Diagnostic Imaging for Physical Therapists PDF

Introduction to Musculoskeletal Imaging Most musculoskeletal injuries occur as a result of either trauma or overuse. Following a thorough evaluation by a qualified health-care professional, most patients are usually required to have a basic radiographic (x-ray) examination of the in...

Introduction to Musculoskeletal Imaging Most musculoskeletal injuries occur as a result of either trauma or overuse. Following a thorough evaluation by a qualified health-care professional, most patients are usually required to have a basic radiographic (x-ray) examination of the injured area to assist in confirming the diagnosis. Many of these individuals, however, will require the use of an advanced imaging modality such as ultrasound, computed tomography (CT), and/or magnetic resonance imaging (MRI) to increase the accuracy in diagnosing the specific nature of the injury. Radiographic Views When performing a typical radiographic procedure, the radiologic technologist will position the patient and the anatomic part to be radiographed for two or more radiographic views. These views usually consist of: ▪ An anteroposterior (AP) or posteroanterior (PA). Page 2 of 230  ▪ An oblique (usually a 45-degree rotation from the AP or PA position). ▪ A lateral (90-degree rotation from AP or PA position). Rotating the anatomy into these angled positions allows the clinician to better define the location of structural change. For some anatomic structures such as wrists, shoulders, and knees, the patient may need to have additional views performed. Additional radiographic views may be required on a patient-by-patient basis. For example, the ulnar flexion may be used to demonstrate a fracture of the navicular bone. Advantages and Disadvantages Diagnostic radiography is the most economic imaging modality. Diagnostic information like fractures, bony lesions (osteoblastic and osteolytic), dislocations, subluxations, and edema may be visible. When soft tissue is imaged for calcification deposits and foreign bodies, it is suggested that the radiographic technique factor kilovoltage (kV) be reduced 10 kV lower than the standard radiographic technique. Page 3 of 230  This results in an increase in the subject contrast between soft tissue and bone. Since diagnostic x-rays produce ionizing radiation, every attempt should be made to protect the patient from the unnecessary exposure that may occur as a result of insufficient patient or examination information, repeat examinations, or performing the wrong examination. To make this process as effective as possible, a qualified physician must complete a request for all radiographic procedures. Pertinent patient information and type of x-ray procedure requested should be provided on the x-ray request form in an accurate and legible manner. Any additional information or concern that may benefit the quality or safety of the x-ray procedure should be communicated (e.g., patient history, patients that may require sedation, pregnancy) to either the radiologic technologist or the radiologist. Ultrasound The applications of ultrasound to the medical field subsequently followed the development of sonar (sound navigation ranging) and its use during World War II. Since its earlier uses in medical imaging, medical diagnostic sonography, sometimes referred to as sonography or ultrasound, has experienced substantial growth in its applications in imaging the human body. From its initial uses in obstetrics and gynecology to imaging small abdominal structures and assisting with biopsy procedures to its current use in vascular, echocardiographic, and now musculoskeletal imaging, ultrasound continues to make significant contributions to medical imaging. Page 4 of 230  The concept of using conventional ultrasound to evaluate the musculoskeletal system is not a new idea. It dates back to the late 1970s. The advancements made in ultrasound with the development of high frequency transducers in the range of 5 to 12 MHz has demonstrated the ability to visualize musculoskeletal structures such as tendons, ligaments, articular cartilage, fibrocartilage, peripheral nerves, muscles, and bone. Higher frequency transducers produce a better signal-to-noise ratio; however, high-frequency transducers are limited to the depth of tissue they can penetrate. Lower frequency transducers, therefore, are used to image deeper structures such as the hip and posterior knee. A new method of imaging called “tissue harmonic imaging,” which is different from conventional ultrasound, allows deeper penetration with better image quality compared to conventional ultrasound. A B Rotator cuff tear (arrow) demonstrated. A. Conventional ultrasound. B. Harmonic imaging. Page 5 of 230  Conventional ultrasound is accomplished by sending a sound wave from the transducer into a structure and receiving an echo reflected off structures in the body and back to the transducer. In harmonic imaging, instead of listening for the same echo that was sent in the conventional manner, harmonic imaging listens for an echo at twice the transmitted frequency. The spatial resolution in harmonic imaging is also improved, which permits better visibility of smaller structures. Advantages and Disadvantages Ultrasound obtains its image without utilizing harmful ionizing radiation. It is portable, which improves accessibility to the patient and allows for dynamic evaluation of joints. In addition, an ultrasound examination is relatively low in cost compared to other imaging modalities such as CT and MRI. The use of ultrasound to assist with guided interventional procedures such as aspirations, biopsies, and medication delivery also provides pinpoint accuracy and timely means of diagnosing and treating patients. Operator dependence is probably its best-known limitation. Computed Tomography Computed Tomography (transmission tomography) has experienced several modifications in its basic design since its initial development in the early 1970s. The most recent technologic advancement, however, was the development of spiral CT. Page 6 of 230  Through the development of slip-ring technology used in a spiral CT scanner, the x-ray tube can continuously rotate around the patient as the patient moves through the opening of the CT scanner, whereas conventional CT scanners performed an examination in a slice-by- slice (axial) method. Left (A) Conventional (Cine) CT scan. Right (B) Spiral (Helical) CT scan. The continuous movement offered through spiral CT greatly reduces scan time, provides volumetric scanning, and multislice capability. The number of slices (images) a CT scanner can acquire per revolution of the x-ray tube depends on the number of rows of detectors. Spiral CT units today may be referred to as multislice (MSCT) or multidetector CT scanners. Over the past few years, the medical profession has experienced a doubling effect in multislice technology. With the current number of slices acquired per revolution in most scanners being 32 slices, some manufactures have already developed and are marketing 64- slice scanners. Page 7 of 230  The future of multislice technology is focused on 128 slices per revolution with a possibility of developing 256-slice units using a different x-ray beam design. These multislice scanners can produce slices that are submillimeter in thickness and can acquire these images in less than a second. Decreasing the slice thickness produces an increase in the spatial resolution and the ability to visualize smaller structures accurately. Advantages and Disadvantages With the development of slip-ring technology, the x- ray tube travels around the patient without having to stop and reset itself between slices as was the case with the more conventional CT units. Slip-ring technology allows continuous data acquisition with reduced scan time. In some cases, the CT examination can be performed in a single breath-hold, which helps to eliminate respiratory motion. In performing a chest examination, the chance of missing a lesion along the border of the diaphragm, such as in the lung base or liver, is reduced. Page 8 of 230  Since CT images are in a digital (soft-copy) format, they can be windowed to focus on the soft tissue, lung tissue, or bony tissue by adjusting the density and contrast scale of the image data. Other benefits offered through the use of MSCT are the high-quality images (improved contrast resolution) produced through various software-generated reconstruction methods. These reconstruction methods include: ▪ Volume rendering (VR). ▪ Shaded surface display (SSD). ▪ Multiplanar reformation (MPR). ▪ Maximum intensity projection (MIP). Multiplanar reformatted images are two-dimensional images that have been reconstructed through a computer software process using the previously acquired axial (transverse) images. A B C CT of the wrist demonstrating a fracture of the hamate. A. Axial image showing fracture (arrow). B. Coronal MPR image with sagittal slice overlay. C. Sagittal MPR image showing fracture (arrow). A B C Severely comminuted and angulated bimalleolar fracture of the ankle. A. Axial CT through lower leg. B. Sagittal MPR showing fracture (arrow). C. Coronal MPR demonstrating bimalleolar fracture (arrows). MPR images are commonly reformatted into coronal or sagittal images. Page 9 of 230  This reconstruction method is usually used in musculoskeletal and spine applications but may also be used in other areas including the brain, thorax, abdomen, and pelvis. Coronal multiplanar reformatting. The MIP reconstruction method can be used in vascular applications; however, it is commonly used in MR angiography (MRA). In this reconstruction method, only the voxels (volume element) with the brightest intensity (maximum intensity) are selected and reconstructed to form the Maximum intensity projection (MIP) of three-station image. MRA of the peripheral arteries. Images reconstructed with Shaded surface display demonstrating a the SSD method provide a complex tibial plateau realistic three-dimensional fracture involving both medial and lateral (3D) view of the surface of the aspects of the tibia. Note the SSD image is structure. Applications for rotated to show a posterior oblique view SSD include orthopedic and of the fracture. vascular structures. Volume rendering is a complex, yet versatile, three-dimensional reconstruction method that combines the characteristics of SSD and MIP. Page 10 of 230  Anatomic structures of interest are identified from the initial axial images by their respective CT number, and the VR reconstruction method is applied. Color coding of the tissues may be performed, thus allowing for visual differentiation of various tissues. A B Volume-rendering reconstruction method demonstrating (A) normal peroneus longus tendon (arrow) and (B) torn peroneus longus tendon (arrow). VR is quickly becoming the 3D method of choice due to the speed at which CT workstations are able to process data. Images that are reconstructed using MIP, SSD, or VR can be rotated and viewed from any angle to provide a better understanding of complex 3D structures. Probably the two most common disadvantages associated with CT is: ▪ The possible risk of an adverse reaction to an intravenous (IV) contrast agent if required. ▪ The increased concern regarding the use of CT (particularly in children) as the amount of radiation exposure is significant. Magnetic Resonance Imaging Introduction of MRI was in the early 1980s. Initially used for imaging the brain and spinal cord, MRI use has spread to include numerous applications covering the entire body. Page 11 of 230  MRI is often incorrectly considered a superior imaging modality to other imaging techniques. In many circumstances, it is inferior to CT, ultrasound, or even plain X-ray. Each set of images produced takes several minutes to obtain. Therefore, MRI is not suitable for patient who are unable or unwilling to remain motionless. MRI, the most technologically advanced imaging modality to date, can offer a wide range of imaging capabilities through the use of a strong external magnetic field, an arsenal of imaging radiofrequency (RF) coils, a variety of pulse sequences, and the availability of contrast media. MRI provides exquisite images of body parts that do not move, such as the brain, and anatomical structures that can be kept still, such as parts of the musculoskeletal system. The patient lies on the scanner couch (1) which slides into the bore of the scanner (2). Within the bore of the scanner there is a powerful magnetic field. The scanner produces radiofrequency pulses to ‘excite’ protons in the body. As the excited protons in the body ‘relax’ after each pulse, they give off radiofrequency ‘signal’ which is detected by the receiver (3). Page 12 of 230  MRI allows detailed analysis of musculoskeletal body parts such as the knee. Bone marrow is clearly visible – in the femur and tibia in this case. Bone cortex is less clearly visible on MRI and is often better seen with CT scans or plain X-rays. What are MRI images? X-ray and CT images can be considered to be a map of density of tissues in the body; white areas on X-ray and CT images represent high density structures. MRI images are different, in simple terms, MRI images can be considered as a map of proton energy within tissues of the body, in particular those that contain a large amount of fat or water. Bright areas on an MRI image represent Spine MRI shows abnormal high signal high ‘signal’ given off by protons in the density in the disc within the adjacent vertebral bodies at L3-L4 level body during the scanning process. (arrow). Bony destruction of vertebral bodies is seen in L3 and L4. White areas on an X-ray or CT image = high density. White areas on an MRI image = high signal. Page 13 of 230 MRI interpretation It’s all about FAT and WATER. The two basic types of MRI images are T1-weighted and T2- weighted images, often referred to as T1 and T2 images. On T1 images FAT is white. On T2 images both FAT and WATER are white. There are four basic pulse sequences that have been developed. They include: ▪ Spin echo (SE). ▪ Gradient echo (GE). ▪ Inversion recovery (IR). ▪ Echo planar imaging (EPI). Using a variety of parameters associated with MRI such as repetition time (TR), echo time (TE), inversion time (TI), and flip angle (FA), pulse sequences can be adjusted to produce images that provide information that is either: ▪ T1-weighted. ▪ Proton density weighted. ▪ T2-weighted. ▪ T2∗-weighted. ▪ IR. T1-weighted images are best used to demonstrate anatomic detail. A B T1-weighted images. A. Coronal image of the knee demonstrating joint effusion (arrow). B. Sagittal image of the index finger demonstrating osteomyelitis of the middle phalanx (low signal). Page 14 of 230  T2-weighted images are typically used to identify pathologic conditions. T2-weighted fast spin echo coronal of the knee with increased signal characteristic of a tear. Proton density–weighted images indicate the concentration of hydrogen protons and are beneficial in assessing articular cartilage. Proton density–weighted sagittal image of the knee demonstrating an anterior cruciate ligament tear. Note: Small joint effusion and small popliteal cyst. Images that are T2∗-weighted may exhibit an angiographic, a myelographic, or an arthrographic effect. T2∗-weighted (gradient echo) coronal image of the knee. Note: Small joint effusion and small popliteal cyst. Page 15 of 230 Sample T1& T2 images T1-weighted image – Anatomy (spine) T1 images can be thought of as a map of proton energy within fatty tissues of the body. Fatty tissues include subcutaneous fat (SC fat) and bone marrow of the vertebral bodies. Cerebrospinal fluid (CSF) contains no fat – so it appears black on T1-weighted images T2-weighted image – Anatomy (spine) T2 images are a map of proton energy within fatty AND water-based tissues of the body. Page 16 of 230  Fatty tissue is distinguished from water-based tissue by comparing with the T1 images – anything that is bright on the T2 images but dark on the T1 images is fluid-based tissue. For example, the CSF is white on this T2 image and dark on the T1 image above because it is free fluid and contains no fat. Note that the bone cortex is black – it gives off no signal on either T1 or T2 images because it contains no free protons. T1 weighted image – Pathology (spine) Loss of the normal high signal in the bone marrow indicates loss of normal fatty tissue and increased water content. Abnormal low signal on T1 images frequently indicates a pathological process such as trauma, infection, or cancer T2 weighted image – Pathology (spine) The same areas are whiter than usual on this T2 image indicating increased water content. Abnormal brightness on a T2 image indicates a disease process such as trauma, infection, or cancer. This patient had multiple myeloma. Page 17 of 230 Specialised MRI Sequences; STIR Image Specialised MRI images can be produced in order to answer specific clinical questions. Inversion recovery pulse sequences such as short-tau IR (STIR) and fluid attenuated IR (FLAIR) are used to null the signal coming from a specific tissue such as fat or cerebrospinal fluid (CSF), respectively. A B STIR pulse sequence demonstrating osteomyelitis (high signal) of the middle phalanx of the index finger. A. Sagittal (longitudinal) and B. axial views. A STIR pulse sequence, commonly used in musculoskeletal imaging, is used to null the signal from fat. This allows better visibility of free fluid and partial or complete tears. Contrast agents used in MRI are used with a T1-weighted pulse sequence. Historically, these contrast agents were used to assist with the diagnosis of pathologies related to the central nervous system. Page 18 of 230  When contrast agents are used in MRI to assess the joint space and surrounding structures, this procedure is commonly referred to as MR arthrography. Kinematic MR imaging (KMRI) is a technique that allows MRI technology to assess the function of the joint in order to detect and diagnose various musculoskeletal conditions. More specifically, KMRI allows the joint to be studied through a range of motion, while under stress, or under a loaded condition (weight-bearing). Some MRI units are specially designed and may be referred to as “dedicated” or “extremity” MR systems, and incorporate specific positioning devices and RF coils to facilitate the imaging of the joint. Other MR units incorporate devices to simulate weight-bearing conditions. In addition to performing kinematic imaging on the spine, joints such as the hip, knee, ankle, shoulder, wrist, and temporomandibular may also be imaged. The MRA scan (magnetic resonance angiography) is a form of an MRI and is performed with the same machine. The only difference is that the MRA takes more detailed images of the blood vessels than the organs or tissue surrounding them. Advantages and Disadvantages The biggest drawbacks would probably be the overall cost of the examination and some contraindications associated with the magnetic field. The benefits of MRI include excellent soft tissue contrast, increased visibility of tissue without bone artifact, and no ionizing radiation. Page 19 of 230  Since there is no ionizing radiation involved in the procedure, follow-up examinations and imaging of pediatric patients and pregnant patients can be performed safely. Generally, MRI is not advised in pregnancy, especially during the first trimester. Discussion with the radiology department will be required. Contrast agents are avoided in patients who are pregnant or breast feeding. MRI is preferred to computed tomography (CT) when doctors need more detail about soft tissues—for example, to image abnormalities in the brain, spinal cord, muscles, and liver. MRI is particularly useful for identifying tumors in these tissues. Since the magnetic field of most MRI units is on 24 hours a day, 7 days a week, strict safety guidelines must be followed. The safe utilization of MRI incorporates a screening of all patients and personnel prior to entering into the MR environment to rule out any contraindication that may pose a danger to the individual or health-care personnel. Limitations of MRI Subject to motion artifact. Inferior to CT in detection of bony injury. Inferior to CT in detecting acute hemorrhage. Requires prolonged acquisition time for many images. Contraindications to MRI Implanted devices and other metallic devices: ▪ Cochlear implants. ▪ Some artificial heart valves. ▪ Aneurysm clips and other magnetizable materials. ▪ Pacemakers and other implanted electronic devices. Page 20 of 230  Intraocular metallic foreign bodies. ▪ Screening CT of the orbits if history suggests possible metallic foreign body in the eye. Unstable patients (most resuscitation equipment cannot be brought into the scanning room). Pregnancy (relative contraindication due to unknown effects on the fetus). Other – severe agitation, or claustrophobia (may require anesthesia assistance). Thank You Click Here To Take The Quiz Page 21 of 230