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From anwar scans

Reference: Mark Woods, Marcus Brehm

siemens-healthineers.com/tin-filter.

How can the Siemens Healthineers CT Scanner help to reduce radiation to  ultra-low dose while retaining high-definition image quality?

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Tube in the CT machine emits X-ray beam with a certain spectrum which  includes photons over a wide energy range. Photons with low energy range do not contribute to the measured signal and are therefore useless for imaging but still contribute to patient radiation dose and cause artifacts.

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The Tin Filter used in Siemens CT cuts out lower energies from the emitting beam and thereby  reduces the dose and improves image quality.

Furthermore, beam-hardening artifacts are significantly reduced by spectral shaping in Siemens that uses a bow tie special filter.

This basic but powerful filtration is complemented further by what is termed the Adaptive Dose Shield an additional movable collimators that stop the X-ray beam completely and allow for dynamic collimation. These are used clinically to stop over-beaming of helical scans so that extra dose is not to the patient when it will not enable image creation.

Depending on the patient size or region of interest, a movable beam-shaping filter that differs in shape may be used instead of or in addition to the default filter. This is very much useful in paediatric imaging.

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Lung with Tin Filter :According to Gordic et al., the patient images acquired at Sn100 kV were of diagnostic quality both at 1/10th of the standard dose (corresponding to an effective patient dose of about 0.13 mSv) and at 1/20th of the standard dose (corresponding to an effective patient dose of about 0.06–0.07 mSv).Note that this is the dose level of a chest X-ray examination.

 

Urinary Stones with Tin Filter: Utilizing CT for detection of urinary stones instead of X ray is  hampered by the question of dose in CT. Here spectral shaping with Tin Filter can help, with one publication assessing radiation dose during urinary stone detection in unenhanced CT. The authors compared tin-filtered 150 kV (Sn150 kV) and automated kV selection (110–140 kV) based on the scout view on the same CT-device. The authors found more than a 30 percent decrease in the CTDIvol with Tin Filter spectral shaping, while at the same time, they saw an improved image quality.An additional study also concluded that using spectral shaping with tin filtration can substantially reduce radiation dose compared with routine abdominal CT for urinary stone disease

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Paranasal Sinuses with Tin Filter :A prospective study on CT imaging of the paranasal sinuses compared a protocol at 150 mAs, 100 kV and tin filtration (Sn100 kV) to a low-dose protocol at 50 mAs and 100 kV.The results showed a statistically significantly lower CTDIvol in the study group (1.2 mGy vs. 4.4 mGy, p < 0.001) With Tin Filter, non-contrast Sinus CT can be performed on patients at

X-ray dose levels, in one easy position.

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 Spine imaging with Tin Filter :Clinical evaluation of cervical, thoracic and lumbro-sacral spine regions is common when searching for underlying acute or chronic fractures or structural anatomical variants, be it in trauma or even oncological settings. One study to investigate the image quality, radiation dose of cervical spine CT using spectral shaping at 140 kV with a Tin Filter (Sn140 kV) in comparison with conventional CT at 120 kV.Here it was concluded that cervical spine CT using Sn140 kV improves image quality of the lower cervical region without increasing the radiation dose. Thus, this protocol can be helpful to overcome the artifacts in CT images of the lower cervical spine.

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Whole Body CT with Tin Filter :Studies to investigate the radiation dose and image quality of a whole-body low-dose CT using spectral shaping at 100 kV (Sn100 kV) for the assessment of osteolytic lesions in patients with multiple myeloma were performed and concluded that the scans performed with spectral shaping can obtain sufficient image quality to depict osteolytic lesions while reducing radiation dose by approximately 74%. Full-body, skeletal survey can be performed in one simple low-dose CT scan.  CT colonography as a non-invasive procedure to detect polyps has been performed for many years, however with the addition of the Tin Filter, it is possible to detect polypoid lesions with very low dose radiation settings.Additionally, retrospective studies comparing standard dose protocols versus Tin Filter-based protocols concluded that the Tin Filter enables consistent sub-mSv colonography without substantially impairing image quality.

Extremities with Tin Filter :Orthopaedic examinations have generally been the realm of plain film radiography, however now with spectral shaping and the Tin Filter, it may be possible to move towards a CT scan for these procedures. This would provide high quality 3D data of CT, with a clear reduction of 2D projection errors (overshadowing or positional), at the same dose as the plain X-ray series.

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Topogram with Tin Filter :Given the significantly reduced dose of CT, especially with implementation of low-kV imaging and tin-filtered imaging, the dose of the routine topogram or planning scan may make up a significant portion of the overall CT dose. Therefore, it is also possible to implement the Tin Filter for the topogram scan, enabling a significant dose reduction while also maintaining the dose selection parameters of a routine kV topogram.

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Intervention with Tin Filter :Invasive interventional procedures in CT are becoming more commonplace. Scanning of the patient to monitor the needle position is important in these cases, however there may be the potential for increased dose when the procedure or patients anatomy is complex. Utilizing the Tin Filter, the overall dose of interventional procedures may be reduced, because each individual scan uses the dose reduction potential.

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Angiography with Tin Filters :

Radiologists are relying on the rich diagnostic possibilities offered by high quality images of angiography.

The technology improves iodine enhancement and helps to compare and quantify lesions and tissues, or to reduce metal artifacts.

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Orthopaedic imaging of acute bone injury : High spatial resolution  CT images can give fine structural details . High resolution 3D reconstruction can give best information to the treating  orthopedicians

In particular, the full potential of spectral shaping is still unknown and awaits stronger external clinical proof beyond the testing performed by Siemens Healthineers. Low-dose brain imaging and low-dose facial bone imaging in trauma are just two examples.

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Conclusion

The advancement in additional spectral shaping techniques, such as Tin Filter  shift the conversation from mere routine imaging to  the potential of plain X-ray dose levels for CT scans.