Radiographic Metrics Research Articles

Measuring spine fracture outcomes: Common scales and checklists

Introduction Although outcome instruments have been used extensively in spine surgical research, few studies at present specifically address their use in investigations regarding spine trauma. In this review we provide a summary of the outcome instruments used most frequently in spine trauma research, identify the unique challenges of studying outcomes of spine trauma patients, and propose an integrated approach that may be beneficial for future studies. Methods We reviewed the use of outcome instruments applicable to spine trauma research, including generic health measures, inventories of back-specific function, pain scales, health related quality of life (HRQOL) instruments, and radiographic determinants of outcome. Results Several inventories have been utilised to measure clinical outcomes following spinal trauma. Excluding measures of neurological function (e.g. ASIA motor score), none have been specifically validated for use with spine fractures. The SF-36, RMDQ, and ODI are amongst the most commonly used instruments. Importantly, the use of validated functional outcome measures in spine trauma research is hampered by the fact that the pre-morbid state of patients who sustain spine trauma may not be accurately represented by normative values established for the general population. The VAS is used most frequently to assess degree of neck and back pain. Most studies have relied on non-validated measures to determine radiographic results of treatment, although more elegant radiographic metrics exist. Conclusions Functional outcome measurement of traumatically injured spine patients is challenging because available generic and spine-specific instruments were not designed for or validated in this population. Furthermore, no single inventory is capable of capturing global data necessary to evaluate results following these injuries. Investigations seeking to quantify outcomes following spine trauma should consider the use of a combination of existing surveys in a complementary fashion that should include a generic health survey, a measure of back-specific function, and determinants of bodily pain and work-related disability.

WE-C-304A-06: Computed Radiography Image Exposure Revisited and Case Study

Purpose: To provide case studies for computed radiographic(CR) system image exposure measurement metrics and drive manufacture innovation. Methods and Materials:Computed radiographyimage plate exposure indices were monitored over time. For entries in the exposure log file that indicated more than five times of the usual value, time stamps in the entries were matched manually to images stored on PACS to identify possible causes. Results: Large variation in the values of the exposure index was found. Both operator errors and software failures were found for images of high value of exposure index. After corrective actions, the FWHM of the distribution of the exposure index has decreased although the range of the value remains the same. Cases from Pediatric Intensive Care Unit are the most difficult to handle because of the patient size and medical complications. Conflict of Interest (only if applicable): JL is an employee of Agfa HealthCare Corporation

MO-D-332-02: A Formulism Towards Clinically Relevant Radiographic Imaging Metrics in the Presence of Patient Build-Up, Scatter and Attenuation: CMTF, CNPS, and CDQE

Purpose: We present a formulism to extend conventional radiographic metrics: modulation transfer function(MTF),noise power spectrum (NPS) and detective quantum efficiency (DQE), to clinically equivalent analogues: cMTF, cNPS and cDQE, that include patient specific influences of scatter and beam attenuation. We also propose a clinical interpretation of the above metrics: clinical resolution index (CRI), clinical noise index (CNI) and clinical contrast index (CCI), in which a clinical confidence level of resolution, noise and contrast is predicted for a given anatomical structure and geometry. Method and Materials: The formulation and validation of our clinical metrics were conducted on an Elekta iViewGT portal imager. We used a bar‐pattern to evaluate MTF as a function of spatial frequency (f), build‐up (b) and scatter depth (s) within 30 cm thickness of water to obtain cMTF(f,b,s). Uniform flat‐fields through 30 cm thickness of water containing varying attenuating media indicated by mass thickness (δt), a reasonable approximation for Compton limited megavoltage imaging, were used to measure cNPS(f,δt). Finally, cDQE(f,b,s,δt) was computed and normalized by the exit fluence associated with the attenuated fields. Clinical confidence indices for delineating anatomical structures (CRI, CNI and CCI) were obtained by expressing cMTF, cNPS and cDQE as a function of radiographic object size (w = 0.5/f), along with calibrated charts providing the transformation from anatomical size or form to the radiographic size marker (w). Results: Major differences were observed between conventional MTF, NPS and DQE measurements and our clinical equivalents (cMTF, cNPS and cDQE) that reflected the significant influence of patient attenuation and scatter. CRI, CNI and CCI curves were established for several selected anatomical sites that included bony as well as soft tissuecontrast.Conclusion: The clinically equivalent imaging metrics described above provide a significant link between conventional radiographic metrics defined for idealized systems and realistic clinical image quality.

SU‐GG‐I‐115: Characterization of Clinical CBCT and MVCT Systems Based On Fundamental MTF, NPS and DQE Measurements Using a Conventional CatPhan Phantom

Purpose: In image guided radiation therapy (IGRT), the performance of image guidance modalities like kilovoltage cone‐beam computed tomography (CBCT) and megavoltage computed tomography (MVCT) systems is qualitatively verified with a vendor‐provided CatPhan phantom. For a more meaningful QA tool, a methodology to use CatPhan phantoms for fundamental measurements of modulation transfer function (MTF), noise power spectrum (NPS) and detective quantum efficiency (DQE) for CBCT and MVCT systems is presented. Method and Materials: We have extended the method of using bar‐pattern line‐pairs for MTF measurement (that we recently validated for megavoltage imaging) to CBCT and MVCT imagers by using line‐pair inserts within the CatPhan for axial plane MTF measurement. The MTF was also obtained by evaluating a point response from a tungsten carbide bead insert to validate our method. Axial slices representing homogenous water‐equivalent regions of the CatPhan were used to measure NPS that along with the MTF was used to compute DQE. The photon fluence contribution to each slice of the CatPhan was estimated from ion‐chamber dose measurements in a water phantom for identical image settings and Monte Carlo simulation based fluence — dose factors. Phantom set‐up was typically completed within a minute and all analyses were conducted by an automated software program within seconds. Results: Good agreement was observed between MTF curves obtained from the bar‐pattern and point response methods. Our CatPhan based QA methodology was applied to a Varian Trilogy CBCT system as well as a Hi‐ Art Tomotherapy unit. Conclusion: CatPhan based MTF, NPS and DQE measurements for CBCT and MVCT QA present several advantages including simplicity, speed and the use of widely acclaimed radiographic metrics. They can be easily extended to quantify several factors that affect image quality (beam settings, filtering, sampling, reconstruction, field size, etc).