The Routine CT Protocols at Alkharj Medical Center in Saudi Arabia

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Table of Contents

Introduction
CT scanning protocols of head
High resolution CT of chest (HRCT)
CT scanning protocols of CTA (pulmonary embolism)
CT scanning protocols of liver
CT scanning protocols of pancreas
CT scanning protocols of kidneys
Head CT
Conclusion

Introduction

This assessment aims to demonstrate whether the routine CT protocols at Alkharj Medical Center (AMC) in Saudi Arabia are optimized or not. It also focuses on the best methods of lessening radiation does. The assessment makes a comparison between the AMC protocols against standard protocols provided by the Ministry of Health (MOH) in Saudi Arabia. After a comparison of protocol tables, the assessment explores the available literature to provide accounts of changes in scanning parameters, how such changes have affected patients, a dose of radiation, and the quality of imaging.

CT scanning protocols of head

	1.1 CT scanning protocols of head
	SCGH	SMC
Topogram	AP and Lateral	lateral only
Scan range	From base of the skull to the vertex	From base of the skull to the vertex
Patient position	Supine with head on head rest	Supine with head on head rest
Detectors	64×1.250 mm	24×1.2mm (sequential mode) 64×0.6 mm (spiral mode)
Beam collimation	1.250 mm	1.2 mm and/or 0.6 mm
Gantry rotation time	1.0 second (Sequential mode)	2.5 second (Sequential mode) 1.0 second (Spiral mode)
Slice width	5 mm	4.8 mm for sequential mode 5 mm for spiral mode
Increment for spiral mode	Sequential scan	5 mm
Contrast medium	50 ml Omnipaque 350	50 ml Omnipaque 350
Injection rate	2ml/second automatic injection	Hand injection
Delay time	3-5 minutes	60 seconds
kVp	120-140	120
mAs	Modulated	380 (Effective mAs)

High resolution CT of chest (HRCT)

	1.2 High resolution CT of chest (HRCT)
	SCGH	SMC
Topogram	AP and Lateral	AP only
Scan range	Apex of lung to diaphragm	Apex of lung to diaphragm
Patient position	Supine and arms on head rest	Supine and arms on head rest
Detectors	64×0.625	64×0.6
Beam collimation	0.625 mm	0.6 mm
Gantry rotation time	0.5 second	0.5 second
Slice width	1.250 mm lung window	5 mm0.7 mm reconstruction
IV contrast	None	None
Oral contrast	None	None
kVp	120	120
mAs	Modulated	120 (Effective mAs)

CT scanning protocols of CTA (pulmonary embolism)

	1.3 CT scanning protocols of CTA (pulmonary embolism)
	SCGH	SMC
Topogram	AP and Lateral	AP only
Scan range	From diaphragm to the lower neck	From diaphragm to 3cm above aortic arch
Patient position	Supine with patient’s feet first	Supine with patient’s arms on head rest
Detectors	64×0.625 mm	64×0.6 mm
Beam collimation	0.65 mm	0.6 mm
Gantry rotation time	0.65 second	0.33 second
Slice width	2.5 mm and 0.625 mm reconstruction	5 mm and 0.7 mm reconstruction
Pitch	0.984 mm	0.9 mm
Oral contrast	None	None
IV contrast	80 ml Omnipaque 350 + 20 ml saline	80-100 ml Omnipaque 350
Injection rate	4.5 ml/second	4 ml/second
Delay time	15 seconds + Test bolus	15-20 seconds / 100 HU triggering level
kVp	100	100
mAs	Modulated	130 (Effective mAs)
Bismuth shields	Yes	None

CT scanning protocols of liver

	1.4 CT scanning protocols of liver
	SCGH	SMC
Topogram	AP and Lateral	AP only
Scan range	Portal venous phase: Whole abdomen.	Non contrast: Liver Arterial phase: Liver Venous phase: Whole abdomen
Patient position	Supine feet first	Supine with arms on head rest
Detectors	640.625 mm	Non contrast: 24×1.2 mm Arterial phase: 64×0.6 mm Venous phase: 24×1.2 mm
Beam collimation	Venous phase: 2.5mm	Non contrast: 1.2mm Arterial phase: 0.6mm Venous phase: 1.2mm
Gantry rotation time	0.6 second	0.5 second
Slice width	2.5 mm with 0.625 mm for reconstruction	5 mm with 1 mm for reconstruction
Pitch	1.375 mm	1.4 mm
Delay time	Bolus tracking	Arterial phase: 25 seconds Venous phase: 75 seconds Or bolus tracking (100 HU)
kVp	120	120
mAs	Modulated	200 (Effective mAs)
Bismuth shields	Yes	None
Image order	Craniocaudal	Craniocaudal
Oral contrast	1000 cc water over 20 mins	1000 cc water over 20 mins
IV contrast concentration (mg/ml)	350	350
IV contrast volume (cc)	100-120 cc of Omnipaque 350	100-120 cc of Omnipaque 350
IV contrast injection rate (cc/s)	3-4 cc/sec	3-4 cc/sec
Scan delay (fixed or bolus tracking)	25 sec arterial / 50-60 venous	25 sec arterial / 50-60 venous
Saline chaser (cc)	30 (optional)	30 (optional)
3D Technique used	VRT / MIP using inSpace only	VRT / MIP using inSpace only

Phase type	Non-contrast	Arterial	Venous	Non-contrast	Arterial	Venous
kVp	120	120	120	120	120	120
Effective mAs	140	160	140	200	200	200
Rotation time (sec)	0.5	0.5	0.5	0.5	0.5	0.5
Slice thickness (mm)	5.0	5.0	5.0	0.75	0.75	0.75
Detector collimation (mm)	1.5	0.75	1.5	0.75	0.75	0.75
Feed / Scan (mm)	24.0	9.0	24.0	12.0	12.0	12.0
Kernel	B31f	B31f	B31f	B30f	B30f	B30
Increment (mm)	0.5	0.5	0.5	0.5 – 0.75	0.5 – 0.75	0.5 – 0.75

CT scanning protocols of pancreas

	1.5 CT scanning protocols of pancreas
	SCGH	SMC
Topogram	AP and Lateral	AP only
Scan range	Whole abdomen	Mid stomach to iliac crest
Patient position	Supine with feet first	Supine with arms on head rest
Detectors	64×0.625 mm	Non contrast: 24×1.2 mm Arterial phase: 64×0.6 mm Venous phase: 24×1.2 mm
Beam collimation	Non contrast: 5 mm Arterial phase: 0.625 mm Venous phase: 2.5 mm	Non contrast: 1.2mm Arterial phase: 0.6mm Venous phase: 1.2mm
Gantry rotation time	0.6 second	0.5 second
Slice width	2.5 mm	5 mm with 1 mm for reconstruction
Pitch	0.984 mm	1.4 mm
kVp	140	120
mAs	Modulated	200 (Effective mAs)
Bismuth shields	Yes	None
Image order	Craniocaudal	Craniocaudal
Reconstruction algorithm	Soft tissue (B31f)	Soft tissue (B20f)
Oral contrast	1000 cc water over 20 mins	1000 cc water over 20 mins
IV contrast concentration (mg/ml)	350	350
IV contrast volume (cc)	120 cc of Omnipaque 350	100-120 cc of Omnipaque 350
IV contrast injection rate (cc/s)	3-4 cc/sec	3-4 cc/sec
Scan delay (fixed or bolus tracking)	Arterial phase: 30 seconds Venous phase: 70 seconds	Arterial phase: 25 seconds Venous phase: 75 seconds Or bolus tracking with 100 HU triggering level
Saline chaser (cc)	40 (optional)	40 (optional)
3D Technique used	VRT / MIP using InSpace	VRT / MIP using InSpace only

Phase type	Non-contrast	Arterial	Venous	Non-contrast	Arterial	Venous
kVp	120	120	120	120	120	120
Effective mAs	140	160	140	200	200	200
Rotation time (sec)	0.5	0.5	0.5	0.5	0.5	0.5
Slice thickness (mm)	5.0	5.0	5.0	0.75	0.75	0.75
Detector collimation (mm)	1.5	0.75	1.5	0.75	0.75	0.75
Feed / Scan (mm)	24.0	9.0	24.0	12.0	12.0	12.0
Kernel	B31f	B31f	B31f	B30f	B30f	B30
Increment (mm)	0.5 – 0.75	0.5 – 0.75	0.5 – 0.75	0.5 – 0.75	0.5 – 0.75	0.5 – 0.75
Reconstruction interval (mm)	5×5	1×0.75	1×0.75	5×5	3×3 & 1×0.8	2×2

CT scanning protocols of kidneys

	1.6 CT scanning protocols of kidneys
	SCGH	SMC
Topogram	AP and Lateral	AP only
Scan range	Whole abdomen	Whole abdomen
Patient position	Supine with feet first	Supine with head first
Detectors	64×0.625	64×0.6
Beam collimation	0.625 mm	0.6 mm
Gantry rotation time	0.8 second	0.5 second
Slice width	2.5 mm 0.625 mm for reconstruction	5 mm 1 mm for reconstruction
Pitch	1.375 mm	1.4 mm
Contrast medium	None	None
kVp	120	120
mAs	Modulated	200 (Effective mAs)
Bismuth shields	Yes	None
Reconstruction algorithm	Soft tissue (B20f)	Soft tissue (B20f)
Oral contrast	1000 cc water over 20 mins	1000 cc water over 20 mins
IV contrast concentration (mg/ml)	350	350
IV contrast volume (cc)	100-120 cc of Omnipaque 350	100-120 cc of Omnipaque 350
IV contrast injection rate (cc/s)	3-4 cc/sec	3-4 cc/sec
Scan delay (fixed or bolus tracking)	25 sec arterial / 50-55 sec venous / 240 sec excretory phase	25 sec arterial / 50-55 sec venous / 240 sec excretory phase
Saline chaser (cc)	VRT / MIP using InSpace only
3D Technique used		VRT / MIP using InSpace only

Phase type	Non-contrast	Arterial	Venous	Delay	Non-contrast	Arterial	Venous	Delay
kVp	120	120	120	120	120	120	120	120
Effective mAs	140	160	140	140	200	200	200	200
Rotation time (sec)	0.5	0.5	0.5	0.5	0.5	0.5	0.5	0.5
Slice thickness (mm)	5.0	5.0	5.0	5.0	0.75	0.75	0.75	0.75
Detector collimation (mm)	1.5	0.75	1.5	1.5	0.75	0.75	0.75	0.75
Feed / Scan (mm)	24.0	9.0	24.0	24.0	12.0	12.0	12.0	12.0
Kernel	B31f	B31f	B31f	B31f	B30f	B30	B30	B30
Increment (mm)	5.0	5.0	5.0	5.0	5.0	5.0	5.0	5.0
Reconstruction interval (mm)	3×3	1×0.75	1×0.75	3×3	3×3	3×3 & 1×0.7	3×3	3×3

Head CT

Not many studies exist in the area of lowering the dose for CT of the head. Therefore, the lack of past studies in this field presented challenges because the assessment aimed to compare practices and the standard protocols. Cohen et al. (2000) conducted a study on the image quality changes on CT scan of the head by applying a formalin-fixed cadaver. These researchers reduced the radiation dose by reducing both mAs and kVp on two separate CT machines.

They used both helical scanning mode and the conventional sequential mode. Some researchers evaluated the subjective quality of the image, but they did not note any differences in image quality from different scans performed at the range of 60 percent to 100 percent. The sequential model had a standard mode of (135 kVp + 270 mAs) and (130 kVp + 315 mAs) for two various scanners while the sequential mode had (120 kVp + 185 mAs) and (130 kVp + 157 mAs) for helical scanning.

The researchers noted a linear inverse relationship between the dose and image noise. The study only concentrated on a broad assessment of the subjective quality of the image of a cadaver head without any relation to clinical conditions. Cohen et al. noted that scans produced with a dose that was “more than 50% reduced in comparison with standard settings were considered not interpretable” (Cohnen et al. 2000).

Another study used a 4-MDCT helical CT examination of the head for regular indications. It used the setting of 140 kV, 170 mAs with a scan of one second, and a pitch factor of 0.75 CT dose index weight (CTDIw) with 65 millygray (mGy). The scan was performed a few times by using four images of 5mm thick images at 90 mAs (CTDIw of 34 mGy. There were also similar parameters at four levels:

Posterior fossa
Middle cranial fossa
Corona radiate
Centrum semiovale

The reduction at these four levels was 47 percent. However, the difference between GM and WM was not significantly conspicuous between the two-dose groups. The major GM contrast-to-noise ratio (CNR) was 22% higher in the 170-mAs group. This was statistically significant and considered acceptable diagnostic image quality with a good resolution despite the noise. Some neuro-radiologists believe that it is normal for patients to undergo several CT scans of the head for a certain period based on the degree of the illness in a hospital that has an active neurological intensive care unit and a stroke unit.

These scans usually show gross imaging findings. However, they can influence management decisions when dealing with traumatic or non-traumatic hemorrhage aneurysm rupture, stroke, and hydrocephalus.

Children and other young patients had significant variations between scans with a CTDIw with 65 mGy and of 34 mGy, particularly with repeated scans within a short time. However, a low-dose technique was not suitable for an initial workup because it lacked scientific studies to support its ability to detect subtle pathology (e.g. lacunar infarctions) correctly. Objective measurements did not indicate any significant difference in GM-WM conspicuity in standard and low-dose images with a reduction of about 50 percent. Mullins et al. (2004) note that such differences have subtle distinctions about Hounsfield units than the conspicuity in most lesions.

Britten and colleagues (2004) also concluded a similar result. They worked with spatially correlated statistical noise to standard CT images of the head to replicate a reduction in exposure by up to 50 percent among 23 elderly patients. These researchers simulated images at 300, 260, and 210 mAs by using 120 kV and 420 mAs during the initial scan. They also used periventricular with low-density lesions to act as an indicator of the effect of simulated dose reduction on the precision of the diagnosis.

However, this was not reduced significantly relative to 210-mAs images or about 50 percent dose reduction. They also used visualization of the internal capsule to measure the quality of the image, but this was low in terms of dose image. The low number of research population that participates in the study generally reduces sensitivity (in this case n = 22 and 23).

Gündogdu et al. (2005) analyzed the impact of different tube current settings to enhance the quality of the image and dose for adult head CT among 60 patients. They studied posterior fossa, basal ganglia, and centrum semiovale with aim of reviewing subjective image and noise quality indicators and noise measurements. There was no poor quality score at the level of 50 percent decrease in dose protocol with an initial CTDI of 58.2 mGy for the posterior fossa and 48 mGy for the supra-tentorial. However, a further change at a 60% decrease in dose protocol resulted in a high poor quality score, particularly in the posterior fossa.

These three recent studies show that it is clinically possible to reduce the dose for standard head CT examinations. Moreover, even a reduction in dose by 50 percent did not have any significant effect on the quality of the image. However, these studies focused only on morphological normal anatomical brain areas, but the issue of how much resolution of low-contrast lesions will be affected by low-dose protocols remains unresolved. The eye lens is of importance in the CT of the brain because researchers have investigated and documented cataract formation. According to Heaney and Norvill (2006), the use of various scan planes (with different gantry angulation) to avoid orbits reduces the eye lens dose by 88 percent. This reduction does not have any impact on the severity of posterior fossa artifacts or the hardening of the beam by petrous bones.

X-ray fluency affects the image quality of the CT. As a result, adults and children (young patients) should have different techniques in pediatric CT because young patients attenuate few X-rays. This suggests that physicians can achieve the same image quality by using reduced dose levels. Still, children CT in pediatric use low energy than adults because of small mass and the long-expected lifetime results in the higher dose for children than in adults for the same CT examination (Huda, Walter and Awais 2007).

Siegel and other authors (2004) note that a lower tube current can be effective for maintaining the image quality. Some studies (Shah et al., 2005) have shown that differences in image quality do not occur by using 140 kV and 180–240 mA or a lower dose at 90–130 mA. Still, a reduction between 45% and 50% tube current does not have any significant impact on the quality of the image, and readers have confidence with the available information for making diagnosis decisions. Some researchers propose the use of the maximum anteroposterior diameter of the child’s head (Wong et al., 2001). This can serve as a good standard for measuring tube current at the start of the examination.

On the other hand, Boone et al. (2003) have proposed a significant reduction in dose in the smallest children due to the variations in the patient’s thickness and X-ray attenuation. Children’s bones are less thick and dense. Therefore, it is only reasonable to use a low dose and tube voltage in children. For instance, a reduction from 120 to 80 kV results in a dose reduction of 75%. However, children and infants can use 100 kV on the head CT sufficiently (Siegel et al. 2004).

Conclusion

Elkhart Medical Center (AMC) used various parameters for every protocol. Moreover, it was difficult to make a comparison with the recommended protocol from the MOH identified in the table. For instance, reconstruction measurements differed for both protocols. However, AMC had a slightly high width than the MOH protocols. They also had different detector configurations. Moreover, AMC had high pitch than the MOH pitch protocol. On gantry rotation time, AMC protocols were less than the MOH protocols except for the head protocol (2.5 seconds for AMC and 1.0 seconds for MOH).

It was also difficult to make a comparison between the mAs of both institutions because of the variations in techniques used. The MOH standard proposes the use of modulated mAs, and AMC should use efficient mAs for their protocols. Conversely, kVp protocols were almost the same for all the hospitals. The MOH used Bismuth shields in scans while AMC did not use the shield in scans.

Overall, users can adjust most of the CT scan parameters. However, any change in parameters affects the radiation dose. Users can control these parameters to reduce the dose and enhance the quality of the image to an optimum diagnostic level.

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