Dual Energy

It allows the separation of soft tissue from bones in chest X-ray images obtained by double exposure

The Dual Energy is an advanced radiographic application that can improve the efficiency and the diagnostic results by eliminating anatomical structures that could otherwise hide pathologies.

The Dual Energy acquisition allows the separation of soft tissue from hard tissue by image subtraction, thus obtaining two distinct images, one for each component. This technique takes advantage of the differences in the attenuation of low and high energy of the respective tissues. Double-exposure Dual Energy is based on two consecutive ray emissions at different kVp, with a single detector.

The result of the acquired images strongly depends on the energy and on the time elapsing between the two exposures. The energy values used are normally in the range of 60-90 kVp for the low-energy exposure and 120-150 kVp for the high-energy one, while the time between the two exposures must be limited to its maximum in order to reduce the artifacts due to the patient’s movement.

It is mainly used in chest radiographies because they are the most difficult to interpret. As a matter of fact, the dense structure of the ribs which includes and covers the underlying complex anatomy of the lungs and the heart are located in the chest.

By managing to provide two separate images of bone tissue and soft tissue, the Dual Energy is a valid diagnosis support for radiologists, as it improves the visualization of the patient’s anatomy.

Clinical advantages:

Several studies are reported in scientific literature on the diagnostic benefits of the acquisition by the Dual Energy technique, in particular for thorax radiography. For example, the detection sensitivity of lung anomalies is improved, because the characteristics that are often difficult to visualize in standard chest radiographies become more evident when the above rib superstructures are removed.

Besides, the Dual Energy allows a quantification grade for some material characteristics that can help to improve specificity. For example, calcified lung nodules appear more evident in bone-only images, which is usually an indication of the fact that the lesion is benign.

Other published scientific articles have reported that soft tissue images provide an overall bigger sensitivity for the detection of infectious consolidations, interstitial lung alterations and aortic or tracheal calcifications.

The Dual Energy allows a better visualization of a variety of entities, including nodules, bone lesions, vascular pathologies, pleural pathologies, mediastinal and hilar masses, tracheal and airway anomalies, complex thoracic pathologies and indwelling devices.

The Dual Energy removes the above bone structures in order to create selective images of the soft tissues. The above bone structures may hide lung nodules, therefore the selective images of the soft tissues allow viewing the structures of the latter more clearly, including nodules that are located at the basis of the bone. Besides, it generates selective images for the bone that allow the detection of calcium, thus improving the ability to detect calcified and non-calcified nodules.

Bone lesions
The Dual Energy improves the detection and the characterization of bone lesions. The selective images of the bone make bone lesions more evident than in conventional radiographies. These pathologies include bone metastasis, primary bone cancers (both benign and malignant), rib fractures, rib erosions and post-surgical modifications.

Vascular pathologies
The selective images of the bone highlight vascular calcifications and help to detect pathologies of the arteries and the great blood vessels. The Dual Energy also improves the visualization of heart calcifications, including valve, pericardial and myocardial calcifications.

Pleural pathologies
Thanks to the Dual Energy, a radiologist can identify pleural calcifications and pleural plaques calcifications with greater certainty.

Mediastinal and hilar masses
The selective images of the soft tissues help to detect the dimensions, the shape and the opacity changes of the hilum and improve the ability to identify mediastinal and hilar pathologies.

Tracheal and airway anomalies
Tracheal anomalies can be more easily detected on images obtained by Dual Energy, that can remove the thoracic spinal column which is above and hides the thorax airways. The selective images of the soft tissues show more immediately tracheal stenosis and trachea shrinking due to the extrinsic compression by adjacent masses or adenopathy.

Complex thoracic pathologies
The removal of bone structures allows the detection of lesions in areas that are difficult to see (for example the apices, behind the heart and under the clavicles and the ribs). The Dual Energy also makes the most subtle changes in the context of complex multifocal pathologies evident. Besides, temporal subtraction techniques may be used to discern subtle changes from one test to the other.

Indwelling devices
The Dual Energy improves the visualization of foreign bodies. Indwelling devices can be seen more easily on the selective images of the bone, these entities include mammary prostheses, surgical clips, catheters and catheter fragments and vascular stents (including coronary artery stents).

Synchronization with pulse oximeter:

Yet, despite its many advantages, the Dual Energy technique also has some limitations. The main one is related to the 200-millisecond delay occurring between the two exposures. This delay may cause artifacts on the removed images due to slight offsets in the alignment of the body structures caused by diverse types of patient’s movements (such as the heartbeat).

The artifacts are seen as white or black lines on one or both the subtracted images (normally more evident on the image that emphasizes the bone component).

Among the most common artifacts, there is the one due to the heart movement. In order to eliminate such artifact, it is possible to synchronize the acquisition of the two images by means of a pulse oximeter.

The system will be able to synchronize the RX exposure signals with the heartbeat.

The exposures occur during the diastolic phase of the heart cycle with atriums and ventricles as relaxed as possible. The two exposures can be performed in diastolic phases of subsequent heart cycles or during the diastolic phase of a single heart cycle.

This functionality will be included in futurre release of Digitec software.

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