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Assessment of digital radiographic detectors and systems using eDQE

RAI Labs is one of a small, but growing, cadre of international research groups with a long-standing focus in image quality metrics of digital radiography systems. As a group, we have made significant contributions to the advancement of image metrology through our critical evaluation of existing metrics and standard methodologies; development and validation of new metrics; and active participation in various national and international initiatives aimed at establishing standardized image quality methodologies for evaluating these systems.


GE Revolution XQ/i

aSi - FPD

Delft Thorascan

aSe - Slot Scan CCD

GE Revolution XQ/i

aSi - FPD

Delft Thorascan

aSe - Slot Scan CCD

Influence of scatter on image quality. The leftmost image of each pair represents an image acquired on a full-field digital chest radiography system (120 kVp, 0.02 mSv) while the rightmost image of each pair was acquired using a slot-scan detector (140 kVp, 0.02 mSv).  The improved contrast obtained with the slot-scan detector, relative to that obtained with an aSi full field flat panel detector employing a conventional antiscatter grid, contradicts the results of conventional DQE measurements which predict that for comparable entrance exposures, the full field digital chest radiography system should outperform the slot-scan system.


An example of our contributions to the advancement of digital radiography imaging metrology is our newly introduced performance metric, effective detective quantum efficiency (eDQE). Unlike conventional DQE evaluations which are performed under ideal conditions to capture the intrinsic performance of the detection system independent of application, eDQE evaluations are intended to reflect clinical conditions which include the effects of magnification, focal spot blurring, scatter from the patient, and effects of the anti-scatter device. Our work validating this new metric was focused on the digital chest radiography application where we established that, in comparison to the eDQE, the conventional metric, DQE, fell short of reflecting the system performance under typical clinical conditions revealing its limitations in predicting the relative performance of these systems in the clinic. More recent work is focused on the application of the eDQE methodology to mammography.


Conventional DQE

 

Effective DQE (eDQE)

 
Compliments of A. Mackenzie, K-Care
 

 

 


Comparing the computation of DQE and eDQE metrics.

 


In addition to our ongoing research in image quality metrology, various members of RAI Labs serve in leadership roles within the AAPM to improve image quality metrology and assessment. The AAPM Task Group 162, chaired by Ehsan Samei, is developing a suite of software tools for evaluating the MTF, NPS and DQE/eDQE of radiographic systems. Prototype software has been developed within RAI Labs and beta testing is currently underway. The AAPM Task Group 150, with co-chair Nicole Ranger and member Ehsan Samei, is developing guidelines and recommendations for acceptance testing of digital radiography imaging systems. The AAPM Task Group 171, with Ehsan Samei, Joseph Lo and James Dobbins as members, is developing guidelines for acceptance testing of digital tomosynthesis systems.


References

  • Samei E, Saunders RS, Lo JY, Dobbins III JT, Jesneck JL, Floyd CE, Ravin CE. Fundamental imaging characteristics of a slot-scan digital chest radiographic system. Med Phys 2004; 31:2687-2698.
  • Samei E, Ranger NT, Dobbins III JT, 3rd, Chen Y. Intercomparison of methods for image quality characterization. I. Modulation transfer function. Med Phys 2006; 33:1454-1465.
  • Dobbins III JT, Samei E, Ranger NT, Chen Y. Intercomparison of methods for image quality characterization. II. Noise power spectrum. Med Phys 2006; 33:1466-1475.
  • Ranger NT, Samei E, Dobbins III JT, Ravin CE. Assessment of detective quantum efficiency: intercomparison of a recently introduced international standard with prior methods. Radiology 2007; 243:785-795.
  • Samei E, Ranger NT, MacKenzie A, Honey ID, Dobbins JTD III, Ravin CE. Detector or System ? Extending the concept of detective quantum efficiency to characterize the performance of digital radiographic imaging systems. Radiology 2008; 249:926-937.
  • Ranger NT, Mackenzie A, Honey ID, Dobbins JT III, Ravin CE, Samei E. Extension of DQE to include scatter, grid, magnification, and focal spot blur: A new experimental technique and metric. Proc. SPIE 7258: 72581A (2009).
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