Radiation exposure from musculoskeletal computerized tomographic scans

Theoretical increase of thyroid cancer induction from cervical spine multidetector computed tomography in pediatric trauma patients

BACKGROUND

The trend of increasing cervical spine multidirectional computed tomography (MDCT) imaging of pediatric trauma patients is characteristic of the overall dramatic increase in computed tomography utilization in the United States. The purpose of this study is to compare the amount of radiation a pediatric trauma patient absorbs to the thyroid from plain radiographs and MDCT of the cervical spine and to express risk by calculation of theoretical thyroid cancer induction.

METHODS

A retrospective evaluation of pediatric trauma patients admitted from October 1, 2004, to October 31, 2009, was performed at an academic, Level I trauma center. Inclusion criteria were Level I/II trauma patients, cervical spine imaging performed at our institution, and age <18 years. Absorbed thyroid radiation was calculated for patients receiving plain radiographs or MDCT. Thyroid cancer risk was calculated using the 2006 Biological Effects on Ionizing Radiation VII report.

RESULTS

Six hundred seventeen patients met inclusion criteria: 224 received cervical spine radiographs and 393 received cervical spine MDCT. The mean thyroid radiation absorbed from radiographs was 0.90 mGy for males and 0.96 mGy for females compared with 63.6 mGy (males) and 64.2 mGy (females) receiving MDCT (p < 0.001). The median excess relative risk of thyroid cancer induction from one cervical spine MDCT in males was 13.0% and females was 25.0%, compared with 0.24% (males) and 0.51% (females) for radiographs (p < 0.001).

CONCLUSIONS

The significant difference in radiation that MDCT delivers to the pediatric trauma patient when compared with plain radiographs should temper routine use of computed tomography in pediatric cervical spine clearance algorithms.

Clinical indications for arterial imaging in cervical trauma

STUDY DESIGN

A retrospective cohort study.

OBJECTIVE

To evaluate the clinical indications for acquiring arterial imaging in cervical trauma.

SUMMARY OF BACKGROUND DATA

Cervical spine injuries are very common in high-energy trauma and are frequently seen at Level I trauma centers across the country. A clinical standard of care does not exist to indicate when further evaluation of the cervical vasculature is warranted after a documented cervical spine injury.

METHODS

After institutional review board approval, a retrospective study combining the data from 2 Level I trauma centers was undertaken. An evaluation of every arterial imaging procedure (computed tomography and magnetic resonance angiography) of the cervical spine was collected to further delineate indications and outcomes of these imaging modalities.

RESULTS

From 2005 to 2009, there were a total of 159 patients who underwent cervical arterial imaging at the 2 participating institutions for the indication of cervical trauma with concern for arterial injury. Thirty-six (22.64%) were found to have an injury after arterial imaging. There was a statistically significant correlation with displaced cervical injuries (P < 0.0153), which were defined as cervical dissociations or perched and/or jumped facets. The other statistically significant correlation was the presence of a neurological deficit (P < 0.001), defined as any presenting deficit on sensory or motor examination. Level of injury defined as axial (O-C2) versus subaxial (C3-C7), age, body mass index, and history of cigarette smoking were not statistically related to vascular injury.

CONCLUSION

Our retrospective evaluation indicates that there should be a lower threshold for obtaining arterial imaging with cervical injury patterns historically known to compromise the vasculature, which also have concomitant displaced cervical spine injuries and/or a neurological deficit.

3D morphometric analysis of 43 scapulae

BACKGROUND

Accurate knowledge of the scapular anatomy is fundamental for the preoperative evaluation but some bony landmarks are difficult to identify. Statistical approaches based on subject-specific parametric models could be used to overcome this difficulty. The aim of this study was to propose a quantitative parametric model of the scapula and to analyze correlations between descriptive morphologic parameters.

MATERIALS AND METHODS

Forty-three scapulae were scanned and reconstructed. Each 3D scapula was regionalized and a simple geometric element was best fitted on each region using least square method. Descriptive parameters of each region were obtained. Correlation and linear regression analyses were performed between all measurements in order to assess parameters that can be used as predictors of the other descriptive parameters.

RESULTS

Morphometric scapular measurements from 3D reconstructions were obtained. Correlation and linear regression analyses assessed correlations between the glenoid width and both the glenoid height and the acromial width. Also, we obtained correlation between the orientation of the inferior part of the acromion on the A-P view and on the axillary view.

DISCUSSION

Parametric models are widely used in biomechanics for identifying anatomical landmarks or rotations centers of these structures. For the scapula, no such model is available. We elaborated a first parametric model of scapula based on a large database of 43 scapulae. Our morphometric measurements are very close to others founded in literature. Correlations obtained should help to progress toward relevant subject-specific models of the scapula based on reduced information.

Evaluation of the effect of computed tomography scan protocols and freeform fabrication methods on bone biomodel accuracy

OBJECTIVE

To assess the effect of computed tomography (CT) scan protocols (radiation amounts) and fabrication methods on biomodel accuracy and variability.

SAMPLE

Cadaveric femur of a Basset Hound.

PROCEDURES

Retroreconstructions (n = 158) were performed of 16 original scans and were visually inspected to select 17 scans to be used for biomodel fabrication. Biomodels of the 17 scans were made in triplicate by use of 3 freeform fabrication processes (stereolithography, fused deposition modeling, and 3-D printing) for 153 models. The biomodels and original bone were measured by use of a coordinate measurement machine.

RESULTS

Differences among fabrication methods accounted for 2% to 29% of the total observed variation in inaccuracy and differences among method-specific radiation configurations accounted for 4% to 44%. Biomodels underestimated bone length and width and femoral head diameter and overestimated cortical thickness. There was no evidence of a linear association between thresholding adjustments and biomodel accuracy. Higher measured radiation dose led to a decrease in absolute relative error for biomodel diameter and for 4 of 8 cortical thickness measurements.

CONCLUSIONS AND CLINICAL RELEVANCE

The outside dimensions of biomodels have a clinically acceptable accuracy. The cortical thickness of biomodels may overestimate cortical thickness. Variability among biomodels was caused by model fabrication reproducibility and, to a lesser extent, by the radiation settings of the CT scan and differences among fabrication methods.

Computed tomography evaluation of the femoral and tibial attachments of the posterior cruciate ligament in vitro

PURPOSE

The optimal technique for reconstruction of the posterior cruciate ligament (PCL) is controversial. Regardless of surgical technique and graft choice, anatomic graft placement is essential for successful outcome. The purpose of this study is to evaluate the size and location of the insertions of the PCL using a computed tomography (CT) protocol.

METHODS

The insertions in ten knees were marked in vitro with plastic markers. The CT examination was performed with the knee in extension. On the femur, the position of the center of the insertion site was evaluated relative to Blumensaat's line and the anterior articular surface. On the tibia, the location of the center of the insertion site was described relative to the borders of the tibial plateau and the retrospinal surface.

RESULTS

The surface area of the femoral insertion measured 232 mm(-2) and was centered 8.9 mm from the roof of the intercondylar notch and 18.7 mm from the anterior articular cartilage surface. The surface area of the tibial insertion was 155 mm(2) and was centered 9.1 mm from the posterior border of the tibia on the retrospinal surface, 1.6 mm inferior to the plane of the tibial articular surface. This point was on average 49% of the way across the plateau relative to the medial edge of the plateau and 87% of the way across the plateau relative to the anterior edge.

CONCLUSIONS

Computed tomography can provide detailed localization of the PCL attachment sites on the femur and tibia. Radiation exposure and cost may preclude routine use.

Cyst-like lesions in finger joints detected by conventional radiography: comparison with 320-row multidetector computed tomography

OBJECTIVE

Many rheumatologists and radiologists routinely assess conventional radiographs of the hands, and it is often unclear how to proceed if radiography reveals only cyst-like lesions (CLLs), with otherwise normal findings. The present study was undertaken to evaluate the use of 320-row multidetector computed tomography (MDCT) of the hands in the further assessment of CLLs of metacarpophalangeal (MCP) and proximal interphalangeal (PIP) joints identified on conventional radiography.

METHODS

MCP and PIP joints (n = 1,120 joints) of 56 consecutive patients (44 women [mean age 55 years, range 31-72 years] and 12 men [mean age 57 years, range 37-77 years]) were prospectively scored for the presence of cysts, CLLs, and erosions of the PIP and MCP joints, first on conventional radiographs, then on MDCT. Scoring was performed by 2 independent readers under blinded conditions. Intraclass correlation coefficients were calculated.

RESULTS

By conventional hand radiography, 13 patients (total of 260 joints assessed) were identified as having CLLs in 1 or more joints (total of 36 joints [11 PIP and 25 MCP]). By MDCT, the findings in 19 of 36 joints (53%) were diagnosed as erosions, while 7 of 36 (19%) were confirmed as true cysts, and 10 joints (28%) were normal (false positive). Among the patients with CLLs, 10 of 224 joints with no abnormality seen radiographically had erosions as seen on MDCT. Interreader agreement for erosions was 0.854 (95% confidence interval [95% CI] 0.831-0.874) by conventional hand radiography and 0.952 (95% CI 0.943-0.959) by MDCT.

CONCLUSION

Our results indicate that radiographic appearance of cyst-like lesions may actually represent erosions and should lead to initiation of further imaging tests.

A dedicated cone-beam CT system for musculoskeletal extremities imaging: design, optimization, and initial performance characterization

PURPOSE

This paper reports on the design and initial imaging performance of a dedicated cone-beam CT (CBCT) system for musculoskeletal (MSK) extremities. The system complements conventional CT and MR and offers a variety of potential clinical and logistical advantages that are likely to be of benefit to diagnosis, treatment planning, and assessment of therapy response in MSK radiology, orthopaedic surgery, and rheumatology.

METHODS

The scanner design incorporated a host of clinical requirements (e.g., ability to scan the weight-bearing knee in a natural stance) and was guided by theoretical and experimental analysis of image quality and dose. Such criteria identified the following basic scanner components and system configuration: a flat-panel detector (FPD, Varian 3030+, 0.194 mm pixels); and a low-power, fixed anode x-ray source with 0.5 mm focal spot (SourceRay XRS-125-7K-P, 0.875 kW) mounted on a retractable C-arm allowing for two scanning orientations with the capability for side entry, viz. a standing configuration for imaging of weight-bearing lower extremities and a sitting configuration for imaging of tensioned upper extremity and unloaded lower extremity. Theoretical modeling employed cascaded systems analysis of modulation transfer function (MTF) and detective quantum efficiency (DQE) computed as a function of system geometry, kVp and filtration, dose, source power, etc. Physical experimentation utilized an imaging bench simulating the scanner geometry for verification of theoretical results and investigation of other factors, such as antiscatter grid selection and 3D image quality in phantom and cadaver, including qualitative comparison to conventional CT.

RESULTS

Theoretical modeling and benchtop experimentation confirmed the basic suitability of the FPD and x-ray source mentioned above. Clinical requirements combined with analysis of MTF and DQE yielded the following system geometry: a -55 cm source-to-detector distance; 1.3 magnification; a 20 cm diameter bore (20 x 20 x 20 cm3 field of view); total acquisition arc of -240 degrees. The system MTF declines to 50% at -1.3 mm(-1) and to 10% at -2.7 mm(-1), consistent with sub-millimeter spatial resolution. Analysis of DQE suggested a nominal technique of 90 kVp (+0.3 mm Cu added filtration) to provide high imaging performance from -500 projections at less than -0.5 kW power, implying -6.4 mGy (0.064 mSv) for low-dose protocols and -15 mGy (0.15 mSv) for high-quality protocols. The experimental studies show improved image uniformity and contrast-to-noise ratio (without increase in dose) through incorporation of a custom 10:1 GR antiscatter grid. Cadaver images demonstrate exquisite bone detail, visualization of articular morphology, and soft-tissue visibility comparable to diagnostic CT (10-20 HU contrast resolution).

CONCLUSIONS

The results indicate that the proposed system will deliver volumetric images of the extremities with soft-tissue contrast resolution comparable to diagnostic CT and improved spatial resolution at potentially reduced dose. Cascaded systems analysis provided a useful basis for system design and optimization without costly repeated experimentation. A combined process of design specification, image quality analysis, clinical feedback, and revision yielded a prototype that is now awaiting clinical pilot studies. Potential advantages of the proposed system include reduced space and cost, imaging of load-bearing extremities, and combined volumetric imaging with real-time fluoroscopy and digital radiography.

The effect of CT dose on glenohumeral joint congruency measurements using 3D reconstructed patient-specific bone models

The study of joint congruency at the glenohumeral joint of the shoulder using computed tomography (CT) and three-dimensional (3D) reconstructions of joint surfaces is an area of significant clinical interest. However, ionizing radiation delivered to patients during CT examinations is much higher than other types of radiological imaging. The shoulder represents a significant challenge for this modality as it is adjacent to the thyroid gland and breast tissue. The objective of this study was to determine the optimal CT scanning techniques that would minimize radiation dose while accurately quantifying joint congruency of the shoulder. The results suggest that only one-tenth of the standard applied total current (mA) and a pitch ratio of 1.375:1 was necessary to produce joint congruency values consistent with that of the higher dose scans. Using the CT scanning techniques examined in this study, the effective dose applied to the shoulder to quantify joint congruency was reduced by 88.9% compared to standard clinical CT imaging techniques.

Clinically applied CT arthrography to measure the sulphated glycosaminoglycan content of cartilage

OBJECTIVE

Similar to delayed gadolinium enhanced MRI of cartilage, it might be possible to image cartilage quality using CT arthrography (CTa). This study assessed the potential of CTa as a clinically applicable tool to evaluate cartilage quality in terms of sulphated glycosaminoglycan content (sGAG) and structural composition of the extra-cellular matrix (ECM).

METHODS

Eleven human cadaveric knee joints were scanned on a clinical CT scanner. Of each knee joint, a regular non-contrast CT (ncCT) and an ioxaglate injected CTa scan were performed. Mean X-ray attenuation of both scans was compared to identify contrast influx in seven anatomical regions of interest (ROIs). All ROIs were rescanned with contrast-enhanced μCT, which served as the reference standard for sGAG content. Mean X-ray attenuation from both ncCT and CTa were correlated with μCT results and analyzed with linear regression. Additionally, residual values from the linear fit between ncCT and μCT were used as a covariate measure to identify the influence of structural composition of cartilage ECM on contrast diffusion into cartilage in CTa scans.

RESULTS

CTa resulted in higher X-ray attenuation in cartilage compared to ncCT scans for all anatomical regions. Furthermore, CTa correlated excellent with reference μCT values (sGAG) (R=0.86; R(2)=0.73; P<0.0001). When corrected for structural composition of cartilage ECM, this correlation improved substantially (R=0.95; R(2)=0.90; P<0.0001).

CONCLUSIONS

Contrast diffusion into articular cartilage detected with CTa correlates with sGAG content and to a lesser extent with structural composition of cartilage ECM. CTa may be clinically applicable to quantitatively measure the quality of articular cartilage.

Task-based modeling and optimization of a cone-beam CT scanner for musculoskeletal imaging

PURPOSE

This work applies a cascaded systems model for cone-beam CT imaging performance to the design and optimization of a system for musculoskeletal extremity imaging. The model provides a quantitative guide to the selection of system geometry, source and detector components, acquisition techniques, and reconstruction parameters.

METHODS

The model is based on cascaded systems analysis of the 3D noise-power spectrum (NPS) and noise-equivalent quanta (NEQ) combined with factors of system geometry (magnification, focal spot size, and scatter-to-primary ratio) and anatomical background clutter. The model was extended to task-based analysis of detectability index (d') for tasks ranging in contrast and frequency content, and d' was computed as a function of system magnification, detector pixel size, focal spot size, kVp, dose, electronic noise, voxel size, and reconstruction filter to examine trade-offs and optima among such factors in multivariate analysis. The model was tested quantitatively versus the measured NPS and qualitatively in cadaver images as a function of kVp, dose, pixel size, and reconstruction filter under conditions corresponding to the proposed scanner.

RESULTS

The analysis quantified trade-offs among factors of spatial resolution, noise, and dose. System magnification (M) was a critical design parameter with strong effect on spatial resolution, dose, and x-ray scatter, and a fairly robust optimum was identified at M ∼ 1.3 for the imaging tasks considered. The results suggested kVp selection in the range of ∼65-90 kVp, the lower end (65 kVp) maximizing subject contrast and the upper end maximizing NEQ (90 kVp). The analysis quantified fairly intuitive results-e.g., ∼0.1-0.2 mm pixel size (and a sharp reconstruction filter) optimal for high-frequency tasks (bone detail) compared to ∼0.4 mm pixel size (and a smooth reconstruction filter) for low-frequency (soft-tissue) tasks. This result suggests a specific protocol for 1 × 1 (full-resolution) projection data acquisition followed by full-resolution reconstruction with a sharp filter for high-frequency tasks along with 2 × 2 binning reconstruction with a smooth filter for low-frequency tasks. The analysis guided selection of specific source and detector components implemented on the proposed scanner. The analysis also quantified the potential benefits and points of diminishing return in focal spot size, reduced electronic noise, finer detector pixels, and low-dose limits of detectability. Theoretical results agreed quantitatively with the measured NPS and qualitatively with evaluation of cadaver images by a musculoskeletal radiologist.

CONCLUSIONS

A fairly comprehensive model for 3D imaging performance in cone-beam CT combines factors of quantum noise, system geometry, anatomical background, and imaging task. The analysis provided a valuable, quantitative guide to design, optimization, and technique selection for a musculoskeletal extremities imaging system under development.

The effect of decreasing computed tomography dosage on radiostereometric analysis (RSA) accuracy at the glenohumeral joint

Standard, beaded radiostereometric analysis (RSA) and markerless RSA often use computed tomography (CT) scans to create three-dimensional (3D) bone models. However, ethical concerns exist due to risks associated with CT radiation exposure. Therefore, the aim of this study was to investigate the effect of decreasing CT dosage on RSA accuracy. Four cadaveric shoulder specimens were scanned using a normal-dose CT protocol and two low-dose protocols, where the dosage was decreased by 89% and 98%. 3D computer models of the humerus and scapula were created using each CT protocol. Bi-planar fluoroscopy was used to image five different static glenohumeral positions and two dynamic glenohumeral movements, of which a total of five static and four dynamic poses were selected for analysis. For standard RSA, negligible differences were found in bead (0.21±0.31mm) and bony landmark (2.31±1.90mm) locations when the CT dosage was decreased by 98% (p-values>0.167). For markerless RSA kinematic results, excellent agreement was found between the normal-dose and lowest-dose protocol, with all Spearman rank correlation coefficients greater than 0.95. Average root mean squared errors of 1.04±0.68mm and 2.42±0.81° were also found at this reduced dosage for static positions. In summary, CT dosage can be markedly reduced when performing shoulder RSA to minimize the risks of radiation exposure. Standard RSA accuracy was negligibly affected by the 98% CT dose reduction and for markerless RSA, the benefits of decreasing CT dosage to the subject outweigh the introduced errors.

Minimally invasive scoliosis surgery: an innovative technique in patients with adolescent idiopathic scoliosis

Minimally invasive spine surgery is becoming more common in the treatment of adult lumbar degenerative disorders. Minimally invasive techniques have been utilized for multilevel pathology, including adult lumbar degenerative scoliosis. The next logical step is to apply minimally invasive surgical techniques to the treatment of adolescent idiopathic scoliosis (AIS). However, there are significant technical challenges of performing minimally invasive surgery on this patient population. For more than two years, we have been utilizing minimally invasive spine surgery techniques in patients with adolescent idiopathic scoliosis. We have developed the present technique to allow for utilization of all standard reduction maneuvers through three small midline skin incisions. Our technique allows easy passage of contoured rods, placement of pedicle screws without image guidance, and allows adequate facet osteotomy to enable fusion. There are multiple potential advantages of this technique, including: less blood loss, shorter hospital stay, earlier mobilization, and relatively less pain and need for pain medication. The operative time needed to complete this surgery is longer. We feel that a minimally invasive approach, although technically challenging, is a feasible option in patients with adolescent idiopathic scoliosis. Although there are multiple perceived benefits, long term data is needed before it can be recommended for routine use.

Calculating the mounting parameters for Taylor Spatial Frame correction using computed tomography

The Taylor Spatial Frame uses a computer program-based six-axis deformity analysis. However, there is often a residual deformity after the initial correction, especially in deformities with a rotational component. This problem can be resolved by recalculating the parameters and inputting all new deformity and mounting parameters. However, this may necessitate repeated x-rays and delay treatment. We believe that error in the mounting parameters is the main reason for most residual deformities. To prevent these problems, we describe a new calculation technique for determining the mounting parameters that uses computed tomography. This technique is especially advantageous for deformities with a rotational component. Using this technique, exact calculation of the mounting parameters is possible and the residual deformity and number of repeated x-rays can be minimized. This new technique is an alternative method to accurately calculating the mounting parameters.

Use of intraoperative computed tomography scanning in determining the magnitude of arthroscopic osteochondroplasty

Femoroacetabular impingement has recently become a recognized cause of disability and hip arthritis. Hip arthroscopy and femoroacetabular reshaping have been performed to treat this condition. Quantification of the excess femoral and acetabular bone requiring resection has been challenging with the less invasive arthroscopic technique. We describe the use of intraoperative computed tomography assessing osteochondroplasty during arthroscopic surgery to treat cam- and pincer-type femoroacetabular impingement. We also describe the technical steps and present the important radiologic findings we have been able to visualize. We found intraoperative computed tomography scanning to be a reliable and reproducible method of assessing the quality of femoroacetabular impingement surgery. We believe that femoroacetabular impingement surgery can be assessed intraoperatively by use of computed tomography scanning where corrections can be made if necessary.

Validation of a noninvasive technique to precisely measure in vivo three-dimensional cervical spine movement

STUDY DESIGN

In vivo validation during functional loading.

OBJECTIVE

To determine the accuracy and repeatability of a model-based tracking technique that combines subject-specific computed tomographic (CT) models and high-speed biplane x-ray images to measure three-dimensional (3D) in vivo cervical spine motion.

SUMMARY OF BACKGROUND DATA

Accurate 3D spine motion is difficult to obtain in vivo during physiological loading because of the inability to directly attach measurement equipment to individual vertebrae. Previous measurement systems were limited by two-dimensional (2D) results and/or their need for manual identification of anatomical landmarks, precipitating unreliable and inaccurate results. All previous techniques lack the ability to capture true 3D motion during dynamic functional loading.

METHODS

Three subjects had 1.0-mm-diameter tantalum beads implanted into their fused and adjacent vertebrae during anterior cervical discectomy and fusion surgery. High-resolution CT scans were obtained after surgery and used to create subject-specific 3D models of each cervical vertebra. Biplane x-ray images were collected at 30 frames per second while the subjects performed flexion/extension and axial rotation movements 6 months after surgery. Individual bone motion, intervertebral kinematics, and arthrokinematics derived from dynamic radiostereophotogrammetric analysis served as a gold standard to evaluate the accuracy of the model-based tracking technique.

RESULTS

Individual bones were tracked with an average precision of 0.19 and 0.33 mm in nonfused and fused bones, respectively. Precision in measuring 3D joint kinematics in fused and adjacent segments averaged 0.4 mm for translations and 1.1° for rotations, while anterior and posterior disc height above and below the fusion were measured with a precision ranging between 0.2 and 0.4 mm. The variability in 3D joint kinematics associated with tracking the same trial repeatedly was 0.02 mm in translation and 0.06° in rotation.

CONCLUSION

The 3D cervical spine motion can be precisely measured in vivo with submillimeter accuracy during functional loading without the need for bead implantation. Fusion instrumentation did not diminish the accuracy of kinematic and arthrokinematic results. The semiautomated model-based tracking technique has excellent repeatability.

CT reveals a high incidence of osseous abnormalities in hips with labral tears

BACKGROUND

Acetabular labral tears are being diagnosed with increasing frequency and there is a growing consensus that these tears rarely occur in the absence of osseous abnormalities.

QUESTIONS/PURPOSES

We therefore determined the presence of structural abnormalities in patients with acetabular labral tears using a standardized CT protocol.

METHODS

We evaluated 135 consecutive patients with labral tears diagnosed by MRI with CT scans of the symptomatic hip. The CT scans were evaluated in a standardized fashion to determine acetabular and femoral pathomorphologic features. Acetabular evaluation included version measurements and anterior and lateral center-edge angles. Femoral parameters evaluated included version, alpha angle, and neck-shaft angle.

RESULTS

One hundred twenty-two (90%) of the 135 hips had structural abnormalities. One hundred two (76%) had an alpha angle greater than 50°, 18 (13%) had femoral version less than 5°, 22 (16%) had femoral version greater than 25º, and five (4%) had coxa valga. Fifty-eight (43%) patients had acetabular retroversion and five (4%) had a lateral center-edge angle less than 20º. Of the 58 patients with acetabular retroversion, 23 had isolated cranial retroversion, 12 had isolated central retroversion, and 23 had combined cranial and central retroversion. Sixty-seven of the 121 hips (55%) with bony abnormalities had a combination of abnormalities.

CONCLUSIONS

Ninety percent of patients with labral tears had structural abnormalities seen on CT scans. These structural abnormalities frequently occur in combination, and understanding these underlying morphologic features of the hip can help guide treatment.

LEVEL OF EVIDENCE

Level IV, diagnostic study. See Guidelines for Authors for a complete description of levels of evidence.

Technical aspects of CT imaging of the spine

This review article discusses technical aspects of computed tomography (CT) imaging of the spine. Patient positioning, and its influence on image quality and movement artefact, is discussed. Particular emphasis is placed on the choice of scan parameters and their relation to image quality and radiation burden to the patient. Strategies to reduce radiation burden and artefact from metal implants are outlined. Data acquisition, processing, image display and steps to reduce artefact are reviewed. CT imaging of the spine is put into context with other imaging modalities for specific clinical indications or problems. This review aims to review underlying principles for image acquisition and to provide a rough guide for clinical problems without being prescriptive. Individual practice will always vary and reflect differences in local experience, technical provisions and clinical requirements.