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Although MR Imaging is the modality of choice for imaging the musculoskeletal system, CT remains a viable alternative.
Ability to evaluate a wide vairety of musculoskeletal problemss making CT an impotant diagnostic tool. With new alogrithrim for multiplanner (MPR) & (3D) three dimensional image reconstruction implemental. On faster, less costly work station, the continued importance of CT in musculoskeletal imaging has become solidified. Helical CT is shown to have significant advantages. Over dynamic CT by potentially eliminating interscan and interscan motion resulting in true volume data sets. The use of helical CT in the musculoskeletal system is benefit to patients in whom a CT is needed to defined the presence and extent of traumatic injury, inflammation & infection or other congenital or acquired anomaly.
General advatages of helical CT over conventional dynamic CT The advantages of helical CT over dynamic CT are :
Trauma patients may benefit most for helical CT due to rapid data acquisition as they have difficulty in remaining still or assuming certain radiography position. With helical CT, areas which are difficult to evaluate, including the shoulder joint & scapula, the bony pelvis & the spine can be examined rapidly.
Lesion detection and definition are enhanced with helical scan obtained at peak contrast enhancement. This provides excellent detail of the vascularity of the lesion. 3-D reconstruction using a volume - rendering shaded surface or maximum intaisity. Projection (MIP) programme can be helpful. MRI remains the primary modality for evaluation of muscle and soft tissue, but CT is playing an incrasing role, particulary in the very ill patient or in AIDs patient. In these cases scan obtained at the peak enhancement provides excellent detail of the vascularity and extent of the lesion. Another important role of helical CT in musculo-skeletal imaging is its ability to create 3-D vascular maps. CT angiography is valuable in humerous areas of the abdomen, including the renal arteries and hepatic vasculature, in chest (for pulmonary arteries) & the neck (for carotid arteries). MRI angiography does have specific advantages in selected cases helical CT angiography may be more economical & cost effective. helical CT is not prone to flow artifacts which are typical of MR angiography. Further work needs to be done with helical CT angiography to determine its value in musculoskeletal imaging.
CT has proved to be a critical examination particularly when there is discourdance between clinical findings, routine plain films and other radiological studies. In musculoskeletal imaging helical CT combines the known advantages of dynamic CT in this clincial situation with the general advantages described previously for a helica CT scan. It is particularly useful when looking at areas such as the ribs, sternum or shoulder or areas that are different to evaluate because of degrees of obliquity of the underlying skeletal structure. Helical CT is also useful in looking at bening tumors e.g. the combination of marrow collimation and small interscan space allowing indus detection in even the most subtle changes of osteoid osteoma. helical CT scanning in these cases may be used to guide percutaneous resection on the lesion. Musculoskeletal oncologic imaging also is aided by MPR & 3-D reconstruction. MPR provides important localizing information & can define mass shape & size, tumor margins and effect on fascial planes. If bone involvement is suspected - 3-D reconstruction is helpful in making decision between surgery and radiation therapy. Detection of impeding fractures and the realtionship of tumor affected bone to weight bearing zones is defined well on 3-D reconstruction. CT angiography may prove to be valuable as a vascular map for tumor involvement & help to determine resectability.
Application of helical CT It is useful particularly in anatomically complex areas such as the shoulder, wrist, ankle, anlkle & pelvis and in anatomical zones most prone to motion, including the shoulder and wrist.
CT is especially useful in the evaluation fo fractures and dislocation or of the other complex injuries. The use of 3-D reconstruction allows full documentation of abnormalities not seen well on other radiography studies including glenohumoral trauma, pseudosubleuxation & scapular and sternoclavicular abnormalities.
CT arthrography has numerous application in painful shoulder :
CT scan is a valuable adjacent to plain radiography in the evaluation of the traumatized adult elbow. CT scan is indicated in many clinical scenarios. 1. Severe or complex injuries. 2. When foreign bodies are present. 3. Following elbow joint dislocation. 4. When pain is preventing positioning for radiography. 5. When subtle fractures is casted elbows is to be evaluated. 6. When an effusion is seen or plain films without any visible fracture. Helical CT is very useful in evaluating elbow trauma as seen time is less & there is minimal motion artefacts.
MPR and 3-D reconstruciton can separate pylon and other fractures into those requiring acute reduction and those requiring delayed definitive arthroplasty. Coronal and sagittal views are optimal for defining the intergrity of the ankle mortise. Helical CT also is the technique of choice for the evaluation of calcaneal fractures. Reconstruction into coronal and sagittal views in critical for mapping calcaneal fractures. Sternoclavicular joint trauma Hellical CT is the most accurate for determining the presence of SCJ dislocation and their degree of displacement . In patient with posterior SCJ dislocation , helical CT of mediastinu with iodinated contrast is a must rule out injury of the great vessels. In reducible SCJ dislocation , the medial end of the clavicle may be seen in normal position.If SCJ dislocation is suspected the patient should asked to rotate the affected arm internally.
Sagittal and oblique reconstruction are useful for defining subtle displacements and fracture mapping. MPR alone or in conjugation with helical CT myelography has a wide variety of application including the detection of fracture , subluxation, locked facets and foreign bodies. The 3-D edit function is useful in spinal trauma as a vertebral body end plates and trabecular pattern can be closely evaluated.
Helical CT can evaluate occult or complex fractures , abcess healing fractures and evaluate post surgical wrist.The helical CT imaging can involve axial, coronal, saggital or long axis of scaphoid planes. Two planes are generally required and at least one should be perpendicular to the area of interest.
MRI is the standard of care in imaging the painful knee . CT remains useful in acute trauma setting where it is more sensitive for bones than MRI.Helical CT with sagittal and coronal reformatting evaluates tibial plateau injuries fastest with minimal patient discomfort. The extent of plateau depression is defined best on a reformatted sagittal view. Helical CT is the examination of choice for dislocation of the proximal tibiofibular joint.The integrity of the cruciate ligaments and menisci may be studied by CT but this requires intra-articular contrast injection. These structures are best evaluated by MRI.
Helical CT is valuable particularly in detecting subtle acetabular fractures or the intra-articular joint fragments because these calcified fragments cannot be adequately visualised with MRI. It is an essential study for management and operative planning .It provides excellent detail of the of the bony pelvis, allows good contrast resolution and details the relative location of the fracture. MRPs particularly in this coronal, saggital and oblique planes are important to determine the management of acetabular fracture. For presurgical planning , procedure approach and screw placement 3-D reconstructions are very useful.The 3-D formation has several advantages:- 1. Less radiation when compared with the normal approach of performing both plain radiographs and helical CT. 2. The selection of optimal rather than arbitrary projections. 3. Elimination of suboptimal radiographic exposures,difficult patient positionings and bowel artefacts. Musculoskeletal infection and inflammation Musculoskeletal infection are increasing owing to the increase in the number of immuno compromised patients who are prone to wide range of infectin. The main aim here is to determine the presence or absence of infectin or inflammation to determinal the presence of gas or associated bony abnormalities, to determine which tissue compartments are involved & to make spcific diagosis of disease procers. MRI is useful for soft tissue evaluation but spiral CT has advantage in the alnte setting it also includes lower post, faster scanning & relative case of examination. Sign of soft tissue inflammation on spiral CT are -
The helical CT can be helpful in following ways. 1. Confirm or suggest cellutitis. 2. Detecting abcess, fascitis or hyohecrosis even when not clinically suspected. 3. Ostemyelitis hecial CT can be an important adjuct to MRI & bone scanning.
The general goals of oncologic imaging are :
Vascularity of lesions is defined well on helical CT because of the high level of circulating contrast even when large areas are being scanned & tumor matrix if present is detected eastly. helcial CT may be helpful in distinguishing myositis ossification from primary muscle tumor. Congenital and acquired musculoskeletal lesion. The helical CT can be helpful in the following conditions. 1. Congenital dysplasia of hip. 2. Avascular necrosis of femoral head. 3. Coalition. 4. Skeletal dysplasia (e.g turne's asphyxiating thoracic dysplasia) |
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Advantages
of Helical (Spiral C.T) C.T