abnormal spinal curvature may be idiopathic or secondary to dystrophic etiologies , such as congenital , traumatic , and malignant causes .
initial assessment and followup of patients with an abnormal spinal curvature have routinely been performed using plain radiographs . to evaluate dystrophic features , magnetic resonance imaging ( mri )
computed tomography ( ct ) is proving to be of benefit in the assessment of patients with an abnormal spinal curvature [ 410 ] .
recent advances in multidetector ct ( mdct ) technique allow the evaluation of the spine in multiple 2-d planes ( figures 1(a ) and 2(a ) ) and with a three - dimensional volume - rendered series ( 3-d vr ) ( figures 1(b ) and 2(b ) ) .
in addition , the data from the mdct study can also be used to generate a translucent display , a computer - generated image set that provides 3-d images of the spine enabling assessment of surgical instrumentation through the bony structures ( figures 2(c ) and 2(d ) ) . the 3-d vr series , including the translucent display , which are generated by computer manipulation of the axial ct source data without additional radiation , have led to a growth in demand for mdct for the imaging of the spine by the spine surgeons at our institution , a major cancer center . however , to the best of our knowledge , there are no reports in the literature on the use of mdct with the 3-d vr series and the translucent display for evaluation of abnormal spinal curvature , which requires additional time for processing and interpretation .
we tested the hypothesis that the 3-d vr series , including the translucent display , provides additional information beyond that of the 2-d orthogonal mdct in the evaluation of abnormal spinal curvature in patients treated at a cancer center .
the institutional review board of the university of texas md anderson cancer center approved this study and waived the requirements for an informed consent .
mdct studies of the spine in patients who had a history of possible primary or metastatic disease to the spine or neurofibromatosis type 1 and an abnormal spinal curvature greater than 25 degrees , as assessed on mdct , were included in our study .
measurements of spinal curvature were made on the 2-d coronal or sagittal reconstructed ct images , as described in the literature [ 4 , 5 ] .
the review of the imaging studies and clinical data was performed by 3 neuroradiologists ( jmd , lk , and ngt ) in a consensus fashion . the 3-d vr series ,
including translucent display , was compared to the 2-d orthogonal mdct studies without the 3-d vr series in the assessment of the following 3 categories : spinal curvature ; bony definition ( deformity , fusion , and destruction ) ; additional findings ( mass lesions , fractures , and instrumentation ) . for each patient ,
the 3-d vr series was given a score of 1 if it was judged to be 
helpful  in the evaluation of the aforementioned 3 categories ( 48 patients  3 categories = 144 total possible categories ) and a score of 0 if it was  not helpful  .
mdct examinations were performed on a multidetector ct scanner ( ge medical systems ) to yield imaging in the axial plane using the following parameters : 140  kv , 220250  ma , and a 1.25  mm slice thickness .
the mdct examinations were performed without ( n = 41 ) , with ( n = 3 ) , or without and with ( n = 4 ) intravenous contrast ( optiray , mallinckrodt inc . ,
bone algorithm and soft tissue images were available and reviewed in all patients ' mdct studies .
postprocessing was then performed by a trained technologist on an advantage aw4.2 workstation ( ge medical systems ) using volume view software ( ge medical systems ) .
the post - processing provided imaging in the sagittal and coronal planes in all patients , and these images , together with the axial source images , are hereafter referred to as the 2-d orthogonal mdct study .
in addition , 3-d vr images of the spine ( figures 1(b ) and 2(b ) ) and the translucent display ( figures 2(c ) and 2(d ) ) , for patients in whom surgical instrumentation was placed for the stabilization of abnormal spinal curvature , were provided .
the study included 48 patients ( 35 female and 13 male ; ages 1272 , mean age , 48 years ) , as summarized in table 1 .
twenty - four patients had a dextroscoliotic curvature measuring between 26 and 93 degrees ( mean , 45.5 ) , 9 patients had a levoscoliotic curvature measuring between 25 and 72 degrees ( mean , 35.2 degrees ) , and 15 patients had a kyphotic curvature of measuring between 27 and 89 degrees ( mean 48.1 degrees ) .
twenty - six patients had a 3-d vr series without a transparent display and 22 patients had a 3-d vr series with a transparent display .  
the 3-d vr series was rated as  helpful  when compared to the 2-d orthogonal mdct study in 38 of 48 ( 79.2% ) patients ; in 10 of 48 ( 20.8% ) patients , the 3-d vr series was rated as  not helpful  .
helpful  in 63 of 144 ( 43.8% ) total possible categories ( table 2 ) .
this included the assessment of the spinal curvature in 32 of 48 ( 66.7% ) patients , including dextroscoliosis ( n = 16 , 2683 , mean 50.6 ) , levoscoliosis ( n = 8 , 2572 , mean 35.3 ) , and kyphosis ( n = 8 ; 4289 , mean 58.9 ) .
the 3-d vr series was rated as  not helpful  in 16 of 48 patients ( 33.3% ) , including those with dextroscoliosis ( n = 8 ; 2949 , mean 35.4 ) , levoscoliosis ( n = 1 , 35 ) , and kyphosis ( n = 7 ; 2747 , mean 35.7 ) .  
the 3-d vr series was rated as  helpful  in the bone definition category for 14 of 48 ( 29.2% ) patients , including bone deformity ( n = 6 ) , bony fusion ( n = 4 ) , bony destruction ( n = 2 ) , anterolisthesis ( n = 2 ) , and the additional findings category , including surgical instrumentation , in 17 patients , specifically , for the assessment of the fusion rods ( n = 15 ) or an anterior fusion plate and pedicular screws ( n = 2 ) .

 figure 1 shows 2-d orthogonal mdct and 3-d vr images from patient no . 11 , a 16-year - old male who presented with a kyphotic curvature secondary to a recurrent juvenile pilocytic astrocytoma of the thoracic spinal cord .
the 3-d vr images were scored as 1 ,  helpful  in the evaluation of the spinal curvature as the spine is out of plane on 2-d orthogonal mdct imaging . 

4 , a 61-year - old woman who underwent correction of an abnormal spinal curvature at an outside institution .
the patient had a levoscoliotic curvature of the thoracic spine to such a degree the spinal column and instrumentation could not be visualized as one structure on a single , 2-d orthogonal mdct image .
the transparent display was helpful in demonstrating the scoliotic curvature and the position and integrity of the instrumentation .
helpful  in comparison to the corresponding 2-d orthogonal mdct in the assessment of abnormal spinal curvature in 38 of 48 patients , specifically in the evaluation of abnormal curvature in 32 patients , bony definition in 14 patients , and additional findings , including surgical instrumentation , in 17 patients .
these findings confirm our hypothesis that the 3-d vr series , including the translucent display , is of additional benefit in the assessment of abnormal spinal curvature in patients treated at a major cancer center . as not all patients had abnormalities in each of the 3 categories , that is , surgical instrumentation ,
the percentage of cases where the 3-d vr was helpful is likely higher than what we report , further supporting our hypothesis .  
when reviewing an mdct study of abnormal spinal curvature , the 3-d vr series can be assessed before the 2-d orthogonal mdct study . as the spinal deformity in these patients is often out of the plane of imaging on a single , 2-d orthogonal mdct image ( figures 1(a ) and 2(a ) ) , the 3-d vr sequence provides comprehensive assessment of the entire spine on a single 3-d image ; this image can then be rotated and viewed from 360 degrees . in our study , we found this more beneficial in patients with a greater degree of dextroscoliotic than kyphotic curvature and more helpful for a greater degree of abnormal spinal curvature .
not only can the 3-d vr series evaluate the shape of the spine , but also aid in the detection of a rotatory component , anterolisthesis , and the apex of the curvature .
in addition , with the 3-d vr series , the number of vertebral bodies can be counted in a single view ; this assures that the numbering assignment will be correct if an anomalous number of spinal segments are present .
this is more difficult to determine on orthogonal 2-d mdct as the spine is often out of the plane of imaging due to the spinal curvature .
the 3-d vr series can also evaluate the vertebral bodies for evidence of dysplasia , fracture , or bony destruction .
previous authors [ 1012 ] have demonstrated that ct is better than plain radiographs for the evaluation of spine abnormalities .
state that when a complex osseous deformity is present , radiographs are inadequate for complete evaluation and the use of ct is mandatory , especially when surgery is planned .
our result takes this evaluation as a step further and demonstrate that the 3-d vr series would benefit 2-d orthogonal mdct in the evaluation of vertebral anomalies as the 14 studies scored a  helpful 
rating in the evaluation of the bony structures , including 4 cases with prior surgical bony fusion .   in the post - operative patient
, the 3-d vr series with translucent display may be used to assess surgical instrumentation .
this technique allows the visualization of the instrumentation through the bone and can also be rotated and viewed in 360 degrees , including in oblique planes . as the surgical instrumentation is visualized as one component on a single image , and the position and integrity of support rods and pedicular screws are assessed ,
coloring of the spinal instrumentation is also possible ( figure 2(d ) ) . in every case with surgical instrumentation in our study ,
in fact , our referring spine surgeons insist on inclusion of the 3-d vr series for the evaluation of the spine and the transparent display for a comprehensive overview of the surgical instrumentation .
further study can be undertaken to determine if the 3-d vr series with translucent display can be used to evaluate surgical instrumentation following spinal surgery in the general population with an abnormal spinal curvature and to evaluate associated complications .
as recent advances in mdct technology have led to a significant reduction in streak artifact related to metallic hardware [ 13 , 14 ] .
mdct with vr series may lead to better evaluation of the postoperative spine and possibly easier detection of complications .
it should be noted , though , that the interpreting radiologist must be careful not to mistake streak artifact that extends through the surgical instrumentation of the breakage of hardware .  
the purpose of this study was to determine if the 3-d vr images provide additional information to the orthogonal 2-d mdct dataset and the results support our hypothesis .
we are not suggesting that 3-d vr can replace the orthogonal 2-d mdct ; rather 3-d vr is complementary .
one limitation of the study is that this is a very select group of patients , mainly those presenting for treatment of their disease to a major cancer center .  
computed tomography has been described in the measurement of scoliosis , including the rotatory component [ 1519 ] .
further study will be necessary to determine if the 3-d vr series can be for evaluation and measurement of abnormal curvature in the general population , including for idiopathic scoliosis .
one negative aspect of mdct is that patients are imaged in the recumbent position and the use of ionizing radiation .
the downside of patient positioning also applies to the reconstructed 3-d vr series ; however , no addition radiation is necessary for computer generation of the 3-d vr series or the translucent display .
herein , we have illustrated the added benefit of 3-d vr imaging and the translucent display to axial and 2-d orthogonal mdct imaging of the spine for the evaluation of abnormal spinal curvature among patients at a major cancer center .
failure to recognize the etiology of spinal curvature , such as syndromic deformities , fractures , or malignancies of the spine , can affect treatment and management outcomes for patients .
the translucent display series provides a more comprehensive evaluation of surgical instrumentation following correction of an abnormal spinal curvature or resection of malignancy .
it is , therefore , beneficial for spine surgeons and radiologists involved in the care of patients with abnormal spinal curvature to be aware of the benefits of the 3-d vr series and the translucent display .
 
 background . 
 abnormal spinal curvature is routinely assessed with plain radiographs , mdct , and mri . 
 mdct can provide two - dimensional ( 2-d ) orthogonal as well as reconstructed three - dimensional volume - rendered ( 3-d vr ) images of the spine , including the translucent display : a computer - generated image set that enables the visualization of surgical instrumentation through bony structures . 
 we hypothesized that the 3-d vr series provides additional information beyond that of 2-d orthogonal mdct in the evaluation of abnormal spinal curvature in patients evaluated at a major cancer center . 
 methods . 
 the 3-d vr series , including the translucent display , was compared to 2-d orthogonal mdct studies in patients with an abnormal spinal curvature greater than 25 degrees and scored as being not helpful ( 0 ) or helpful ( 1 ) in 3 categories : spinal curvature ; bony definition ; additional findings ( mass lesions , fractures , and instrumentation ) . 
 results . in 38 of 48 ( 79.2% ) patients assessed , the 3-d vr series were scored as helpful in 63 of 144 ( 43.8% ) total possible categories ( 32 spinal curvature ; 14 bony definition ; 17 additional findings ) . 
 conclusion . 
 three - dimensional mdct images , including the translucent display , are complementary to multiplanar 2-d orthogonal mcdt in the evaluation of abnormal spinal curvature in patients treated at a major cancer center . 