includes surgical apparatus, orthopedic devices or anything metallic.

Exposure index (EI)–The exposure sensitivity or sensitivity (S) number. A numeric value representing the exposure the detector received.

The name varies depending on the manufacturer.

The value can indicate over or under-exposure in the absence of visual cues.

The EI value can be directly or indirectly proportional to the radiation striking the detector.

Controlling factor

Intensity of radiation striking detector.

mAs, kVp, total detector area irradiated and/or objects or part exposed (air versus metal or patient’s anatomy).

Deviation Index (DI)– Indicates the difference between a desired target exposure index and the actual exposure.

DI changes by +1.0 for each +25% (increase in exposure), and by -1.0 for each -20% change.

•  Results are multiplicative, not additive.

•  Each step multiplies the previous amount (not the original amount).

Normal DI ranges from -0.5 to +0.5.

•  DI of +1 is overexposure.

•  DI of -1 is an underexposure.

DI is an international standard used by all manufacturers. DI formula: DI = 10log10 (EI/EIT).

Diagram Description automatically generated SID–The source to image detector distance.

OID–The object to image detector distance.

CR–The central ray of the x-ray photon beam leaving the x-ray tube. The beam diverts from the focal spot to strike any object in its path.

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