Tuesday 16 December 2014

X-ray computed tomography (CT scans)


All of our survey equipment and samples arrived in Belgium safely. Time to get the real work started! 

Before opening the cores from Lake Hamana, three-dimensional tomographic images were made with a medical CT scanner at the Ghent University Hospital (UZ Ghent). Indeed, the same device doctors use to look at bone fractures or detect other medical conditions. The X-ray CT technology is based on sending out a fan-shaped beam of computer processed X-rays from a helically revolving source. These rays become attenuated by a centrally positioned sample object (in this case, a sediment core) and collected again by a rotating array of detector cells. This setup allows to make full body scans of the objects of interest (Last & Smol, 2001). Resulting 3D images are a composite of series of 2D tomographic slices, in which every volume element (voxel) is represented by a specific shade of grey. These greyscales are a reflection of the measure in which the X-ray beam has been attenuated along its pathway and depend on the density as well as the composition of the sediment (Orsi et al., 1994). White voxels correspond to a complete attenuation of the signal, whereas black ones indicate no attenuation at all. Generally coarser grained sediment tends to attenuate the signal more severely than finer grained material. Also, every mineral generates its own characteristic attenuation, which is a function of the applied level of radiation energy.

Schematic side view and cross view of a medical CT scanner while imaging a sediment core. A rotating X-ray source continuously sends out a fan-shaped beam, which is received again by the synchronously revolving detector array. Meanwhile a motorised table gradually moves the core through the scanner, resulting in a helical scanning path. 

Within the QRN-project, CT images will be used mainly to identify depositional structures that are impossible or difficult to recognise on split surface photographs. They allow us to obtain a first impression of the content of the cores before even opening them. Moreover, processing software makes it possible to manipulate the data in order to enhance the visibility of specific features (e.g. coarse grained intercalations (tsunami deposits?), shells, rocks, laminations, cross stratification…).

Top: CT scanner at the Ghent University Hospital, illustrating the setup for X-ray core scanning on an already opened liner (not from Lake Hamana). Bottom: Example (core from Lake Kenai, Kenai Peninsula, south-central Alaska) of how resulting CT images (A) tend to look like, compared to original sediment surface pictures (B). This record is composed of an earthquake triggered event deposit or ‘turbidite’ (brown line) embedded within background laminations (light blue lines).

Timelapse of the Ghent University Hospital X-ray CT scanner in action. 


References

Last, W.M. and Smoll, J.P. (2001). Tracking environmental change using lake sediments. Volume 2: Physical and geochemical methods. Kluwer Academic Publishers. 515 pp.

Orsi, T.H., Edwards, C.M. and Anderson, A.L. (1994). X-ray computed tomography: A non-destructive method for quantitative analysis of sediment cores. Journal of Sedimentary Research 64A, 690-693.      

12 comments:

  1. Hello I am really impressed with this blog! Very clear explanation of issues is given and it is open to everyone. Thanks for sharing this post. When i was also searching for CT Scan Centre in Jayanagar, Bangalore. I got one new center that is Prima Diagnostics. It is excellent centre for CT Scan Centre in Jayanagar, Bangalore. If you are also searching for best diagnostics centre you can visit here. If you want any more info. please go here http://www.primadiagnostics.com/

    ReplyDelete
  2. City x-ray and Scan Clinic (P) Ltd is one of the best diagnostic centers in Delhi, which offers best CT scan, 3T MRI, Ultrasound, CT Angiography, Radiology facilities. You can book a test and get the reports online.

    ReplyDelete
  3. It is useful particularly for these types of organs in the body. Though we know that other medical techniques which involve the imaging processes like MRI, X-ray or CT scan are all old techniques that uses ionizing radiation technique.

    ReplyDelete
  4. https://clermontradiology.blogspot.com/2016/05/what-happens-inside-mri-machine-during.html?showComment=1607745463755#c3938836984157278670

    ReplyDelete
  5. Nice blog post. The information which you shared about the topic is exactly right. I keep visiting your blog. National MRI Scan makes healing simpler by providing the facility of Private MRI Scan in Newark, UK.

    ReplyDelete
  6. I’m shocked read your article on your blogger amazing information get to usefully knowable tips. Like At Medimages, we design and develop advanced medical imaging software solutions. PACS Software, DICOM Software.

    ReplyDelete
  7. Your computed tomography content is really extraordinary... i'm really happy that you have mentioned about x ray as well... radolabs Scan Centre Chennai operates the same way

    ReplyDelete