SUSPENSION CRITERIA FOR IMAGE MONITORS AND VIEWING BOXES.

Image monitors and viewing boxes have a crucial role in the diagnostic process. Modern radiology uses different modalities to produce digital images which are to be viewed in different parts of the radiology department and throughout the hospital, sometimes simultaneously, via the Picture Archiving and Communications System (PACS). Therefore, the quality of the image monitors is of great importance. IPEM notes that inadequacies in the imaging viewing area may serve to negate the benefits of other efforts made to maintain quality and consistency. Suspension criteria for diagnostic image monitors and viewing boxes are presented in RP162. These criteria are mainly based on two documents, IPEM report 91, 'Recommended standards for the routine performance testing of diagnostic x-ray imaging systems' (2005) and AAPM on-line report no. 03, 'Assessment of display performance for medical imaging systems' (2005). The development of common European suspension levels for image monitors and viewing boxes will be a valuable tool in quality assurance

How does image quality affect radiologists' perceived ability for image interpretation and lesion detection in digital mammography?

OBJECTIVES: To study how radiologists' perceived ability to interpret digital mammography (DM) images is affected by decreases in image quality. METHODS: One view from 45 DM cases (including 30 cancers) was degraded to six levels each of two acquisition-related issues (lower spatial resolution and increased quantum noise) and three post-processing-related issues (lower and higher contrast and increased correlated noise) seen during clinical evaluation of DM systems. The images were shown to fifteen breast screening radiologists from five countries. Aware of lesion location, the radiologists selected the most-degraded mammogram (indexed from 1 (reference) to 7 (most degraded)) they still felt was acceptable for interpretation. The median selected index, per degradation type, was calculated separately for calcification and soft tissue (including normal) cases. Using the two-sided, non-parametric Mann-Whitney test, the median indices for each case and degradation type were compared. RESULTS: Radiologists were not tolerant to increases (medians: 1.5 (calcifications) and 2 (soft tissue)) or decreases (median: 2, for both types) in contrast, but were more tolerant to correlated noise (median: 3, for both types). Increases in quantum noise were tolerated more for calcifications than for soft tissue cases (medians: 3 vs. 4, p = 0.02). Spatial resolution losses were considered less acceptable for calcification detection than for soft tissue cases (medians: 3.5 vs. 5, p = 0.001). CONCLUSIONS: Perceived ability of radiologists for image interpretation in DM was affected not only by image acquisition-related issues but also by image post-processing issues, and some of those issues affected calcification cases more than soft tissue cases. KEY POINTS: • Lower spatial resolution and increased quantum noise affected the radiologists' perceived ability to interpret calcification cases more than soft tissue lesion or normal cases. • Post-acquisition image processing-related effects, not only image acquisition-related effects, also impact the perceived ability of radiologists to interpret images and detect lesions. • In addition to current practices, post-acquisition image processing-related effects need to also be considered during the testing and evaluation of digital mammography systems

X-RAY TOMOSYNTHESIS: A REVIEW OF ITS USE FOR BREAST AND CHEST IMAGING.

Tomosynthesis is a three-dimensional imaging technique based on the reconstruction of several planar radiographs. During the image acquisition in tomosynthesis, the X-ray tube moves around the detector which is often stationary, and a number of projection images are taken from different angles. Individual slices from the reconstructed volume can be studied. With the effective reduction of the visibility of the overlapping normal tissue, the detection of pathological lesions is improved when compared with projection radiography. Up to now, tomosynthesis has mainly been used for breast and chest examinations and, to some extent, also for orthopaedic, angiographic and dental investigations. For chest, tomosynthesis is used as an alternative to computed tomography with significantly lower cost and radiation dose to the patient. Breast tomosynthesis has, in several studies, proved to be an effective tool for improving detection of breast lesions. As tomosynthesis has many properties that make it suitable as a modality for screening, including good diagnostic performance, short examination time and low radiation dose, it is a strong competitor to the current gold standard breast screening modality, i.e. mammography. In this paper, the principles of tomosynthesis will be presented as well as a few clinical studies showing the potential role of tomosynthesis in clinical routine examinations

Quantifying the quality of medical x-ray images. An evaluation based on normal anatomy for lumbar spine and chest radiography.

Optimisation in diagnostic radiology requires accurate methods for determination of patient absorbed dose and clinical image quality. Simple methods for evaluation of clinical image quality are at present scarce and this project aims at developing such methods. Two methods are used and further developed; fulfilment of image criteria (IC) and visual grading analysis (VGA). Clinical image quality descriptors are defined based on these two methods: image criteria score (ICS) and visual grading analysis score (VGAS), respectively. For both methods the basis is the Image Criteria of the “European Guidelines on Quality Criteria for Diagnostic Radiographic Images”. Both methods have proved to be useful for evaluation of clinical image quality. The two methods complement each other: IC is an absolute method, which means that the quality of images of different patients and produced with different radiographic tech-niques can be compared with each other. The separating power of IC is, however, weaker than that of VGA. VGA is the best method for comparing images produced with different radiographic techniques and has strong separating power, but the re-sults are relative, since the quality of an image is compared to the quality of a refer-ence image. The usefulness of the two methods has been verified by comparing the results from both of them with results from a generally accepted method for evaluation of clinical image quality, receiver operating characteristics (ROC). The results of the comparison between the two methods based on visibility of anatomical structures and the method based on detection of pathological structures (free-response forced error) indicate that the former two methods can be used for evaluation of clinical image quality as efficiently as the method based on ROC. More studies are, however, needed for us to be able to draw a general conclusion, including studies of other organs, using other radiographic techniques, etc. The results of the experimental evaluation of clinical image quality are compared with physical quantities calculated with a theoretical model based on a voxel phantom, and correlations are found. The results demonstrate that the computer model can be a useful tool in planning further experimental studies

Search for optimal tube voltage for image plate radiography

Purpose: To search for the tube voltage which results in the highest clinical image quality per effective dose unit for chest and pelvis radiography respectively, using image plates. Methods: Two anthropomorphic phantoms were imaged with several different tube voltages. For the chest phantom, the tube voltage was varied between 70 and 150 kV, and for the pelvis phantom between 50 and 102 kV. The mAs settings were chosen so that the effective dose to the phantom was the same, regardless of the tube voltage, for the two examinations respectively. The clinical image quality of the resulting images was evaluated by a panel of experienced radiologists with visual grading analysis of defined anatomical structures taken from the European Image Criteria. Images produced with the standard tube voltage settings (125 kV for chest and 70 kV for pelvis) were used as reference. These two kV settings were previously used for screen film radiography. Results: For both the chest and the pelvis examinations the image quality at a constant level of effective dose increased when the tube voltage was reduced. Conclusions: The image quality of image plate radiography can be increased by lowering the tube voltage compared to what was used for screen film radiography

Dose-length-product determination on cone beam computed tomography through experimental measurements and dose-area-product conversion

The dosimetry of cone beam computed tomography (CBCT) is not fully elaborated yet, and some of these systems presents dose-area-product (DAP) values after an examination rather than, as in the case of traditional CT, the doselength- product (DLP). The purpose of this study was to provide a reproducible and straight-forward method for DLP measurements on CBCT, as well as to validate a tool for estimating DLP for a CBCT system in terms of accuracy. A prototype conversion tool for estimating DLP, using the DAP value, was provided by the vendor of a CBCT system which currently display only DAP. The DAP to DLP conversion tool was validated using five protocols for extremity imaging. DLP was measured using a 30 cm ionization chamber and 30 cm long cylindrical PMMA-phantom. DLP, the integrated absorbed dose within the ionization chamber, was measured through central and peripheral measurements in the phantom in order to calculate the weighted DLP, DLPW,CBCT. Comparisons between DLPW,CBCT and estimated DLP, showed that the conversion tool was accurate within 10%, with a mean average error of 6.1% for all measured protocols. The variation between repeated measurements was small, making the method highly reproducible. In conclusion, in this study a simple method for determining DLP on CBCT was presented, and it was validated that the conversion tool can present the delivered dose in terms of DLP with high accuracy. The measured DLP, as well as the DLP estimated by the conversion tool, is suitable for quality control and relative dose comparisons between protocols, but its’ relation to the DLP of CT systems should be investigated further in order to relate to patient dose

Digital mammography and tomosynthesis for breast cancer diagnosis

Introduction: Mammography is one of the most common X-ray examinations although it is well-known that the anatomical background of the breast is the main obstacle when it comes to detection of breast lesions with this method. Tomosynthesis is a three-dimensional radiographic technique which, to a large extent, can suppress the confounding effect of the anatomical background. Tomosynthesis is a strong competitor to mammography both for screening and clinical examinations. Areas covered: This paper gives a description of digital mammography (DM) and breast tomosynthesis (BT). Relevant studies exploring the possibilities of BT from a technical and clinical point of view, in comparison with DM, are presented. The reader will learn about the concept of BT as well as its advantages compared with DM. The review highlights both diagnostic and clinical aspects of BT as well as the challenges that remain before BT can be fully incorporated in clinical breast cancer imaging and potentially in screening. Expert opinion: BT has the potential to considerably improve breast cancer diagnostics and offers advantages to the existing techniques. It has applications both for clinical breast cancer imaging as well as for screening purposes. The true potential of BT in both fields remains to be further evaluated in clinical trials