Metal artefact reduction in CT imaging of hip prostheses­an evaluation of commercial techniques provided by four vendors.

OBJECTIVE: The aim of this study was to evaluate commercial metal artefact reduction (MAR) techniques in X-ray CT imaging of hip prostheses. METHODS: Monoenergetic reconstructions of dual-energy CT (DECT) data and several different MAR algorithms, combined with single-energy CT or DECT, were evaluated by imaging a bilateral hip prosthesis phantom. The MAR images were compared with uncorrected images based on CT number accuracy and noise in different regions of interest. RESULTS: The three MAR algorithms studied implied a general noise reduction (up to 67%, 74% and 77%) and an improvement in CT number accuracy, both in regions close to the prostheses and between the two prostheses. The application of monoenergetic reconstruction, without any MAR algorithm, did not decrease the noise in the regions close to the prostheses to the same extent as did the MAR algorithms and even increased the noise in the region between the prostheses. CONCLUSION: The MAR algorithms evaluated generally improved CT number accuracy and substantially reduced the noise in the hip prostheses phantom images, both close to the prostheses and between the two prostheses. The study showed that the monoenergetic reconstructions evaluated did not sufficiently reduce the severe metal artefact caused by large orthopaedic implants. ADVANCES IN KNOWLEDGE: This study evaluates several commercially available MAR techniques in CT imaging of large orthopaedic implants.

ICRP Publication 117. Radiological protection in fluoroscopically guided procedures performed outside the imaging department.

An increasing number of medical specialists are using fluoroscopy outside imaging departments, but there has been general neglect of radiological protection coverage of fluoroscopy machines used outside imaging departments. Lack of radiological protection training of those working with fluoroscopy outside imaging departments can increase the radiation risk to workers and patients. Procedures such as endovascular aneurysm repair, renal angioplasty, iliac angioplasty, ureteric stent placement, therapeutic endoscopic retrograde cholangio-pancreatography,and bile duct stenting and drainage have the potential to impart skin doses exceeding Gy. Although tissue reactions among patients and workers from fluoroscopy procedures have, to date, only been reported in interventional radiology and cardiology,the level of fluoroscopy use outside imaging departments creates potential for such injuries.A brief account of the health effects of ionising radiation and protection principles is presented in Section 2. Section 3 deals with general aspects of the protection of workers and patients that are common to all, whereas specific aspects are covered in Section 4 for vascular surgery, urology, orthopaedic surgery, obstetrics and gynaecology,gastroenterology and hepatobiliary system, and anaesthetics and pain management.Although sentinel lymph node biopsy involves the use of radio-isotopic methods rather than fluoroscopy, performance of this procedure in operating theatres is covered in this report as it is unlikely that this topic will be addressed in another ICRP publication in coming years. Information on radiation dose levels to patients and workers, and dose management is presented for each speciality.

Optimizing the tube potential for lumbar spine radiography with a flat-panel digital detector.

The purpose of this study was to find the optimal settings for lumbar spine radiography with a flat-panel detector. A CDRAD contrast-detail phantom was imaged at various tube potentials, system speeds and filtration settings. Factorial experiments yielded a range of optimized exposure settings, which were submitted to visual grading analysis with images of an Alderson phantom. The first optimized settings involved a system speed increase from 400 to 800. For anteroposterior projection, the optimal tube potential was reduced from the default of 77 kV to 60 kV to give the best image quality without increasing the effective dose, or to 66 kV to give the lowest dose without reducing image quality. For lateral projection, the tube potential was similarly reduced from the default of 90 kV to 70 kV or 77 kV. Visual grading analysis confirmed the results, with significantly better image quality when optimizing for image quality. The study thus shows that the tube potential can be reduced as long as the system speed is increased simultaneously. This leads to a lower effective dose and/or increased image quality depending on the settings chosen. The factorial experiments provided a powerful way to evaluate several parameters concomitantly.

Impact of digital imaging on radiation doses to the patient during X-ray examination of the urinary tract.

PURPOSE: To compare radiation doses given to patients undergoing IVU (intravenous urography) before and after digitalization of our X-ray department. MATERIAL AND METHODS: IVU examinations were monitored with dose area product meters before and after the X-ray department changed to digital techniques. The first step was a change from film-screen to storage phosphor plates, while the second step involved changing to a flat panel detector. Forty-two patients were included for the film-screen situation, 69 when using the storage phosphor plates, and 70 using the flat panel detector. RESULTS: A dose reduction from 41.8 Gycm2 to 31.5 Gycm2 was achieved with the first step when the film-screen system was replaced with storage phosphor plates. A further reduction to 12.1 Gycm2 was achieved using the flat panel detector. CONCLUSION: The introduction of the flat panel detectors made a considerable dose reduction possible.

A clinical evaluation of the image quality computer program, CoCIQ.

To provide an objective way of measuring image quality, a computer program was designed that automatically analyzes the test images of a contrast-detail (CD) phantom. The program gives a quantified measurement of image quality by calculating an Image Quality Figure (IQF). The aim of this work was to evaluate the program and adjust it to clinical situations in order to find the detectable level where the program gives a reliable figure of the contrast resolution. The program was applied on a large variety of images with lumbar spine and urographic parameters, from very low to very high image qualities. It was shown that the computer program produces IQFs with small variations and there were a strong linear statistical relation between the computerized evaluation and the evaluation performed by human observers (R2= 0.98). This method offers a fast and easy way of conducting image quality evaluations.

Radiation risk and cost-benefit analysis of a paediatric radiology procedure: results from a national study.

A national study was performed to investigate radiation doses and associated risks to patients during X-ray fluoroscopy-guided small intestinal biopsies in the investigation of coeliac disease. Thermoluminescent dosemeters (TLD) and questionnaires were sent to 42 of the 43 paediatric departments in Sweden performing these biopsies. During the study period (2 x 3 weeks) 257 biopsies were recorded, representing about 10% of annually performed paediatric investigations. The results show that the absorbed dose during biopsy ranged from 0.04 mGy to 23.8 mGy (mean 1.87 mGy). The fluoroscopy time ranged from 2 s to 663 s (mean 60 s). The collective dose from the procedure amounts to 4.7 manSv year(-1). Thus, the annual excess cancer mortality, including severe hereditary effects, can be estimated at 0.6-0.7 cases per year. However, significant dose saving can be obtained by proper choice of sedation and biopsy equipment.

Dose reduction in computed tomography by individualized scan protocols.

PURPOSE: To find a method of adjusting the mAs-value in relation to the size of the patient undergoing computed tomography (CT) examination as a means of minimizing the radiation dose to the patient. MATERIAL AND METHODS: A correction factor to be applied on the tube charge for each patient was calculated using two mathematical methods. This approach was tested on 4 Perspex phantoms of different sizes and geometries. Noise was measured in the images with and without use of the correction factors. Retrospectively, correction factors were calculated for 12 CT examinations of the abdomen and the dose reduction was estimated for these patient studies. RESULTS: The variations in noise measured in the images of the different phantoms were dramatically reduced by both methods. The retrospectively performed patient study showed that the largest correction factor was 7 times greater than the smallest, which means that a dose reduction factor of 7 is possible in the extreme case. CONCLUSION: Our proposed methods of adjusting the applied tube charge (mAs-value) in relation to the size of the patient can be used on the vast majority of CT systems. The potential for dose reduction is great, especially for small patients.

Image quality vs. radiation dose for a flat-panel amorphous silicon detector: a phantom study.

The aim of this study was to investigate the image quality for a flat-panel amorphous silicon detector at various radiation dose settings and to compare the results with storage phosphor plates and a screen-film system. A CDRAD 2.0 contrast-detail phantom was imaged with a flat-panel detector (Philips Medical Systems, Eindhoven, The Netherlands) at three different dose levels with settings for intravenous urography. The same phantom was imaged with storage phosphor plates at a simulated system speed of 200 and a screen-film system with a system speed of 160. Entrance surface doses were recorded for all images. At each setting, three images were read by four independent observers. The flat-panel detector had equal image quality at less than half the radiation dose compared with storage phosphor plates. The difference was even larger when compared with film with the flat-panel detector having equal image quality at approximately one-fifth the dose. The flat-panel detector has a very favourable combination of image quality vs radiation dose compared with storage phosphor plates and screen film.

Radiographic joint space narrowing and histologic changes in a rabbit meniscectomy model of early knee osteoarthrosis.

The purpose of this study was to compare weightbearing radiographs with histologic cartilage evaluation in a rabbit meniscectomy model of the early stage of osteoarthrosis. Fifteen rabbits had a medial meniscectomy performed in one knee and a sham operation in the other knee. Five rabbits each were sacrificed at 13, 25, and 40 weeks after surgery. Radiographic joint space width and histologic cartilage changes of the medial knee compartment were quantified. Five non-operated knees and five knees in which the meniscus had been removed immediately before the evaluations served as control specimens. Overall, the joint space of the peripheral part of the medial knee compartment was narrower in knees operated on for meniscus removal than in sham-operated knees (P < 0.003). In the knees with the meniscus removed, more cartilage changes were seen at the joint surface area of contact on radiographs than in the sham-operated knees (P < 0.0015). Indeed, the area of contact had cartilage changes similar to those in the whole medial compartment. However, there was no correlation between the degree of histologic cartilage change and the corresponding joint space measurements. Joint space width as measured on weightbearing radiographs is reduced after meniscectomy in the rabbit, but it does not reflect the degree of cartilage damage of the loaded joint surfaces in early stages of osteoarthrosis.

Digital radiography of scoliosis with a scanning method: initial evaluation.

PURPOSE: To evaluate the radiation dose, image quality, and Cobb angle measurements obtained with a digital scanning method of scoliosis radiography. MATERIALS AND METHODS: Multiple images were reconstructed into one image at a workstation. A low-dose alternative was to use digital pulsed fluoroscopy. Dose measurements were performed with thermoluminescent dosimeters in an Alderson phantom. At the same time, kerma area-product values were recorded. A Monte Carlo dose calculation also was performed. Image quality was evaluated with a contrast-detail phantom and visual grading system. Angle measurements were evaluated with an angle phantom and measurements obtained on patient images. RESULTS: The effective radiation dose was 0.087 mSv for screen-film imaging, 0.16 mSv for digital exposure imaging, and 0.017 mSv for digital fluoroscopy; the corresponding kerma area-product values were 0.43, 0.87, and 0.097 Gy. cm(2), respectively. The image quality of the digital exposure and screen-film images was about equal at visual grading, whereas fluoroscopy had lower image quality. The angle phantom had lower angle values with digital fluoroscopy, although the difference in measured angles was less than 0.5 degrees. The patient images showed no difference in angles. CONCLUSION: The described digital scanning method has acceptable image quality and adequate accuracy in angle measurements. The radiation dose required for digital exposure imaging is higher than that required for screen-film imaging, but that required for digital fluoroscopy is much lower.

Mobile computerized tomography scanning in the neurosurgery intensive care unit: increase in patient safety and reduction of staff workload.

OBJECT: Transportation of unstable neurosurgical patients involves risks that may lead to further deterioration and secondary brain injury from perturbations in physiological parameters. Mobile computerized tomography (CT) head scanning in the neurosurgery intensive care (NICU) is a new technique that minimizes the need to transport unstable patients. The authors have been using this device since June 1997 and have developed their own method of scanning such patients. METHODS: The scanning procedure and radiation safety measures are described. The complications that occurred in 89 patients during transportation and conventional head CT scanning at the Department of Radiology were studied prospectively. These complications were compared with the ones that occurred during mobile CT scanning in 50 patients in the NICU. The duration of the procedures was recorded, and an estimation of the staff workload was made. Two patient groups, defined as high- and medium-risk cases, were studied. Medical and/or technical complications occurred during conventional CT scanning in 25% and 20% of the patients in the high- and medium-risk groups, respectively. During mobile CT scanning complications occurred in 4.3% of the high-risk group and 0% of the medium-risk group. Mobile CT scanning also took significantly less time, and the estimated personnel cost was reduced. CONCLUSIONS: Mobile CT scanning in the NICU is safe. It minimizes the risk of physiological deterioration and technical mishaps linked to intrahospital transport, which may aggravate secondary brain injury. The time that patients have to remain outside the controlled environment of the NICU is minimized, and the staff's workload is decreased.

A comparison of analogue and digital techniques in upper gastrointestinal examinations: absorbed dose and diagnostic quality of the images.

This study was performed to investigate whether patient exposure and diagnostic quality of the image is significantly influenced by the introduction of digital image acquisition techniques. Evaluation was performed for three different techniques (analogue, analogue fluoro + digital radiography, digital) in examination of the upper gastrointestinal tract. The evaluation was done from data acquired in three different departments. Patient exposure was recorded as KERMA-area product (KAP) and the individual patient readings were normalised to a standard size patient. Image quality was assessed using visual grading with a reference image. The recorded KAP values were significantly higher (22.3 Gycm2) for the fully digital technique compared to the others (analogue 6.8 Gycm2, analogue + digital 3.6 Gycm2). This was due mostly to an increased number of exposures. The diagnostic quality of the image was, however, also regarded to be slightly lower for the technique giving the lowest patient dose with the smallest number of exposures (analogue + digital). The digital examination technique, as used in this study, thus resulted in significantly higher patient dose without any significant gain in diagnostic quality of the image.

Patient radiation exposure during coronary angiography and intervention.

PURPOSE: To prospectively register fluoroscopic and cine times in a random fashion, and to measure patient radiation exposure from routine coronary angiography and coronary balloon angioplasty. We also evaluated an optional dose reduction system used during interventions. MATERIAL AND METHODS: The incident radiation to the patient was measured as kerma area product (KAP) in Gycm(2), obtained from an ionisation chamber mounted on the undercouch tube during 65 coronary angiography procedures and another 53 percutaneous transluminal coronary angioplasties (including 29 stent procedures), mostly directly following complete coronary angiography. RESULTS AND CONCLUSION: The values from coronary angiography were comparable to other reports with a mean fluoroscopic time of 4.4 min and a mean KAP value of 62.6 Gycm(2). The corresponding figures from coronary balloon angioplasty without stenting were lower than otherwise reported, with 8.2 min and 47.9 Gycm(2), respectively. The use of coronary stents did prolong the mean fluoroscopic time (10.5 min) but did not significantly enhance the patient mean radiation dose (51.4 Gycm(2)). The dose reduction technique resulted in a significant KAP value reduction of 57%. In conclusion, with regard to radiation exposure, coronary angiography and balloon angioplasty are considered safe procedures.

Sensitivity of coefficients for converting entrance surface dose and kerma-area product to effective dose and energy imparted to the patient.

We investigate the sensitivity of the conversions from entrance surface dose (ESD) or kerma-area product (KAP) to effective dose (E) or to energy imparted to the patient (epsilon) to the likely variations in tube potential, field size, patient size and sex which occur in clinical work. As part of a factorial design study for chest and lumbar spine examinations, the tube potentials were varied to be +/-10% of the typical values for the examinations while field sizes and the positions of the field centres were varied to be representative of values drawn from measurements on patient images. Variation over sex and patient size was based on anthropomorphic phantoms representing males and females of ages 15 years (small adult) and 21 years (reference adult). All the conversion coefficients were estimated using a mathematical phantom programmed with the Monte Carlo code EGS4 for all factor combinations and analysed statistically to derive factor effects. In general, the factors studied behaved independently in the sense that interaction of the physical factors generally gave no more than a 5% variation in a conversion coefficient. Taken together, variation of patient size, sex, field size and field position can lead to significant variation of E/KAP by up to a factor of 2, of E/ESD by up to a factor of 3, of epsilon/KAP by a factor of 1.3 and of epsilon/ESD by up to a factor of 2. While KAP is preferred to determine epsilon, the results show no strong preference of KAP over ESD in determining E. The mean absorbed dose D in the patient obtained by dividing epsilon (determined using KAP) by the patient's mass was found to be the most robust measure of E.

Use of the concept of energy imparted in diagnostic radiology.

The concept of energy imparted by ionizing radiation to the matter in a volume is analyzed and methods to determine the energy imparted epsilon to the patient are reviewed, in particular, determinations based on measurements of the air kerma integrated over beam area [the kerma-area-product (KAP)] and calculations needed to derive conversion factors epsilon/KAP. The energy imparted to the image receptor, epsilon rec, including the statistical aspects of the concept, and the effect of epsilon rec on image quality and patient dose are also analysed. Finally, use of the energy imparted to the patient as a risk indicator is discussed.

Ionization chambers for measuring air kerma integrated over beam area. Deviations in calibration values using simplified calibration methods.

Calibrations of kerma-area product meters (KAP meters) are often performed using simplified methods. The accuracy thus obtained can be insufficient, especially when the KAP meters are used for optimizing radiological procedures. The deviations between the best available calibration factor (k) and the simplified calibration factor (ks) were measured at different clinical x-ray installations. Depending on the type of x-ray installation and calibration method, the quotient ks/k ranged from 0.83 to 1.19, reflecting the error made in practice using these methods. A simple alternative calibration method based on comparison with a KAP meter calibrated by the best available method is described. Depending on tube potential and the stability of the electrometers, the uncertainty in the calibration factor derived with this method was between 3.8% and 5.6% (at 95% confidence level).

Absorbed dose and image quality in examinations of the colon with digital and analogue techniques.

PURPOSE: Image quality and the absorbed dose to the patient are issues of primary interest in the change-over from the conventional analogue technique to the digital technique in the examination of the colon by means of fluoroscopy. The aim of this study was to compare the incident radiation and to evaluate the image quality in two different X-ray equipment types, one digital and one analogue. MATERIAL AND METHODS: A kerma-area product meter was used to measure the incident radiation to the patient. Both fluoroscopy and total-examination times were measured as was the number of images. An evaluation of image quality was made and statistically analysed. RESULTS AND CONCLUSION: No significant difference in the irradiation dose was observed between the two techniques. The fluoroscopy time was significantly lower with the conventional technique but the total-examination time decreased by 18% with the digital technique. The total number of images taken was higher with the digital technique (25 images compared to 19) owing to the limited field of the image intensifier. Significantly more noise and less sharpness were observed with the digital system but there was no significant difference in contrast or image quality in the various anatomical structures. Although the change-over to the digital system produced a reduction in sharpness and an increase in noise, and no significant dose saving was measured, the digital system was faster to work with and could well be used for diagnostic purposes.

Added copper filtration in digital paediatric double-contrast colon examinations: effects on radiation dose and image quality.

Paediatric double-contrast barium enema examinations are usually performed at high tube voltage, 102-105 kV. The aim of this study was to investigate how much the effective dose to the child could be reduced by increasing the X-ray energy further by adding copper filter in the beam, and if this dose reduction could be achieved without endangering image quality. Organ doses to an anthropomorphic phantom simulating a 1-year-old child was measured using thermoluminescence dosimetry for assessment of the effective dose and this value was compared with the energy imparted which was obtained from kerma-area product measurements. To verify that the image quality achieved with this added filtration was still diagnostically acceptable, the study included 15 patient examinations. Since the increased X-ray energy will most probably affect low-contrast objects, image quality was also evaluated with two different phantoms containing low-contrast objects. Effective dose for a complete examination can be decreased 44 % and energy imparted 77 % when a 0.3-mm copper filter is inserted in the beam at tube voltage 102 kV. The patient study did not show any significant deterioration of image quality, whereas phantom measurements of contrast-detail resolution and signal-to-noise ratio was marginally impaired by the added copper filtration. This technique is now in clinical practice for paediatric colon examinations.

The developmental skeletal growth in the rat foot is reduced after denervation.

It has long been known that bone is innervated. In recent years it has been suggested that the local nerves may influence the growth and metabolism of bone by way of neuropeptides. The transient local presence of nerve-containing cartilage canals just before formation of secondary ossification centres in rat knee epiphyses seems to support that view. The purpose of the present study was to see if denervation affects the developmental growth of metatarsal bones in the rat hindfoot. We made sciatic and femoral neurectomies in 7-day-old rat pups and examined the hindfeet at various times after surgery. Immunohistochemical analysis showed that denervation was complete. Radiographic examination revealed that the metatarsal bones were significantly shorter in denervated hindfeet 30 days after denervation (average relative shortening 9.9 +/- 2.3%). Measurements of total foot length showed that denervated feet were subnormally sized already five days postoperatively, before the onset of secondary ossification. The timing of the latter was not affected by denervation. Control rats subjected to tenotomies exhibited normal metatarsal bone lengths. On the basis of these results we suggest that the local nerves may influence the growth of immature bones but do not affect secondary ossification.

The use of carbon fibre material in radiographic cassettes: estimation of the dose and contrast advantages.

A Monte Carlo simulation has been used to estimate the dose and contrast advantages of replacing radiographic cassette fronts fabricated from aluminium with cassette fronts fabricated from low atomic number material (carbon fibre). The simulation used a realistic imaging geometry and calculations were made both with and without an anti-scatter grid. Account was taken of the scatter generated in the cassette front and the effect of beam hardening on primary contrast. Dose and contrast were evaluated for a range of cassette front thicknesses and tube potentials (60-150 kV) as well as for four examinations representative of situations with varying amounts of scatter. The results with an anti-scatter grid show a clear dose and contrast advantage in all cases when an aluminium cassette front is replaced with a low attenuation cassette front. The contrast advantage is dependent upon the examination and is generally greater for imaging bony structures than for imaging soft tissue. If a 1.74 mm aluminium cassette front is compared with a 1.1 mm carbon fibre cassette front, then the dose advantages are 16%, 9%, 8% and 6% and the contrast advantages are 10%, 7%, 4% and 5% for the AP paediatric pelvis examination at 60 kV, the anteroposterior (AP) lumbar spine examination at 80 kV, the lateral lumbar spine examination at 100 kV and the posteroanterior (PA) chest examination at 150 kV, respectively. The results without an anti-scatter grid show an increased dose advantage when a low attenuation cassette front is used, but the contrast advantage is small and in some situations negative.