Conventional Radiographic Procedures
The past 2 decades have witnessed extraordinary advances in medical imaging, but conventional radiographic procedures remain the keystone in diagnosing musculoskeletal disorders. With rare exception, plain radiography should be the first imaging study performed in working up musculoskeletal problems. The plain film may lead to a definitive diagnosis, with no other radiologic test required. If not, the conventional radiographic findings are essential for planning subsequent imaging studies. Additional imaging modalities may better delineate the extent and aggressiveness of musculoskeletal disease, but before biopsy most bone diseases have been and continue to be identified from characteristic plain film findings.
Approach to Interpreting Pediatric Orthopaedic Films
An adequate knowledge of the pediatric skeletal system is the most important factor in interpreting pediatric orthopaedic films. In general, pediatric orthopaedists have a proficient knowledge of this organ system, which dramatically changes from birth to approximately 20 years of life. However, there are additional factors not always used by orthopaedic surgeons that help enhance the interpretation of pediatric orthopaedic radiographs. A discussion of these guidelines follows.
Viewing Conditions
The room in which radiographs are viewed should be as dimly illuminated as possible. Visual acuity markedly improves as the ambient light is decreased. Subtle bony and soft tissue changes can be missed if this simple rule is not followed.
Impact of Clinical History on Film Interpretation
If possible, pertinent clinical information should be known before the examiner views the pediatric patient’s radiographs. Knowledge of the patient’s age, gender, race, and symptoms facilitates a more accurate diagnosis.
Age
Age is one of the most important parts of the clinical history because many pediatric skeletal disorders, or manifestations of a particular disorder, occur only within certain age ranges. The patient’s age in combination with the skeletal findings often leads to a diagnosis or helps to limit the differential diagnosis. The patient’s age should be viewable on all images but if it is not, every effort should be made to obtain the patient’s age before a final radiographic diagnosis is made.
Gender
Knowing the patient’s gender also proves helpful in many cases. For example, skeletal maturation occurs on different time lines in male and female pediatric populations. Also, knowledge of the patient’s gender can help the clinician include or exclude certain X-linked disorders, such as spondyloepiphyseal dysplasia tarda.
Race
The patient’s race is often less helpful in the diagnosis than age and gender, yet it may occasionally be useful. For example, certain tropical populations tend to walk earlier than those in more temperate areas and have a higher incidence of infantile Blount disease. Knowing that the young patient is black may be helpful in grouping multiple radiographic findings relating to sickle cell disease.
Signs and Symptoms
Different disease processes may produce similar bony radiographic changes and without knowledge of the patient’s signs and symptoms, a definite diagnosis cannot always be determined. For example, Ewing sarcoma and osteomyelitis may be indistinguishable radiographically.
Avoiding Tunnel Vision
Optimally, the radiographs should be viewed in a room with little ambient light and interpreted in the context of the patient’s clinical history. With or without these requisites, however, the entire image, not just the area of interest or of obvious pathologic involvement, should be scrutinized. Using some type of patterned search encourages the interpreter to analyze all parts of the image, including an examination of the soft tissues, all organ systems included in the radiographic study, and the portion of the skeletal system not obviously involved by a pathologic process.
Examination of the Soft Tissues
Examination of the soft tissues may direct the interpreter to evaluate or reevaluate an adjacent osseous structure that at first glance appears normal. For example, detecting soft tissue edema or a joint effusion should direct the examiner to look for a subtle fracture that is not immediately recognizable. In addition, the soft tissues should be scrutinized for masses, calcifications, and foreign bodies.
Examination of All Organ Systems Included in the Radiographic Study
For example, after the evaluation of the spine on a scoliosis film, the radiographic interpreter should undertake a systematic pattern search of the remaining areas included on the image. A head to toe search first directs the observer to the lung fields for evaluation of intrinsic lung disease and for evaluation of bowel above the diaphragm (e.g., hiatal, paraesophageal, Morgagni, or posttraumatic hernia), which should be identified before surgery. Mediastinal lymph node involvement may represent primary tuberculosis, lymphoma, Castleman disease, or sarcoidosis. Then the abdomen is evaluated for abnormal bowel gas patterns and abnormal intraabdominal calcifications such as appendicoliths, gallstones, urinary calculi, hepatic and splenic calcification, ovarian calcifications (most commonly teratomas), calcification in the scrotal sac (meconium peritonitis or testicular teratoma), and psoas abscess calcification. A last look at the pelvic region should include scrutiny of the presacral region because fetal skeletal parts may rarely be detected if the patient is pregnant.
Evaluation of the Skeletal System Not Obviously Involved by a Pathologic Process
A frequent cause of hip pain in the overweight adolescent is a slipped capital femoral epiphysis (SCFE). Most cases of SCFE are idiopathic but the entire pelvis should be scrutinized for rare causes, such as primary hyperparathyroidism (very rare in children) ( Fig. 10-1 ), secondary hyperparathyroidism associated with chronic renal failure, or vitamin D–deficient rickets. Also, 10% of patients with pseudohypoparathyroidism have associated hyperparathyroidism and may develop SCFE. In all these patients, subperiosteal, endosteal, subcortical, and subchondral resorption may occur. An underlying cause of SCFE may be missed if the entire film is not evaluated.
Importance of Previous Studies
The importance of comparing the current radiographic study with previous studies cannot be overemphasized. There are three main reasons to conduct such a comparison. First, a slowly enlarging lesion may not be recognized as significant unless all previous studies are viewed together in chronologic sequence. Subtle changes in the size of any lesion may be appreciated only when all previous examinations are compared with the current study.
Second, a subtle lesion that is not detectable on a current radiograph may become obvious when the current study is compared with an older study that may demonstrate the lesion more clearly because of a different projection or technique. For example, radiographs of an adolescent’s lumbosacral spine are submitted along with a history of pain and a request to evaluate for spondylolysis. The current study does not clearly delineate a pars intraarticularis defect but on review of the previous lateral scoliosis film, the examiner identifies a definite spondylolysis. More often than any radiographic examiner likes to admit, the answer is on an old study, already in the radiograph jacket or in the electronic file.
Third, if older studies are not reviewed in their entirety when bone dysplasia is considered, a correct diagnosis may be delayed or never made. Many bone dysplasias have similar or indistinguishable appearances during various stages of their development. For example, the radiographic appearances of spondyloepiphyseal dysplasia congenita and Strudwick spondyloepimetaphyseal dysplasia are indistinguishable in the early years of life. In the past, Morquio syndrome was confused with Koslowski spondylometaphyseal dysplasia during certain stages of its development. The overlapping radiographic appearances of many bone dysplasias direct the examiner to observe the patient’s radiographic findings closely over time to make a correct diagnosis.
A final caveat concerning previous radiographic studies—expert witnesses always review the entire case. It is important for practitioners to do the same.
When Plain Films Stand Alone
Plain radiography may be the only imaging modality needed for diagnosis. It is the only study needed to assess many fractures, evaluate bone age, diagnose bone dysplasias, and identify normal variants. The first three topics are discussed in other chapters. This section addresses some of the more common roentgenographic variants of normal.
The reader is referred to Atlas of Normal Roentgen Variants That May Simulate Disease (9th edition, 2012), by Theodore E. Keats, for an exhaustive review of the subject. This radiographic atlas shows the appearance of normal variants in all organ systems from infancy through adulthood. Using this atlas when unusual bony findings are encountered helps the practitioner determine whether the osseous structure in question is a normal variant and thus may help avoid further imaging studies. If this or another atlas of normal variants is not available, the contralateral structure may be imaged for comparison. For example, if the same peculiar bone is present in both feet, it is almost always a normal variant. Rarely, normal variants may be involved by traumatic, infectious, or neoplastic changes. The patient’s history and clinical findings then help determine the subsequent imaging studies needed, if any.
Normal Radiographic Variants of the Immature Skeleton
Synchondroses Commonly Mistaken for Fractures
Sphenoid Bone Synchondroses.
An infant is born with three synchondroses of the sphenoid bone. The frontosphenoid synchondrosis and intersphenoid synchondrosis close by several months to 1 year of life. The spheno-occipital synchondrosis, however, may remain patent until early adulthood ( Fig. 10-2 ). These synchondroses generally are not attended to by the orthopaedic surgeon except when assessing the cervical spine for trauma. The most common question then asked is, “Do these synchondroses represent basilar skull fractures?” Knowing the existence of these synchondroses and when they close eliminates the need to perform other time-intensive and expensive studies.
Body of C2 and Odontoid Synchondrosis.
The synchondrosis between the odontoid and body of C2 may simulate a fracture from birth until it closes, between ages 3 and 7 years (see Fig. 10-2 ). When it is partially fused it may appear as an incomplete fracture of the odontoid. Assessment of the odontoid’s alignment with the body of C2 then becomes extremely important. If the alignment is not anatomic, further evaluation with computed tomography (CT) or magnetic resonance imaging (MRI) is indicated.
Synchondroses Between Vertebral Bodies and Neural Arches.
These synchondroses appear as lucent lines between the vertebral bodies and neural arches from birth until midchildhood, when they usually close (see Fig. 10-2 ). They become particularly noticeable on oblique views of the infant’s cervical spine and may mimic fractures. Reference to Keats’ and Anderson’s atlas is reassuring and instructive.
Ischiopubic Synchondrosis
The ischiopubic synchondroses, which is commonly confused with infection or neoplastic change, may have irregular mineralization and may be asymmetrically expanded ( Fig. 10-3 ). The asymmetry is unusual because most normal variants tend to be symmetric. Complete bilateral ossification occurs as early as age 4 years or as late as 14 years. Pain and tenderness may be associated with an irregularly mineralized and expanded ischiopubic synchondrosis, but without positive laboratory findings further workup is unnecessary. A biopsy of this synchondrosis should not be obtained because false-positive results for neoplastic changes frequently occur. Not uncommonly, however, osteomyelitis may involve the ischiopubic synchondrosis, with positive blood cultures, elevated erythrocyte sedimentation rates, or increased C-reactive protein levels confirming the diagnosis. With adequate antibiotic therapy, the prognosis is good.
Normal Bony Variants Frequently Confused With Pathologic Changes
Osteosclerosis of the Newborn.
A neonate’s long bones may appear very dense, which can be mistaken for pathologic conditions such as osteopetrosis ( Fig. 10-4 ). In general, however, significant clinical findings are associated with pathologic osteosclerotic conditions. For example, jaundice, hepatosplenomegaly, anemia, and pancytopenia are associated with osteopetrosis manifesting in the newborn period. Normal osteosclerosis of the newborn has no associated signs or symptoms and resolves several weeks after birth.
Physiologic Periosteal New Bone Formation of the Newborn.
Physiologic periosteal new bone is not present before 1 month of life and is usually noted between 1 and 6 months of life. It is almost always bilateral and symmetric, involving the femur, humerus, and tibia most frequently. The periosteal new bone formation is thin and separated by a lucent line from the diaphyseal cortex ( Fig. 10-5 ). The patient’s age, bilateral symmetry, and benign radiographic image differentiate this condition from pathologic entities such as trauma, congenital syphilis, osteomyelitis, prostaglandin therapy, infantile cortical hyperostosis (Caffey disease), leukemia, and metastatic neuroblastoma.
Cervical Spine Pseudosubluxation.
Because of ligamentous laxity and horizontally positioned facet joints, the upper cervical spine in infants and children may appear to subluxate during flexion. When multiple cervical vertebral bodies are involved, physiologic subluxation is clearly the diagnosis. Subluxation limited to C2 on C3, however, may be physiologic or associated with a hangman’s fracture. To differentiate these conditions, Swischuk has devised the posterior cervical line. This line is drawn from the anterior cortex of the C1 posterior ring to the anterior cortex of the spinous process of C3 ( Fig. 10-6 ). If the line misses the anterior cortex of the spinous process of C2 by more than 2 mm, a true dislocation is present. This line should be used only to assess C2-3 subluxation.
Dense Transverse Metaphyseal Lines.
Normal children have dense transverse metaphyseal lines, especially between 2 and 6 years of age, that may be confused with radiodense metaphyseal bands associated with lead poisoning ( Fig. 10-7 ). Two radiographic findings, however, may help distinguish normal radiodense metaphyseal lines from those seen in lead poisoning :
- 1.
Normal dense metaphyseal lines are no denser than the metaphyseal or diaphyseal bony cortex, whereas the dense metaphyseal bands associated with lead poisoning are usually denser than the metaphyseal or diaphyseal bony cortex.
- 2.
A dense metaphyseal line commonly involves the proximal fibula with lead poisoning, but the proximal fibula is usually not involved in the normal patient with dense metaphyseal lines.
Lead poisoning, however, cannot be definitively diagnosed from radiographic findings; chemical tests of blood and urine are required.
Avulsive Cortical Irregularity.
An avulsive cortical irregularity usually involves the posterior aspect of the medial femoral condyle, appearing as an irregular and concave defect that may simulate a malignancy ( Fig. 10-8 ). The lesion most probably results from repetitive, avulsion-type trauma. This defect is most frequently seen in 10- to 15-year-olds, is more common in boys, and is often bilateral. An avulsive cortical irregularity should not be sampled for biopsy because a misdiagnosis of osteosarcoma may be made. A correct diagnosis is determined by knowing the general age ranges and characteristic location and radiographic features of the avulsive cortical defect.
Radiographic Technique
Child-Friendly Radiology Department and Technical Staff
A well-trained technical staff experienced in working with children is essential to running a pediatric radiology department. A technologist who is comfortable in caring for children can allay the child’s and parent’s apprehensions and thereby decrease the time and effort required to obtain optimal radiographs. Pediatric radiology technologists usually allow parents to be present in the examining rooms and even to assist with some studies. This decreases the repeat rate and thus decreases the total radiation dose to the young patient. In addition, the radiology technologist uses radiation-limiting techniques, such as patient immobilization and gonadal and breast shielding. Cheerful uniforms and departmental decors with bright juvenile motifs help distract and calm the child. However, the essential component of a child-friendly department is a skilled technical staff that enjoys caring for children.
Equipment Requisites for X-Ray Production
The basic equipment items necessary to produce a standard radiograph are an x-ray generator, x-ray tube, collimators, grids, cassettes, and screen-film combination ( Fig. 10-9 ). However, with current technologic advances, computed and direct digital radiography are becoming more commonly used for image acquisition. A brief description of each device follows.
X-Ray Generator
An x-ray generator modifies an electrical source of alternating current into high-voltage direct current, which provides energy to an x-ray tube for heating electrons off the cathode filament and accelerating electrons from the cathode filament to the anode target.
X-Ray Tube
An x-ray tube is composed of two metal electrodes, a cathode and anode (target), which are mounted in a glass vacuum tube or metal vacuum casing. When the cathode is heated to more than 2000° C by the filament, current electrons are emitted and propelled to the anode. The speed of the electrons from the cathode to the anode is determined by the x-ray tube potential (kilovolt peak [kVp]).
On striking the anode, 99% or more of the high-velocity electrons contribute their energy to heating the anode. The remaining 1% or less of electrons that collide with the anode produce the x-ray beam used for radiographic production. The higher the energy of the impacting electrons, the more energetic and penetrating is the x-ray beam produced.
Collimators
Collimators reduce scatter radiation that not only degrades the image but delivers unnecessary radiation to the patient. Patient protection is achieved by limiting the x-ray field as much as reasonable. Film quality is improved by decreasing the inherent noise introduced by scatter radiation.
Grids
Grids allow passage of primary radiation and absorption of scatter radiation. They are composed of a series of lead foil strips alternating with x-ray–transparent spaces. The grid ratio is the ratio of the depth of the lead strips to the distance between them. The higher the grid ratio, the less the scatter radiation, but increased primary radiation must be used to penetrate the patient and grid. In small pediatric patients, small irradiated fields produce low scatter levels, which often obviates the use of a grid and thereby significantly decreases the radiation dose. However, patients 5 years of age or older usually require grids for radiographic examinations of the abdomen, pelvis, spine, and skull.
Cassettes
Cassettes are containers for film-screen combinations that produce good screen-film contact. If the contact is good between the screen and film, a dot of light emitted from the screen will produce a corresponding dot on the film. If the contact is poor, the dot of light will diffuse before reaching the film and result in a fuzzy rather than a sharp image.
Luminescent Screen-Film Combinations
Luminescent screens convert x-rays into visible light that exposes the x-ray film and greatly reduces the patient dose because x-ray film is very insensitive to direct x-ray exposure and requires prohibitive patient doses. Since the 1970s, rare earth screens have increased x-ray absorption efficiency and x-ray–to–light conversion efficiency with a resultant decrease in radiation dose of up to 50%. Newer developments, such as computed radiography (CR) and direct radiography (DR), have begun to replace screen-film combinations. These methods are discussed further in the following sections.
Computed Radiography
Storage phosphor CR uses a standard x-ray tube to expose an image on a reusable phosphor image plate. Instead of a screen-film combination, a phosphor plate is placed in the cassette. Basically, the phosphor plate in the cassette is first exposed by x-ray photons, which elevate the phosphor electrons to a high-energy state. The exposed phosphor plate is then placed in a laser image reader in which a laser beam scans the plate, causing electrons to return to their low-energy state and emitting energy in the form of visible light. This light energy is collected and transmitted to a photomultiplier tube that converts light into electrical current and current into voltage. The light intensity is proportional to the voltage, and the voltage variations are converted to a digital signal. An image processor enhances the digital image, which is then sent to a workstation monitor and stored on optical disks, digital tape, compact disks, or a computer’s hard drive.
Advantages of Computed Radiography Over Conventional Radiography
The phosphor image plate responds in a linear fashion to a wide range of exposures, which allows accurate depiction of differences in density. Simply stated, both low-density structures (soft tissues) and high-density structures (bone) may be accurately depicted on the same image. Conventional screen-film systems, on the other hand, have a nonlinear response and narrow range to x-ray exposure. This necessitates that the x-ray technologist use a precise exposure technique to obtain an optimal bone image and a second precise but different exposure technique to obtain an optimal soft tissue image. Overall, film-screen systems have an exposure range on the order of 1000 : 1, whereas the CR plate exposure range is approximately 10,000 : 1. Not only is contrast resolution improved using a CR system, but repeat films caused by exposure errors can almost be eliminated, which decreases the total radiation dose to the patient.
In addition to CR images having greater contrast resolution than conventional plain films, the digital CR images can be further enhanced by computer manipulation before or after transmission to an interactive workstation. These digital CR images, as well as all other digital images (e.g., CT, MRI) can be sent to a picture archiving and communication system and integrated into a radiology information system. This allows rapid retrieval (no lost films) and transmission of digital images and patient information within and between medical centers that are interconnected.
Direct Radiography
Direct radiography, a more recent technologic development, is also becoming a more widely used method of radiographic imaging. Unlike CR systems, which use phosphor imaging plates, DR systems send information from a detector directly to the workstation. The detectors are usually constructed with cesium iodide or amorphous selenium and can be located within the imaging table or wall stand.
Advantages of Direct Radiography
The superior efficiency of the detectors used in flat panel DR produces greater contrast resolution and allows for overall dose reduction for an individual radiographic examination. Spatial resolution, however, is limited by pixel size and is therefore lower than in film-screen combinations. As with CR, there is increased latitude in viewing, with adjustable contrast for an individual exposure. Fewer repeat examinations are required because of the ability to manipulate the image once it has been acquired. Probably the greatest advantage is the cassetteless process that allows higher patient throughput, improving workflow efficiency and patient safety because the technologist is able to remain in the examination room.
Patient Preparation for Radiographic Examinations
Patient and Image Identification
Before a radiographic examination is acquired, the patient’s identification must be checked and reconciled with the radiology requisition. This is usually done by the radiology technologist, who queries the older child or the parents of the younger patient about the patient’s exact identity. Also, the radiology technologist questions the patient or parents about their understanding of the radiographic examination ordered. Needless return visits to the radiology department may be circumvented by asking simple questions, such as “Which side hurts?” or “Which leg did you break?”
An inpatient’s identity must always be verified and checked against the patient’s identification bracelet. If the inpatient is noncommunicative and not accompanied by a family member, nurse, or other medical attendant, and if the radiograph request seems inappropriate to the patient’s diagnosis, the radiology technologist must check the medical chart, if available, or call the nurses’ station for clarification of the request.
The patient’s information—generally the patient’s name, date of birth, medical number, and date of examination—can be printed on conventional film by an identification camera. Patient information for a CR or DR image is entered using a radiology information system, or the radiology technologist types in the patient information during the laser reading.
Proper left and right markers should be placed on each film to help prevent treatment of the wrong anatomic part. This is extremely important if both left and right analogous anatomic structures are deformed and show no differences on visual inspection. At our institution, each image is labeled with left- or right-side markers. Even when three views of the same hand, wrist, or ankle are on one film, each view is labeled with a side marker. This helps ensure proper labeling by forcing the technologist to recheck the side imaged before the next exposure.
Patient Protection
Immobilization
Various immobilization techniques and devices are used to obtain images in the young patient. The radiology technologist instructs the child’s parents that immobilization is necessary to obtain a diagnostic image, prevent physical injury to the patient, and decrease the rate of repeated studies, which limits the radiation dose to the patient. If some explanation of the need for restraining young patients is not given to the patient’s parents, they may regard the procedure as being harmful or abusive to their child.
Shielding of Reproductive Organs
X-rays may cause genetic mutations and chromosomal abnormalities. If genetic mutations develop in reproductive cells, they may not manifest for several generations. To reduce the genetic effects of ionizing radiation, the concept of gonadal shielding was introduced in 1956 by the National Academy of Sciences Committee on Biological Effects of Atomic Radiation.
Gonadal shields are of two basic types: flat contact shields and shadow shields. The flat contact gonadal shields may be made by cutting 1-mm-thick lead vinyl sheeting into various sizes and shapes that are age- and gender-appropriate. These shields are placed on top of the patient or taped to the patient. The gonadal shield is simply positioned over the male patient’s testes ( Fig. 10-10 ). The female contact gonadal shield is placed so that the inferior margin is positioned at the pubis and the upper border extends to below the iliac crests ( Fig. 10-11 ). Shadow shields are made of a radiopaque material attached to the x-ray tube head. The radiology technologist directs the shield to its proper position using a beam-defining light that illuminates the area to be imaged. When an x-ray exposure is made, a shadow of the shield projects over the gonads.
Gonadal shields must be used when the gonads are within 5 cm of the primary beam. For most abdominal and pelvic imaging of the male patient, gonadal shields can be used with no loss of diagnostic information. Shielding of the variably placed intraabdominal ovaries, however, may obscure pertinent information ( Fig. 10-12 ). If two views of a female pelvis are required, one view is obtained with a gonadal shield and the other without the shield. Proper shielding decreases gonadal exposure by 95% in boys and up to 50% in girls.
Shielding of Breast Tissue
X-rays not only are capable of causing genetic and chromosomal abnormalities but they can induce cancer in somatic tissues. At particular risk is maturing female breast tissue, with the rate of breast cancer being appreciably higher after x-ray exposure during puberty than after irradiation in adult life. To protect young patients with scoliosis, who commonly receive multiple x-ray exposures during their adolescent years, a number of techniques have been devised to decrease radiation doses to breast tissue. These include using a posteroanterior projection, breast shields, fast rare earth screen-film combinations, increased filtration in the x-ray tube collimator, and lower grid ratios and higher kilovoltages.
Pregnancy Screening
All female patients age 10 years and older should complete a pregnancy information form that elicits the following: (1) menarchal status; (2) date of last menses; and (3) sexual activity. The form can be read to the patient by the technologist to ensure the patient’s comprehension. If the possibility of pregnancy exists, radiographic procedures are not performed until the patient consults her ordering physician. The radiographic procedure is performed if the patient subsequently has a negative pregnancy test or if the ordering physician deems the x-ray examination necessary. In the latter event, all measures are taken to deliver the lowest ionizing radiation dose to the patient and fetus.
Computed Tomography
In the early 1970s, Hounsfield introduced the first CT scanner to the medical community. Since that time the availability and use of this imaging modality have exploded. Also, there have been remarkable technologic advances in imaging and postprocessing equipment, providing higher resolution studies with greater detail, less noise, and faster acquisition times. This has been a particular advantage in the pediatric patient who is more likely to have difficulty remaining motionless for a lengthy diagnostic examination. Significant advances in automated multiplanar and three-dimensional postprocessing have also contributed to the usefulness of CT, particularly in the assessment of complex bony anatomy and pathology in musculoskeletal disorders.
It has been estimated that at least 65 million CT examinations are performed in the United States each year and that 7 million of these are in the pediatric patient. Similar to radiography, CT uses ionizing radiation to create images and therefore carries the associated risk of potential biologic effects from this exposure. The linear nonthreshold model of radiation risk states that there is no “safe” dose below which a patient is guaranteed no increased risk of malignancy. These risks are greater in the pediatric patient because their tissues are more radiosensitive, the doses they receive are cumulative, and they have a longer lifespan to develop a malignancy. Previous published reports on radiation risks were based on extrapolation from atomic bomb survivors. More recently the American Academy of Physicists in Medicine (AAPM) position is that “the risks of medical imaging at effective doses below 50 mSv for single procedures or 100 mSv for multiple procedures over short time periods are too low to be detectable and may be nonexistent.” However, the benefits of the use of this important diagnostic tool must still be weighed against the risks on a case by case basis.
The responsibility to reduce a patient’s radiation exposure falls on the ordering clinician and the radiologist, radiology technologist, and imaging department. It is important that the ordering clinician and radiologist consider alternative imaging modalities that do not use ionizing radiation, such as MRI or sonography, when appropriate. If CT is the modality of choice to diagnose a specific problem accurately it should be used, but with attention to limiting the scan to cover only the region of interest and in most cases with only one acquisition through the anatomy. Multiphase scans such as preiodinated and postiodinated contrast scans should be avoided unless absolutely necessary because this doubles the dose that the child receives. Pediatric CT protocols that are tailored to the patient’s size should always be used. Also, image techniques can be reduced even further for high-contrast examinations such as bone CT. Tube current modulation and in-plane shielding of radiosensitive tissue such as the orbits and breasts will also further reduce dose to the patient. The reader is referred to the Image Gently website ( http://www.pedrad.org/associations/5364/ig ), created and updated by the Alliance for Radiation Safety in Pediatric Imaging for resources and protocols to assist in practice.
Clinical Applications
There are many applications in musculoskeletal imaging in which CT is useful, and it should be used when it is the most appropriate imaging modality to answer a clinical question. Potential indications include preoperative assessment of complex congenital bony spine anomalies, spondylolysis and spondylolisthesis, torticollis or other rotational spinal deformities, tarsal coalition, osteoid osteoma, bony involvement in chronic osteomyelitis (e.g., sinus tract, sequestrum), intraarticular loose bodies, and evaluation of malpositioned hardware. Figures 10-13 through 10-24 and Box 10-1 outline many of the pediatric musculoskeletal disorders that are readily evaluated by CT. Also, throughout the text, relevant examples of the use of CT are provided.
