4DCT

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Spiral 4DCT Lung (Post).gif Spiral 4DCT Lung (Lateral).gif
Lung motion in 4DCT

Four-dimensional computed tomography (4DCT) is a type of CT scanning which records multiple images over time. It allows playback of the scan as a video, so that physiological processes can be observed and internal movement can be tracked. The name is derived from the addition of time (as the fourth dimension) to traditional 3D computed tomography. Alternatively, the phase of a particular process, such as respiration, may be considered the fourth dimension. [1]

Contents

Fluoroscopy is a similar technique to 4DCT, however it refers to the introduction of a time element to 2D planar radiography, rather than to 3D CT. [2] [3] [4] [5]

Applications

Radiotherapy

4DCT is used in radiation therapy planning to reduce doses to healthy organs such as the heart or lungs. Most radiation therapy is planned using the results of a 3D CT scan. A 3D scan largely presents a snapshot of the body at a particular point in time, however due to the time of the acquisition, in which the patient is likely to have moved in some way (even if only breathing), there will be an element of blurring or averaging in the 3D scan. [6] When it comes to treatment planning, this motion can mean there is less accuracy in the positioning of treatment beams, and reduce the likelihood of a repeatable set-up on the linear accelerator when it comes to treatment. [7]

To minimise physical movements of the patient, some sort of immobilisation is typically used. To overcome physiological motion, such as breathing, 4DCT acquires images at a range of times and positions, allowing the extent of motion to be visualised (e.g. from maximum inspiration to maximum exhalation). The treatment plan can then be designed with a knowledge of the full range of possible positions of important organs, and the tumour (target) itself. [8]

4DCT will usually involve a gating technique, such as breathing tracking, so that image acquisition is automatically triggered at set points. [9] This gating can also be applied at treatment, where the radiotherapy beam is only switched on at certain points in the breathing cycle (as in the deep inspiration breath-hold technique). [10]

Diagnostic radiology

4DCT has started to be used for diagnostic radiology procedures, for example looking at joint problems, the cardiac cycle and parathyroid washout of contrast. Downsides of 4DCT for diagnostic purposes include large and complex datasets, and increased radiation dose to the patient. [11]

Reconstruction methods

4DCT aims to visualise the temporal dynamics of a 3D sample with a sufficiently high temporal and spatial resolution. Successive time frames are typically obtained by sequential scanning, followed by independent reconstruction of each 3D dataset. Such an approach requires a large number of projections for each scan to obtain images with sufficient quality (in terms of artefacts and SNR). Hence, there is a clear trade-off between the rotation speed of the gantry (i.e. time resolution) and the quality of the reconstructed images. Motion vector based Iterative Techniques are available which reconstruct a particular time frame by including the projections of neighbouring time frames as well. Such a strategy allows to improve the trade-off between the rotation speed and the SNR. [12]

For fluid dynamics, specialized reconstruction algorithms have been developed that model the attenuation course throughout time. [13] An example of such fluid dynamics is perfusion CT in which the propagation of contrast agent is modelled and simultaneously estimated with the CT images. [14]

Related Research Articles

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Positron emission tomography Medical imaging technique

Positron emission tomography (PET) is a functional imaging technique that uses radioactive substances known as radiotracers to visualize and measure changes in metabolic processes, and in other physiological activities including blood flow, regional chemical composition, and absorption. Different tracers are used for various imaging purposes, depending on the target process within the body. For example, 18
F
-FDG is commonly used to detect cancer, NaF18
F
 is widely used for detecting bone formation, and oxygen-15 is sometimes used to measure blood flow.

Radiation therapy Therapy using ionizing radiation, usually to treat cancer

Radiation therapy or radiotherapy, often abbreviated RT, RTx, or XRT, is a therapy using ionizing radiation, generally provided as part of cancer treatment to control or kill malignant cells and normally delivered by a linear accelerator. Radiation therapy may be curative in a number of types of cancer if they are localized to one area of the body. It may also be used as part of adjuvant therapy, to prevent tumor recurrence after surgery to remove a primary malignant tumor. Radiation therapy is synergistic with chemotherapy, and has been used before, during, and after chemotherapy in susceptible cancers. The subspecialty of oncology concerned with radiotherapy is called radiation oncology. A physician who practices in this subspecialty is a radiation oncologist.

CT scan Medical imaging procedure using X-rays to produce cross-sectional images

A computed tomography scan is a medical medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers or radiology technologists.

External beam radiotherapy Treatment of cancer with ionized radiation

External beam radiotherapy (EBRT) is the most common form of radiotherapy. The patient sits or lies on a couch and an external source of ionizing radiation is pointed at a particular part of the body. In contrast to brachytherapy and unsealed source radiotherapy, in which the radiation source is inside the body, external beam radiotherapy directs the radiation at the tumour from outside the body. Orthovoltage ("superficial") X-rays are used for treating skin cancer and superficial structures. Megavoltage X-rays are used to treat deep-seated tumours, whereas megavoltage electron beams are typically used to treat superficial lesions extending to a depth of approximately 5 cm. X-rays and electron beams are by far the most widely used sources for external beam radiotherapy. A small number of centers operate experimental and pilot programs employing beams of heavier particles, particularly protons, owing to the rapid dropoff in absorbed dose beneath the depth of the target.

Brachytherapy Type of radiation therapy

Brachytherapy is a form of radiation therapy where a sealed radiation source is placed inside or next to the area requiring treatment. Brachy is Greek for short. Brachytherapy is commonly used as an effective treatment for cervical, prostate, breast, esophageal and skin cancer and can also be used to treat tumours in many other body sites. Treatment results have demonstrated that the cancer-cure rates of brachytherapy are either comparable to surgery and external beam radiotherapy (EBRT) or are improved when used in combination with these techniques. Brachytherapy can be used alone or in combination with other therapies such as surgery, EBRT and chemotherapy.

Nuclear medicine Medical specialty

Nuclear medicine, is a medical specialty involving the application of radioactive substances in the diagnosis and treatment of disease. Nuclear imaging, in a sense, is "radiology done inside out" because it records radiation emitting from within the body rather than radiation that is generated by external sources like X-rays. In addition, nuclear medicine scans differ from radiology, as the emphasis is not on imaging anatomy, but on the function. For such reason, it is called a physiological imaging modality. Single photon emission computed tomography (SPECT) and positron emission tomography (PET) scans are the two most common imaging modalities in nuclear medicine.

Proton therapy Medical Procedure

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Radiation treatment planning

In radiotherapy, radiation treatment planning (RTP) is the process in which a team consisting of radiation oncologists, radiation therapist, medical physicists and medical dosimetrists plan the appropriate external beam radiotherapy or internal brachytherapy treatment technique for a patient with cancer.

Tomotherapy

Tomotherapy is a radiation therapy modality, in which the patient is scanned across a modulated strip-beam, so that only one “slice” of the target is exposed at any one time by the linear accelerator (linac) beam. The three components distinctive to this modality are: (1) a collimator pair that defines the length of the strip, (2) a binary multileaf collimator whose leaves open and close during treatment to modulate the strip’s intensity, and (3) a couch that scans the patient across the beam at a fixed speed during the treatment delivery.

CT pulmonary angiogram

A CT pulmonary angiogram (CTPA) is a medical diagnostic test that employs computed tomography (CT) angiography to obtain an image of the pulmonary arteries. Its main use is to diagnose pulmonary embolism (PE). It is a preferred choice of imaging in the diagnosis of PE due to its minimally invasive nature for the patient, whose only requirement for the scan is an intravenous line.

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PET-CT

Positron emission tomography–computed tomography is a nuclear medicine technique which combines, in a single gantry, a positron emission tomography (PET) scanner and an x-ray computed tomography (CT) scanner, to acquire sequential images from both devices in the same session, which are combined into a single superposed (co-registered) image. Thus, functional imaging obtained by PET, which depicts the spatial distribution of metabolic or biochemical activity in the body can be more precisely aligned or correlated with anatomic imaging obtained by CT scanning. Two- and three-dimensional image reconstruction may be rendered as a function of a common software and control system.

A dose-volume histogram (DVH) is a histogram relating radiation dose to tissue volume in radiation therapy planning. DVHs are most commonly used as a plan evaluation tool and to compare doses from different plans or to structures. DVHs were introduced by Michael Goitein and Verhey in 1979. DVH summarizes 3D dose distributions in a graphical 2D format. In modern radiation therapy, 3D dose distributions are typically created in a computerized treatment planning system (TPS) based on a 3D reconstruction of a CT scan. The "volume" referred to in DVH analysis is a target of radiation treatment, a healthy organ nearby a target, or an arbitrary structure.

PET-MRI

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Cone beam computed tomography

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References

  1. ↑ Cox, James D.; Chang, Joe Y.; Komaki, Ritsuko (2007). Image-Guided Radiotherapy of Lung Cancer. CRC Press. p. 85. ISBN   9780849387821.
  2. ↑ Menze, Bjoern; Langs, Georg; Tu, Zhuowen; Criminisi, Antonio (2011). Medical Computer Vision: Recognition Techniques and Applications in Medical Imaging. Springer. p. 63. ISBN   9783642184215.
  3. ↑ Jr, Brendan C. Stack; Bodenner, Donald L. (2016). Medical and Surgical Treatment of Parathyroid Diseases: An Evidence-Based Approach. Springer. p. 152. ISBN   9783319267944.
  4. ↑ Chin, Lawrence S.; Regine, William F. (2015). Principles and Practice of Stereotactic Radiosurgery. Springer. p. 191. ISBN   9781461483632. The ITV can be assessed with a 4D CT scan or fluoroscopy...
  5. ↑ Jeremic, Branislav (2011). Advances in Radiation Oncology in Lung Cancer. Springer Science & Business Media. p. 160. ISBN   9783642199257.
  6. ↑ Korreman, Stine S (7 December 2012). "Motion in radiotherapy: photon therapy". Physics in Medicine and Biology. 57 (23): R161–R191. Bibcode:2012PMB....57R.161K. doi: 10.1088/0031-9155/57/23/R161 . PMID   23165229.
  7. ↑ De Ruysscher, Dirk; Faivre-Finn, Corinne; Nestle, Ursula; Hurkmans, Coen W.; Le Péchoux, Cécile; Price, Allan; Senan, Suresh (20 December 2010). "European Organisation for Research and Treatment of Cancer Recommendations for Planning and Delivery of High-Dose, High-Precision Radiotherapy for Lung Cancer". Journal of Clinical Oncology. 28 (36): 5301–5310. doi: 10.1200/JCO.2010.30.3271 . PMID   21079134.
  8. ↑ Schlegel, Wolfgang C.; Bortfeld, Thomas; Grosu, Anca Ligia (2006). New Technologies in Radiation Oncology. Springer Science & Business Media. p. 83. ISBN   9783540299998.
  9. ↑ Maciejczyk, Adam; Skrzypczyńska, Iga; Janiszewska, Marzena (November 2014). "Lung cancer. Radiotherapy in lung cancer: Actual methods and future trends". Reports of Practical Oncology & Radiotherapy. 19 (6): 353–360. doi:10.1016/j.rpor.2014.04.012. PMC   4201776 . PMID   25337407.
  10. ↑ Glide-Hurst, Carri K.; Chetty, Indrin J. (2014). "Improving radiotherapy planning, delivery accuracy, and normal tissue sparing using cutting edge technologies". Journal of Thoracic Disease. 6 (4): 303–318. doi:10.3978/j.issn.2072-1439.2013.11.10. ISSN   2072-1439. PMC   3968554 . PMID   24688775.
  11. ↑ Kwong, Yune; Mel, Alexandra Olimpia; Wheeler, Greg; Troupis, John M (October 2015). "Four-dimensional computed tomography (4DCT): A review of the current status and applications". Journal of Medical Imaging and Radiation Oncology. 59 (5): 545–554. doi:10.1111/1754-9485.12326. PMID   26041442. S2CID   25440312.
  12. ↑ Van Nieuwenhove, Vincent; De Beenhouwer, Jan; Vlassenbroeck, Jelle; Brennon, Mark; Sijbers, Jan (2017). "MoVIT: A tomographic reconstruction framework for 4DCT". Optics Express. 25 (16): 19236–19250. Bibcode:2017OExpr..2519236V. doi: 10.1364/OE.25.019236 . PMID   29041117.
  13. ↑ Van Eyndhoven, Geert; Batenburg, Joost; Kazantsev, Daniel; Van Nieuwenhove, Vincent; Lee, Peter; Dobson, Kathy; Sijbers, Jan (2015). "An iterative CT reconstruction algorithm for fast fluid flow imaging". IEEE Transactions on Image Processing. 24 (11): 4446–4458. Bibcode:2015ITIP...24.4446V. doi:10.1109/TIP.2015.2466113. hdl: 10044/1/44267 . PMID   26259219. S2CID   643273.
  14. ↑ Van Nieuwenhove, Vincent; Van Eyndhoven, Geert; Batenburg, Joost; Vandemeulebroucke, Jef; De Beenhouwer, Jan; Sijbers, Jan (2016). "Local Attenuation Curve Optimization (LACO) framework for high quality perfusion maps in low-dose cerebral perfusion CT". Medical Physics. 43 (12): 6429–6438. doi: 10.1118/1.4967263 . PMID   27908148.
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