Principles of Assessment and Evaluation

Principles of Assessment and Evaluation (46)

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Imaging Techniques Relative to Rehabilitation

Imaging Techniques Relative to Rehabilitation (39)

 A brief presentation of imaging techniques of interest to the physiatrist must necessarily be selective. Because the diagnosis and initial treatment of fractures are primarily the responsibility of the orthopedic surgeon, with the rehabilitation professional typically involved only later in the course, a full discussion of fractures is not presented in this chapter. Only those fractures that bring patients under the long-term care of the physiatrist are included (e.g., vertebral fractures with the potential to damage the spinal cord). Similarly, tumors and infectious processes are de-emphasized. Rather, emphasis is placed on imaging degenerative musculoskeletal processes, spine and head trauma, stroke, and degenerative central nervous system (CNS) diseases commonly seen by the physiatrist. We will also cover imaging in sport medicine as this is a rapidly changing area in radiology and review the current applications of diagnostic ultrasound in the evaluation of musculoskeletal disorders.

In the past two decades, computed tomography (CT) and magnetic resonance imaging (MRI) have become the most sophisticated imaging modalities for evaluating the musculoskeletal system and the CNS. Therefore, this chapter focuses mainly on the recent applications of CT and MRI in the imaging of musculoskeletal and neural pathology of interest to the physiatrist. In the final section, we will introduce some relatively new imaging technologies of interest to the physiatrist, including advanced MRI methods and ultrasound imaging (USI).

The role of plain film examinations in the assessment of abnormalities of specific joint disorders is well established in the medical literature. A brief review of the most commonly performed radiographic examinations of the extremities will be done when addressing the specific subject. 

 

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The Physical Examination

The Physical Examination (4)

The hallmark of medicine has always been the physical examination. Perhaps more than the actual diagnosis, the process by which the physician arrives at his or her conclusion has defined the "art" of medicine. Much has been written about the techniques by which this art is performed, and much more will continue to be written. Each generation will take from the past and apply these techniques to the future of medicine.

The physical examination is an extension of the history and extends the doctor-patient relationship initially established during the history. The skill with which the examination is performed instills a sense of confidence in the patient that the examiner knows what he or she is doing. This confidence in the physician has a positive outcome on the patient's ability to recover. Finally, the physical examination serves to narrow the list of diagnostic possibilities.

In a specialty like physiatry, in which the whole person is evaluated in terms of function, there is no adjunct more important than the physical examination. The examination provides the foundation to formulate a plan to improve a person's function. Importantly, though, in looking at function, each piece must be applied to the whole person. The examination of one joint must be applied to the whole picture of the patient, and an understanding of functional biomechanics will enable the physician to include in the physical examination other structures that may indirectly contribute to the impairment.

The focus on function and application to the whole person in physiatry can be best seen in understanding the concept of the kinetic chain. No one joint, bone, or muscle acts alone in the body. An ankle sprain can lead to low-back pain. Lowback pain can affect the serve of a tennis professional. Lateral epicondylitis can alter shoulder mechanics and lead to rotator cuff impingement. It is because of these relationships that the physiatrist must perform a thorough examination. It is this comprehensive manner that sets apart the physiatric approach from others. A thorough knowledge of the neuromuscular system and an understanding of functional biomechanics will narrow the focus of the examination so it can be done in a time-efficient manner. The relationship between the different joints and regions must be understood. In addition, a complete understanding of the muscles and their innervation is required.

An understanding of the muscle kinesiology and biomechanics is very important in the physical examination. Each muscle functions across one or more joints to provide motion or stabilization. One example would be the hamstrings. When the foot is planted, the hamstrings act in their primary function as powerful hip extensors. However, with the foot off the ground, they can become knee flexors. With a patient prone and the knee bent at 90 degrees, the gluteus maximus acts as the primary extensor because of the shortened hamstrings. Place the knee in full extension, and the hamstrings will once again act as hip extensors. We will look further into these types of relationships in the physical examination.

In today's medicine, there exists a tremendous amount of information to digest. The number of articles indexed in MEDLINE has grown in size from 1,098,000 citations in 1970 to 11,761,000 in 2000. The modern physician must have an understanding of the body down to a microcellular level. In addition, access to modern tests like magnetic resonance imaging (MRI) is achieved by a greater number of patients. Any test has its limitations, and in the example of the MRI, these can be multiple false-positive findings (1). The MRI should be used to confirm not make a diagnosis. Many physician referrals are generated from a radiologist's interpretation of a study, often without physical examination findings consistent with the results of the study. It is at this point that the well-trained physiatrist can be the link using evidence-based medicine as it applies to diagnosis, history, and physical examination.

Whole texts are dedicated to the physical exam. Due to the limits of one chapter, this will be an introduction to the physical examination and kinesiology of the cervical spine, shoulder, lumbar spine, and knee. That said, the reader should be able to approach any joint in the manner laid out here to aid in his or her diagnosis. Examination of any joint should be performed in a systematic approach. As the examination begins, the clinician should make sure that the area to be examined is properly exposed for evaluation and the patient appropriately draped. We have focused on the major joints seen in our practice—the cervical and lumbar regions of the spine, the shoulder, and the knee. Other joints will be addressed in chapters in this text. We will now address the physical examination, and the kinesiology of the muscles and joints will be explained. For reference, the dermatomes, myotomes, and sclerotomes are illustrated in Chapter 21.

It is the task of the physiatrist to perform a thorough physical examination to confirm his or her diagnosis derived from the history and additional information. It even is more important today, because of the additional tests modern technology has advanced, to understand physical examination maneuvers and their diagnostic relevance.

Joseph H. Feinberg and Peter J. Moley

Source: Physical Medicine and Rehabilitation - Principles and Practice
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For the assessment of shoulder instability and labral tears, it is imperative that intra-articular contrast medium be injected in order to be able to evaluate the entire articular labrum, glenoid fossa, and capsular mechanism (12). Axial MR images provide the best visualization of the anterior and posterior glenoid labra, capsule, and lower rotator cuff muscles (Fig. 6-1). Anteriorly, the moderate–signal-intensity subscapularis muscle belly and its low–signal-intensity tendon are visualized. The tendon fuses with the low–signal-intensity anterior capsule as it courses to its insertion on the lesser tubercle. The fibrocartilaginous anterior and posterior labra appear as low–signal-intensity triangular or rounded areas attached to the glenoid rim. The higher–signalintensity intra-articular contrast opposed the hyaline cartilage surfaces of the glenoid and humeral head. The posterior capsule is visualized as a low-intensity area blending with the deep surface of infraspinatus and teres minor muscles as they extend to their insertions on the greater tubercle of the humerus. The long tendon of the biceps is demonstrated as a round, low– signal-intensity area within the bicipital groove.

Shoulder instability and the associated disruption of the anterior capsular mechanism can cause chronic shoulder pain and disability. The instability may be caused by an acute traumatic

episode or can occur with no history of a traumatic event. Both recurrent traumatic subluxation and nontraumatic instability are typically associated with disruption of the anterior capsular mechanism. Anteriorly, where most instability occurs, this mechanism includes the subscapularis muscle and tendon, the anterior joint capsule, three underlying glenohumeral ligaments, the synovial lining, and the anterior labrum. With instability, the labrum shows tears, separation from the glenoid rim, or degeneration (13). Also frequently present are medial stripping of the capsule from its normal attachment to the labrum and glenoid rim, an enlarged fluid-filled subscapular bursa secondary to joint effusion, attenuation of the glenohumeral ligaments, and injury or laxity of the subscapularis muscle or tendon.

By MRI, labral tears may be visualized as discrete linear areas of increased signal intensity within the normal signal void of the labrum (Figs. 6-6 and 6-7). These areas show moderate intensity on T1-weighted images and high intensity on T2-weighted images. With recurrent dislocation or subluxation, the labrum can become fragmented or attenuated.

FIGURE 6-6. SLAP lesion and posterior labral tear in a patient with history of posterior instability. A: Coronal oblique T1-weighted fat suppressed MR arthrogram demonstrates increased signal intensity within the BLC extending on the biceps tendon (arrowhead) characteristic of a type IV SLAP lesion. B: Axial T1-weighted MR arthrogram demonstrates increased signal within the posterior labrum (arrowhead ). There is a cyst within the posterior aspect of the spinoglenoid notch with high–signal-intensity contrast extending into the cyst.

FIGURE 6-7. Bankart lesion. A: Axial T1-weighted images of a left shoulder MR arthrogram demonstrate the fibrocartilaginous Bankart lesion of the anterior glenoid labrum (arrow). B: Coronal T1-weighted fat suppression demonstrates the inferior (short arrow) and the superior (long arrow) extensions of the labral tears.

Capsular detachment from the scapula (i.e., stripping) is visualized by T2-weighted MRI as an area of high–signalintensity fluid dissecting medially from the glenoid rim. With trauma to the subscapularis tendon, there can be medial retraction of the muscle-tendon junction when the tendon is completely ruptured. Chronic atrophy of the subscapularis muscle belly is identified by high–signal-intensity fatty replacement. The glenoid marrow underlying a labral detachment may show pathologically decreased signal intensity even before the plain film radiograph shows an osseous Bankart lesion. MRI and CT can be used to visualize Bankart fractures of the anterior glenoid and the Hill-Sachs compression deformity of the posterolateral humeral head (14,15) and are both useful in the assessment of the extent of a Hill-Sachs defect in patients with engaging lesions. Patients with the rarer posterior instability show similar posterior labral, capsular, and muscular defects.

Refferences

Source: Physical Medicine and Rehabilitation - Principles and Practice

The MRI findings of shoulder impingement syndrome and its associated supraspinatus injury are best seen on oblique coronal MR images that visualize the full length of the supraspinatus muscle belly and tendon (Fig. 6-1B). The normal muscle belly displays moderately low signal intensity. The tendon is visualized as an intermediate–signalintensity structure that blends with the low signal intensity of the superior capsule as it courses to its insertion on the greater tubercle of the humerus. The tendon demonstrates smooth tapering from medial to lateral into its insertion in the greater tuberosity. The inferior aspect of the tendon is delimited below by the moderate signal intensity of the hyaline cartilage on the superior aspect of the humeral head. The superior aspects of both the muscle belly and tendon are delimited by a high–signal-intensity subacromial and subdeltoid fat plane. The normal subacromial-subdeltoid bursa is not specifically visualized because its walls are separated only by monomolecular layers of a synovial-type fluid, but it is situated between the supraspinatus tendon and the fat plane. Above the fat plane, the clavicle, acromioclavicular joint, acromion, and deltoid muscle are demonstrated on different oblique coronal sections.

Although rotator cuff impingement is a clinical diagnosis, MRI can provide direct visualization of the constituents to the coracoacromial arch and their relationship to the supraspinatus (Fig. 6-2A and B). Downward slanting of the acromion in the coronal or the sagittal plane, a thickened coracoacromial ligament or inferior osteophytosis within the acromioclavicular joint can exert mass effect upon the supraspinatus. This has been implied as being in part responsible for chronic tears of the supraspinatus.

 

FIGURE 6-2. A: Coronal oblique T2-weighted pulse sequence with fat suppression demonstrates downward slanting to the acromion (long arrow ), which is against the supraspinatus tendon (*). Note focal area of increased signal at the myotendinous junction of the SsT (short arrow ). B: Sagittal oblique T2WI with fat suppression demonstrates to a better advantage the inferior slanting to the acromion against the SsT (short arrow ). Note focal tendinosis (long arrow ).

 

FIGURE 6-3. A: T1-weighted MRI of focal supraspinatus tendinosis demonstrating focal thickening and slight increase signal intensity to the tendon (arrow ). B: CoronalobliqueT2-weightedfat suppressed sequence with increased signal intensity within the area of tendinosis (arrowhead ). There is fluid within the adjacent subdeltoid bursa (long arrow ). C: Sagittal oblique T2-weighted fat suppressed image demonstrates the area of increased signal to be within the anterior superior portion of the rotator cuff representing fibers of the supraspinatus tendon (short arrow ).

Neer stated that 95% of rotator cuff tears are associated with chronic impingement syndrome (7) and described three stages in the progression of rotator cuff injury. These can be visualized by MRI (6–10). Stage 1 is characterized by edema and hemorrhage within the supraspinatus tendon characteristic of an early tendinitis. On MRI, there is focal tendon thickening and diffuse moderate increase in signal intensity within the tendon (Fig. 6-3A–C). In stage 2, Neer described both inflammation and fibrosis within the tendon. MRI shows this as thinning and irregularity of the tendon. Stage 3 is a frank tear of the supraspinatus tendon. On MRI, complete tears are noted by a discontinuity of the tendon with a well-defined focus of high signal intensity on T2-weighted images (Fig. 6-4). The most susceptible area is the critical zone of hypovascularity, located about 1 cm from the insertion (11). With small or partial tears, there is no retraction of the muscle-tendon junction, the subacromial-subdeltoid fat plane is commonly obliterated, and fluid may accumulate in the subacromial-subdeltoid bursa, which becomes hyper- intense on T2-weighted images. There also may be effusion of the shoulder joint, which may extend inferiorly along the tendon sheath about the long head of the biceps. With a complete supraspinatus tendon tear, the muscle belly may retract medially, and atrophy may occur as the tear becomes chronic (Fig. 6-5A,B). Muscle atrophy appears as areas of high signal intensity because of fatty replacement within the muscle belly and decreased muscle mass. Finally, the acromiohumeral interval narrows as the humeral head migrates superiorly, because of the loss of supraspinatus restraint to the deltoid’s tendency to sublux the humerus superiorly during abduction.

FIGURE 6-4. Complete rupture of the supraspinatus tendon is seen in a T2-weighted MRI. There is fluid filling the gap (arrow) and there is retraction to the tendon fibers underneath the acromion.

FIGURE 6-5. Complete rotator cuff tear. A: Coronal oblique T1-weighted image. There is intermediate signal intensity (*) from the inflammatory reaction replacing the normal low signal to the SS tendon. B: The edge (arrow) to the retracted tendon is at the level of the superior labrum. There is increased signal intensity filling the gap of the retracted tendon (long arrow).

Refferences

Source: Physical Medicine and Rehabilitation - Principles and Practice

Plain film radiographic evaluation of the shoulder should include frontal examinations with internal and external humeral rotation. If there is a question of instability or dislocation, an axillary view, a scapular Y view, or both should be obtained. There have been several reports that recommend the use of a 30-degree caudad-angled radiograph or a suprascapular outlet view for the assessment of the anterior acromion in cases of suspected shoulder impingement. Since these are special views, they must be ordered as routine shoulder radiographs do not include axillary or suprascapular outlet views. The RRL for plain film radiographic examinations of the shoulder is less than 0.1 mSv, which is considered minimal.

MRI has become valuable in evaluating a host of shoulder abnormalities very familiar to the physiatrist. These include impingement syndrome, other rotator cuff abnormalities, instability syndrome, and bicipital tendon abnormalities. It is also useful in demonstrating arthritic changes, occult fractures, ischemic necrosis, and intra-articular bodies. MRI with intra- articular contrast is now considered the modality of choice for the evaluation of labral and capsular pathology. The use of MRI for shoulder evaluation avoids radiation exposure to the nearby thyroid gland, which can occur with CT examinations.The excellent visualization of marrow by MRI permits early diagnosis of ischemic necrosis, infection, and primary or metastatic tumors.

Because of the oblique orientation of the scapula on the chest wall and the consequent anterolateral facing direction of the glenoid, the direct multiplanar imaging capability of MRI provides optimal visualization of all the important shoulder structures. An oblique coronal image parallel to the plane of the scapula provide full-length views of the rotator cuff musculature, especially the supraspinatus and is the best plane for the evaluation of injuries to the biceps-labral complex (BLC) (Fig. 6-1A and B). Coronal oblique images can also provide information about the presence of impingement upon the supraspinatus by the acromion and osteophytes in the presence of acromioclavicular joint osteoarthritis. Oblique sagittal imaging planes parallel to the glenoid provide cross-sectional views of the rotator cuff apparatus and evaluates the anatomical configuration of the coracoacromial arch and the presence of impingement (Fig. 6-1D). Axial imaging planes provide good visualization of the anterior and posterior capsular apparatus, glenoid labrum, bony glenoid rim, and humeral head (Fig. 6-1C).

FIGURE 6-1. Normal shoulder MR images. A: An axial scout film with cursors displays the oblique coronal planes parallel to the plane of the scapula, which allow optimal visualization of the supraspinatus. B: An oblique coronal image demonstrates the supraspinatus muscle belly (SsB), supraspinatus tendon (SsT), subacromial-subdeltoid fat plane (FP), acromioclavicular joint (ACJ), deltoid muscle (D), articular cartilage of humeral head and glenoid (AC), glenoid (G), and humeral head (H). C: An axial image displays humeral head (H), glenoid (G), glenoid labrum (L), the inferior glenohumeral ligament (IGL), deltoid muscle (D), subscapsularis tendon (ScT), and biceps tendon (BT). D: A sagittal section demonstrates good resolution of the coracoacromial ligament (CAL) extending from the coracoid process (CP) to the acromion; coracoid process (CP), supraspinatus (SS), infraspinatus (IS).

Refferences

Source: Physical Medicine and Rehabilitation - Principles and Practice

The advent of the multidetector CT (MDCT) scanner has increased the applicability of this imaging technique for the assessment of the musculoskeletal system. This technology allows for the acquisition of large data set in the axial plane that can be reconstructed in multiple planes of imaging with the use of multiplanar reconstruction (MPR) algorithm.

Any anatomical part in the human body can now be scanned in the axial plane and the anatomical information can later be reconstructed in the sagittal, coronal, or any orthogonal plane desired in order to better assess complex anatomical structures such as the joints of the axial skeleton and the spine (1).

CT provides poor contrast resolution to evaluate the musculoskeletal system. Since the relative soft-tissue density of cartilage, tendons, and muscle is similar, we cannot resolve adequate soft-tissue differences between these structures. For example the articular cartilage can only be assessed with CT after a positive contrast is introduced in the joint space such as is the case with CT arthrography. CT however provides a superb spatial resolution that allows for the accurate evaluation of fine soft-tissue and bone trabecular details.

CT images may be displayed with various windows suitable to resolve different structures. Bone window images provide the highest resolution of compact and cancellous bone. Soft- tissue window offers moderate resolution of muscle, tendon, ligament, fat, cartilage, and neural structures.

The good resolution and enhanced contrast of MRI for soft-tissue structures, together with its direct multiplanar imaging capability, make it a superb modality for evaluating all the principal constituents of the musculoskeletal system. Although a technical discussion of the physics of MRI is beyond the scope of this chapter, the physiatrist should know the normal and abnormal MRI appearance of various tissues to be able to look at an MR image with confidence and explain the findings to a patient. The MRI signal intensity of any tissue primarily reflects its proton density, its T1 relaxation time, and its T2 relaxation time. Various techniques, including manipulating the repetition time (TR) between the application of radiofrequency pulses or the echo time (TE) between the radiofrequency pulse and the recording of a signal (i.e., echo) produced by the tissue, can emphasize the proton density, T1 relaxation time, or T2 relaxation time features of any tissue (2). The TR and TE are expressed in milliseconds. The most commonly used technique is spin echo, in which short TR and TE will emphasize the T1 relaxation time of a tissue, the so- called T1-weighted image. In general, an image is said to be T1 weighted if TR is less than 1,000 ms and TE is less than 30 ms (e.g., TR = 500 ms, TE = 20 ms). A T2-weighted image generally is accomplished with a TR longer than 1,500 ms and a TE greater than 60 ms (e.g., TR = 2,000 ms, TE = 85 ms). Proton density images are obtained with a long TR and a short TE (e.g., TR = 2,000 ms, TE = 20 ms).

FIGURE 6-1. Normal shoulder MR images. A: An axial scout film with cursors displays the oblique coronal planes parallel to the plane of the scapula, which allow optimal visualization of the supraspinatus. B: An oblique coronal image demonstrates the supraspinatus muscle belly (SsB), supraspinatus tendon (SsT), subacromial-subdeltoid fat plane (FP), acromioclavicular joint (ACJ), deltoid muscle (D), articular cartilage of humeral head and glenoid (AC), glenoid (G), and humeral head (H). C: An axial image displays humeral head (H), glenoid (G), glenoid labrum (L), the inferior glenohumeral ligament (IGL), deltoid muscle (D), subscapsularis tendon (ScT), and biceps tendon (BT). D: A sagittal section demonstrates good resolution of the coracoacromial ligament (CAL) extending from the coracoid process (CP) to the acromion; coracoid process (CP), supraspinatus (SS), infraspinatus (IS).

Most normal tissues demonstrate similar signal intensities on both T1- and T2-weighted images. Compact bone, fibrocartilage, ligament, tendon, and the rapidly flowing blood within the blood vessel typically produce very low signal intensity, referred to as a signal void, and appear black both on T1 and T2 (Fig. 6-1). Muscle demonstrates moderately low signal intensity and appears dark gray. Peripheral nerves demonstrate slightly higher signal intensity than muscle because of the fat content of their myelinated fibers. Hyaline cartilage produces

moderate signal intensity and appears light gray. Fat produces very high signal intensity and appears bright on T1 and T2. Because fat is frequently situated adjacent to ligaments and tendons, it can provide a high-contrast interface for evaluating the integrity of these structures. Adult bone marrow also shows high signal intensity because of its high fat content. Most normal body fluids that are not flowing show low signal intensity on T1-weighted images and high signal intensity on T2-weighted images.

Pathologic processes such as tumor, infection, and abnormal fluids (e.g., edema, joint effusion) show intermediate signal intensity on T1-weighted images and become very hyperintense on T2-weighted images. Pathologic calcifications demonstrate very low signal intensity on both T1-and T2-weighted images.

The direct multiplanar imaging capability of MRI is particularly useful in evaluating obliquely oriented musculoskeletal structures such as the supraspinatus tendon, the cruciate ligaments, and the lateral collateral ligaments of the ankle.

MRI has proved useful in evaluating traumatic, degenerative, inflammatory, and neoplastic pathology of the limbs and spine. It is useful in detecting acute or chronic traumatic injuries and degenerative conditions involving bones, muscles, tendons, ligaments, fibrocartilage, and nerves. Bone pathology, particularly well detected by MRI, includes contusions, osteochondral injuries, stress fractures, marrow replacement by neoplastic cells, and ischemic necrosis. Muscle lesions that MRI is especially sensitive at identifying include strain or contusion, complete rupture, compartment syndrome, myopathies, and atrophy (3). Tendon conditions well depicted by MRI include partial and complete tear, tendinitis, and tenosynovitis. MRI is also very sensitive for detecting partial or complete ligament tears. Fibrocartilaginous injuries or diseases well delineated by MRI include pathology of the menisci, the glenoid labrum, the triangular fibrocartilage of the wrist, and the intervertebral disc. Nerve entrapments well visualized by MRI include spinal nerve encroachment by disc disease or spinal stenosis and carpal tunnel syndrome (CTS) or other entrapment syndromes. Enhanced imaging of normal and injured peripheral nerves can be obtained using a short-tau inversion recovery (STIR) excitation-emission sequence due to the increased sensitivity to free water content associated with tissue edema using this MR recording protocol. The increased signal generated by injured nerves using STIR pulse sequences probably reflects an increase in free water content of the nerve due to altered axoplasmic flow, axonal and/or myelin degeneration, and endoneurial or perineurial edema due to a breakdown in the blood-nerve barrier (4). MRI imaging of denervated skeletal muscle shows increased MR signal using the STIR protocol when there is significant muscular weakness and well-defined changes indicating muscle denervation on needle electromyography (5).

Osteomyelitis causes a reduction in bone marrow signal intensity on T1-weighted images because of the replacement of normal fatty marrow by inflammatory exudate. In T2-weighted images, these areas of active infection become hyperintense.

MRI has particular value in evaluating both bone and soft-tissue neoplasms. Most of them demonstrate moderately low signal intensity on T1-weighted images and very high signal intensity on T2-weighted images.

Emphasis will now be directed to the application of imaging modalities to common regional pathologic conditions of the musculoskeletal system. Particular focus will be given to MRI because of its superb soft-tissue imaging capabilities and its rapidly expanding diagnostic applications.

The important role played by radiology in the diagnosis of diseases has come at the expense of increased radiation exposure to the general population. With the advent of new technology, such as Positron Emission Tomography (PET) studies and MDCT technology, there has been a sharp increase in the number of radiographic examinations performed to the general population and as a consequence an increase in the cumulative radiation dose to the individual patient and the general population. It is an expected outcome for increase in radiation exposure to lead to an increased rate of malignancy. Therefore, increased awareness is needed in issues concerning radiation safety.

Ionizing radiation, especially at high doses, is known to increase the risk of developing cancer. It is estimated that medical exposure might be responsible for 1% of cancer diagnosis in the United States. This rate is expected to increase in the coming years due to the increased number of examinations performed today.

The scientific measurement for the effective dose of radiation is the millisievert (mSv). The background radiation dose for the average person in the United States is about 3 mSv. This is secondary to cosmic radiation and naturally occurring radioactive materials. By comparison, the effective radiation dose for a spinal CT is equivalent to 6 mSv or 2 years of natural background radiation. Radiation exposure is particularly important in pregnant women and pediatric patients due to the cumulative life effect of radiation exposure at a younger age. In nuclear medicine examinations, special precautions are needed. Some of the radiopharmaceuticals used in nuclear medicine can pass into the milk of lactating women (6).

The relative radiation level (RRL) is a radiation measurements used to calculate effective dose. This is the dose used to estimate population total radiation risk associated to an imaging procedure. This takes into account the sensitivity of different body organs and tissues. This estimate cannot assess the specific risk of an individual patient.

Every effort should be made to order examination, which is best indicated to address the clinical concern of the patient. To aid in this regard, the American College of Radiology (acr. org) has established guidelines for the appropriate use of imaging to answer specific clinical questions. The appropriateness criteria can be of help when deciding which imaging study to order to answer a clinical question.

Refferences

Source: Physical Medicine and Rehabilitation - Principles and Practice
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