Introduction
Better Health Channel defines a CT scan as A computed tomography (CT) scan is a medical imaging procedure that uses x-rays and digital computer technology to create detailed two or three-dimensional images. Unlike other forms of medical imaging, the CT scan can image every type of body structure at once including bone, blood vessels and soft tissue. In this assignment I will collect the routine protocols of Head, Chest (HRCT, PE), abdomen (liver, pancreas, spleen and kidneys) from my hospital back in Saudi Arabia “King Khalid General Hospital KKGH” and then I will compare these protocols with other protocols recommended by the literature review. The protocols recommended by the literature review will be referred to in this report as “Other Clinic Reference OCR”. In addition to this I will also discuss whether these protocols are optimized in terms of radiation dose and image quality.
Generally, a high dose increases image resolution, whereas a low dose causes higher image noise. This results in unsharp images. When this occurs it renders reduction of radiation exposure to become difficult. Current attempts for adjusting this are being carried out by using new software technologies. These techniques reduce noise; and apply radiation dose according to individual patient characteristics. This also assists in the evaluation of whether a safer technique other than CT can be used. Some important works on radiation dosage optimization in general are discussed; Van Unnik et al (1997) undertook an inventory of radiation doses in 18 Dutch hospitals.
They also found that several hospitals in the Netherlands did not using adequate IV contrast material. The scan should be performed only when absolutely necessary. For smaller patients, tube current can be reduced. Scan boundaries should be restricted to the area of interest. IV contrasts can be used more liberally to optimize diagnostic yield. These findings agree with those of Donelly et al (2001). User-selectable exposure factors for some common types of examinations using the same model CT scanner at different hospitals were evaluated. Patient size can be used as a parameter for dose reduction with a selection of exposure parameters.
Dose optimization can be achieved by close collaboration among radiographers, physicians and radiologists. (Koller et al 2003). The median effective dose is now significantly lower for screening protocols than daily practice protocols. Liedenbaum et al (2008). These results clearly demonstrate the availability of dosage reduction protocols for most CT scans.
The following protocols from King Khalid General Hospital KKGH and other protocols recommended by Other Clinic Reference OCR can be seen below in addition to the different operational protocols.
*Protocols with different settings for supine and prone. Total effective dose is sum of supine and prone dose.
No screening or surveillance is done in OCR. Hence the related protocols do not apply in the case of OCR. There are significant variations between the KKGH and OCR with respect to certain parameters. In comparing both KKGH and OCR the following was taken into consideration. These considerations were age, gender, pregnancy, height, weight and other demographic features and health conditions of the patient for dose adjustments. The main focus was for the radiation risk to be minimized. In this next part of this paper different aspects of protocols will be reviewed including the assistance of reported work.
Image analysis models
Unless the scan images are analysed and interpreted properly, prognosis and treatment are not possible. Many manual systems exist. Recently some attempts have been made for automated modelling for these requirements as well as for radiation dose reduction. Taking common image analysis tools, an automatic programme for rapid and reliable segmentation and analyse body composition for large scale use.
The authors segmented and quantified muscle, visceral and subcutaneous adipose tissues using shape modelling technique of skeletal muscle (Chung et al 2009). Liu et al (2008) developed a model for 3-D segmentation of bones in joints in MR and CT images of motion analysis. This two-step method allows large scale handling of such cases as the additional operator time is only minimal compared to conventional manual technique. The technique is useful for computer assisted biomechanical modelling and analysis, surgery planning and image-guided surgery of joints. A review of dual energy CT for its uses by Graser et al (2009) listed differentiation of materials and tissues, abdominal imaging, evaluation of renal masses, liver lesions, urinary calculi, small bowel, pancreas and adrenal glands. In angiography, bones can be removed from data sets.
There are many other potential uses. Continuing on this Sommer et al (2010) found dual energy CT can detect endoleaks in a single acquisition. This increases the scope for dose reduction for patients who need to undergo lifelong follow-up evaluations after endovascular aneurysm repair. Clearly more studies on such models to prove their validity and feasibility of using in prognosis and treatment are needed. Many models based on modelling theories are yet to be tested.
Head Scan
Most research works have been reported on stroke and head injuries. A selected few are reviewed below. High speed, multi-section, helical CT scanners are able to perform safe imaging of the entire vascular axis in acute stroke patients by combining CT imaging, CT perfusion imaging and CTA, noted Smith et al (2003). Brott et al (1997) used CT scans to study early haemorrhage growth with intra-cerebral haemorrhage as it is associated with neurological deterioration. Substantial parenchymal haemorrhage occurred within one hour baseline observation. The CT scans were done with standard imaging protocols using 512 x 512 matrix, 8 to 10 mm slices.
Routine early CT scan of patients with minor head injury was recommended by Ingebrigtsen & Romner (2009). Those with normal CT findings and other normal parameters can be discharged. This will reduce the number of in-patients and costs by about 43%. Using CT scans, Kharitonova et al (2009) observed poor prognosis in patients with persistent MCA occlusion after intravenous thrombolysis suggesting alternate treatment approach in such cases. Steyerberg et al (2008) wanted to get a reliable prediction tool on admission of patients with traumatic brain injury using data at admission stage.
The strongest predictors of outcome were age, motor score, papillary reactivity and CT characteristics. The model predictions may support clinical practice. Both internal and external validations were done. Imaging method, scans for early internal symptoms, prognosis at admission stage and at later stages have been subjected to research. These provide adequate coverage of all practical aspects related to head CT scan. The protocols of a head CT scan include collimation of 0.625 mm, rotation time (s) / table speed (mm/s) / pitch of 0.6 / 13.75 / 1.375, display slice thickness (mm) / interval (mm) of 5 / 5, kV/mA of 140/380, a soft reconstruction type and a matrix of 512 / 512 (Halpin 2004).
Chest Scan
CT has become the first choice imaging test for patients who are suspected to have pulmonary embolism (PE). The use of CT for pulmonary circulation imaging has facilitated a major improvement in the visualization of peripheral pulmonary arteries and detection of small emboli (Scheopf et al, 2004). CT has received wide spread application in clinical practice due to its numerous advantages, the most outstanding being the ability to evaluate the “mediastinal and parenchymal structures” (Scheopf et al, 2004).
This has made it possible to the radiologist to directly visualize the thrombus. There are different protocols that can be used to study PEs. In a study conducted by Schoepf et al, the diagnosis of PE is excellent when spiral CT angiography (k =0.72) is utilized (2004). However, moderate results are achieved when the same is applied for “ventilation-perfusion lung scanning (k= 0.22)” (Nieman et al, 2001). Studies conducted indicate that the use of conventional CT protocols may lead to missing of a PE at the segmental arterial level.
The accuracy however varies depending on the type of CT. For instance, the accuracy is seen to increase from the single detector row, dual detector row, and finally to electron beam CT scanners (Scheopf et al, 2004). However this only represents an increase to about 60 percent implying that there are still challenges. Some of these challenges have been overcome by the development of the multi-detector row CT (Pirker et al, 2009). This allows the visualization of the whole “chest with 1-mm resolution within a short single breath-hold (<10 seconds)” (Scheopf et al, 2004)
Improved visualization of the pulmonary arteries has been achieved by the use “thin section multi-detector row CT protocols. The use of high-quality multi-detector row CT scans minimizes the overall radiation burden in the patient” (Scheopf et al, 2004). This is due to the fact that more test activities requiring the use of ionizing radiation are less needed when this protocol is applied. For instance, if the four-detector row CT protocol with 5-mm collimation is used then the radiation dose is seen to increase by 30% to 100% (Scheopf et al, 2004).
The increase is mainly attributed to other tests that require the use of ionizing radiation when this protocol is used. Adding extra detector elements leads to increased tube output utilization, this is seen when the 16- detector row CT with sub-millimetre capabilities is used as opposed to the conventional four-detector row scanners (Scheopf et al, 2004). As the HRCT become part of the routine clinical practice a substantial reduction in dose will be achieved without necessarily affecting the diagnostic quality.
Abdomen Scan
An abdominal CT scan is conducted to identify whether the patient is suffering from “cysts, abscesses, enlarged lymph nodes, foreign objects, bleeding in the belly, appendicitis inflamotory bowel disease among other conditions” (Kalra et al, 2002). CT accounts for a small percentage of x- ray based diagnosis, however, it releases most of the radiation dose associated with medical imaging. Current research is aimed at developing protocols that will utilize lower doses without compromising the quality of radio imaging examinations. Although the use of low-dose radiation has received a lot of backing, a comprehensive evaluation framework for the reduced-dose abdominal CT has not been thoroughly researched (Kalra et al, 2002).
Available literature indicates that patients with lower weight can be diagnosed using reduced radiation doses without compromising the quality of the images. In effect this finding seems to suggest that the range of tube utilized in the conventional protocols should be increased (Pirker et al, 2009). However, in a study conducted by Kalra et al it was established that reducing the dose by a bigger margin such as 50% leads to the production of poor images that are not diagnostically beneficial (2002). Low contrast lesions are likely to be missed due to the increased noise. This has been identified as a major impediment as many radiation centres prefer to use conventional imaging protocols that use standard doses even though they are more harmful to the patients (Pirker et al, 2009).
The multi-phase liver scan is utilized in the detection and characterization of liver lesions. These lesions have different enhancing properties in the different phases depending on whether they are hypo-vascular or hyper-vascular (Zoetelief et al 1998). The pre-contrast liver scan is employed to detect different conditions such as “calcifications, haemorrhages and lesions”( Fishman, 2001). This protocol is utilizes a contrast injection that is tracked and measured at different times depending on the enhancement.
Spiral CT offers many advantages in organ assessment. For instance, a complete assessment of the liver, spleen and pancreas can often be achieved using the spiral CT. This protocol eliminates data “misregistration and enables the visualization of the entire kidney during peak contrast or other desired enhancements” (Zoetelief et al 1998). Spiral CT can be regarded as a low dose CT since it offers “limited anode heat capacity and cooling rate which makes its tube current to be lower than the conventional slice by slice scanning”. However, as seen earlier, the reduction in tube current leads to the production of poor images.
This should be regarded as technical challenge for the spiral CT rather than effect observed when a low dose is utilized. There is so much data about the Spiral CT but there is scanty details regarding patient dose in to this protocol. Thus “clinical evaluation of the potential dose reduction by optimization of the pitch, tube current, and the application of special dose-efficient procedures should be investigated further” (Zoetelief et al 1998).
Summary of literature review
Computed Tomography offers the following advantages as compared to the traditional radiography: CT eliminates superimposition of images outside the area of interest completely; its inherent high contrast ability makes it possible to differentiate between tissues that differ in density; multi-planar reformatted imaging makes CT scans possible to use a single imaging procedure consisting of either multiple contiguous or helical scan for viewing in axial, coronal or sagittal planes as per diagnostic necessities; CT is able to replace many conventional and invasive techniques with better accuracy and efficiency; CT and related scanning technologies can be successfully employed for prognosis and treatment regimes and monitoring; Methods to select suitable contrast media and optimise dose, volume and method of administration with or without adjuncts like saline flush or single/multiple bolus tracking can effectively used for image enhancement as well as radiation dose reduction; Other specific methods for reduction of radiation exposure are also available.
Special caution is advised against indiscriminate use of CT and its use on children and pregnant women; Modelling techniques can be gainfully used for segmentation and analysis of body components in automated systems. These are useful in prognosis and treatment monitoring.
However, there are disadvantages too such as: demand for higher efficiency compromises radiation safety issues; a possible relationship of radiation dose and cancer favours reduced use of CT among children and pregnant women. Children exposed to CT scans, especially of helical type, are prone to cancer to a greater extent as their life span is longer; American College of radiology claims that the life expectancy of CT scan patients is not the same as general.
This shows life expectancy reduces in CT patients due to which it decreases; many unnecessary CT scans are performed now. Sometimes it is used in place of safer ones like ultrasound or magnetic resonance. All the disadvantages are related to radiation safety. There are claims that compared to the advantages the risks are only very low. Typical effective doses of various diagnostic/imaging methods are given in Table 1.
The average background exposure in UK is 1-3 mSv per year.
Even in the case of an accurate technique like CT scan, artefacts can decrease its accuracy and reliability. Motion during the scan and insufficient X-ray tube current or penetration can cause aliasing or streaking by producing blurred lines radiating from the corners. Use of thicker slices can lead to partial volume effects, blurring over the edges. Detector fault can lead to ring effects. Low signal to noise ratio can lead to graining of the image. Windmill streaks appear when detectors intersect with reconstruction planes. Filters can be used to prevent this. Cupped appearance of more attenuation at the centre can be avoided by using filters and software.
Comparison of Khalid General Hospital KKGH and the Other Clinic Reference OCR
Based on the literature reviewed above, the two setups were compared on the basis of protocols applied. The comparison mainly focused on the safety aspect of the protocols utilized at the KKGH and the ones reviewed in the literature.
From the above literature it had been identified that reduction of the radiation dose is an important step towards patient safety. The hospital I am attached to makes use of suitable conventional protocols but has not adopted strategies to reduce the radiation dose. It is however located in a remote area. The KKGH is not getting much scans to do. Hence some lethargy has developed among its health care staff. Due to this, adequate attention is not paid to details of protocols to be followed in each aspect. The KKGH merely survives on the patients from nearby localities who suffer only from ordinary ailments like fever, cough etc. In conclusion there is no much to compare with the reviewed protocols.
Conclusions
The literature reviewed above has shown the availability of many protocols for scanning and imaging, contrast medium optimisation, prognosis and treatment, including the after care of patients. Radiation safety being one of the most important issues, as it needs to be addressed with all seriousness attention. In addition to this the conduction of unnecessary CT scans and the scanning of children and pregnant women need to be controlled to reduce radiation burden. But most importantly research should be conducted to identify how the radiation dose can be reduced without compromising the quality of the images produced. Further to this treatment of elderly people all requires special attention. There is scope for greater improvement in all these respects for KKGH which I personally see as an important recommendation in the future.
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