Phantom development for radiographic image optimization of chest,skull and pelvis examination for nonstandard patient

The construction of the adapted patient equivalent phantom (APEP) to simulate the X-ray scattering and absorption by chest, skull and pelvis of nonstandard patient in conventional radiographic equipment is presented. This APEP system is associated to the pre-existing realistic-analytic phantom (RAP) [Pina, D.R., Duarte, S.B., Ghilardi Netto, T., Trad, C. S., Brochi, M.A.C., Oliveira, S.C. de, 2004. Optimization of standard patient radiographic images for chest, skull and pelvis exams in conventional X-ray equipment. Phys. Med. Biol. 49, N215–N226] forming the coupled phantom (RAP–APEP), which is used to establish an optimization process of radiographic images of chest, skull and pelvis for nonstandard patients. A chart of the optimized radiographic technique is established covering a wide range of nonstandard patient thickness, and offering a dose reduction in comparison with those techniques currently used. Different validation processes were applied to confirm the improving of the radiographic image quality when techniques of the established chart are used.     

Strategies for formulating appropriate MDCT techniques when imaging the chest, abdomen, and pelvis in pediatric patients

OBJECTIVE: Our aim was to formulate appropriate MDCT chest and abdominopelvic CT scan protocols for pediatric patients. MATERIALS AND METHODS: Surface radiation dose measurements from a set of anthropomorphic phantoms (nominal 1 year old, 5 year old, and 10 year old) and an adult phantom were compared with standard CT dose index measurements. Image-noise values on axial 5-mm-thick anthropomorphic phantom images were obtained as a measure of image quality. RESULTS: Peripheral CT dose index values obtained with the standard 16-cm acrylic phantom were within approximately 10% of the CT surface dose measurements for the pediatric anthropomorphic phantoms for both chest and abdominopelvic scan protocols. The noise value for the adult phantom image acquired using a typical clinical CT technique was identified, and targeting this level of noise for pediatric CT examinations resulted in a decrease in dose of 60-90%. Initially, 80 kVp was selected for use with very small children; however, beam-hardening artifacts were severe enough to cause us to abandon this option. Current pediatric protocols at M. D. Anderson Cancer Center rely on 100- and 120-kVp settings. The display field-of-view parameter can be used as a surrogate for patient size to develop clinical pediatric CT protocol charts. CONCLUSION: CT dose index measurements obtained using the 16-cm standard acrylic phantom are sufficiently accurate for estimating chest and abdominopelvic CT entrance exposures for pediatric patients of the same approximate size as the anthropomorphic phantoms used in this study. Image-noise measurements can be used to adjust chest and abdominopelvic CT techniques for pediatric populations, resulting in a decrease in measured entrance dose by 60-90%.     

Xenon versus ceramics: a comparison of two CT X-ray detector systems.

PURPOSE: The purpose of this work was to compare image quality in phantom and patient CT scans acquired by xenon and ceramic CT detector systems. METHOD: High and low contrast resolution and image noise were determined with a standard CT phantom for both detector systems. In patient CT images, the effect on image noise was measured in anatomical regions of interest in the head, lumbar spine, chest, and abdomen. RESULTS: In phantom studies, image noise was significantly lower using ceramic versus xenon detectors. Also, in images of the head and lumbar spine, the signal-to-noise ratio was significantly higher with ceramic than with xenon detectors. In chest scans, ceramic significantly reduced beam-hardening artifacts caused by the thoracic spine. However, in abdominal images, the signal-to-noise ratio was not significantly different between ceramic and xenon detector systems. CONCLUSION: For reduced image noise in CT images of the head, lumbar spine, and chest and high resolution CT, ceramic detector systems appear to be superior to xenon detector systems.     

AMBER and conventional chest radiography: comparison of radiation dose and image quality.

The authors compared the radiation dose to the patient and the image quality in advanced multiple-beam equalization radiography (AMBER) with those in conventional chest radiography. Organ doses were estimated for an anthropomorphic phantom from measurements with thermoluminescence dosimeters. These measurements were supplemented with area-air kerma products obtained during chest examinations of 223 patients. Image quality was determined by means of a contrast-detail image evaluation test. An improvement in image quality in regions of high absorption and an increased dose to the patient were found for the AMBER technique compared with the conventional technique. However, for both techniques, the radiation exposure was relatively low compared with other reported values of patient dose during chest radiography. The estimated effective dose for an average-size patient during chest radiography with posteroanterior and lateral projections is 0.085 mSv for the conventional and 0.14 mSv for the AMBER technique.     

A technique for computer-guided stereotaxis without preoperative head fixation

A CT-guided stereotactic method is described which uses a standard BRW frame for probe insertion but which does not require frame fixation to the skull during the localizing scan. The patient is instead scanned wearing three radiopaque scalp markers, and new software utilized to obtain BRW coordinates. Acceptable accuracy for targets greater than one centimeter in diameter was obtained in phantom trials and in three case reports. This technique may be helpful for stereotactic targets greater than one centimeter in diameter and when preoperative head fixation is not desirable or possible.     

利用3D打印颅脑辐射等效体模进行个性化适形放疗的剂量验证

目的 建立利用3D打印颅脑辐射等效体模对患者进行个性化放疗剂量验证的方法,为三维适形放射治疗安全提供一种可靠的剂量保证手段。方法 采集两例患者（患者1和患者2）的CT图像数据,基于患者1的图像数据,重建其颅骨与脑组织,制作颅脑体模,验证颅骨与脑组织的等效材料。基于患者2的图像数据,根据3D图像重建并选用组织等效材料重建完全的头颅结构,采用3D打印技术制作全头颅体模。通过对目标区域插入电离室剂量仪并行放射治疗方案,获得头颅体模病灶部的剂量,验证和校准实际放疗计划的安全性。结果 对所获两个体模分别进行DR、CT成像,颅脑体模的等效骨骼与患者1骨骼的X射线灰度值差异为13 721,颅脑体模的等效脑组织与患者1的脑组织的CT值差异为35~40 HU,全头颅体模等效颞肌与患者2的颞肌组织的CT值差异为18~28 HU,影像数据表明体模材质的辐射等效性与人体组织近似,并且等效剂量分布符合常规治疗范围,体模的剂量验证可以有效验证放疗计划系统的准确性。结论 基于3D打印和组织等效技术所设计的个性化放疗体模,可应用于个性化放射治疗验证。体模制作方法简单快速,个性化程度高,为三维适形放射治疗安全提供一种可靠的剂量保证手段。     

Contrast-detail phantom study for x-ray spectrum optimization regarding chest radiography using a cesium iodide-amorphous silicon flat-panel detector

RATIONALE AND OBJECTIVES: The purpose of this study evaluating a cesium iodide-amorphous silicon-based flat-panel detector was to optimize the x-ray spectrum for chest radiography combining excellent contrast-detail visibility with reduced patient exposure. MATERIALS AND METHODS: A Lucite plate with 36 drilled holes of varying diameter and depth was used as contrast-detail phantom. For 3 scatter body thicknesses (7.5 cm, 12.5 cm, 21.5 cm Lucite) images were obtained at 113 kVp, 117 kVp, and 125 kVp with additional copper filter of 0.2 and 0.3 mm, respectively. For each setting, radiographs acquired with 125 kVp and no copper filter were taken as standard of reference. On soft-copy displays, 3 observers blinded to the exposure technique evaluated the detectability of each aperture in each image according to a 5-point scale. The number of points given to all 36 holes per image was added. The scores of images acquired with filtration were compared with the standard images by means of a multivariate analysis of variance. Radiation burden was approximated by referring to the entrance dose and calculated using Monte Carlo method. RESULTS: All 6 evaluated x-ray spectra resulted in a statistically equivalent contrast-detail performance when compared with the standard of reference. The combination 125 kVp with 0.3 mm copper was most favorable in terms of dose reduction (approximately 33%). CONCLUSION: Within the constraints of the presented contrast-detail phantom study simulating chest radiography, the CsI/a-Si system enables an addition of up to 0.3 mm copper filtration without the need for compensatory reduction of the tube voltage for providing constant image quality. Beam filtration reduces radiation burden by about 33%.     

The effect of beam tube potential variation on gonad dose to patients during chest radiography investigated using high sensitivity LiF:Mg,Cu,P thermoluminescent dosemeters

Optimization of X-ray beam tube potential (kVp) in radiological examinations can minimize patient dose. This research aims to investigate the effect of tube potential variation on gonad doses to patients during posteroanterior (PA) chest radiography examinations. This study was carried out using a Toshiba general purpose X-ray unit and a Rando phantom. Dose measuring equipment included an ion chamber system, a dose-area product (DAP) meter and a thermoluminescent dosemeter (TLD) reader system with high sensitivity TLD pellets of LiF:Mg,Cu,P for low level gonad dose measurement. PA chest exposures of the phantom to produce a constant exit dose were made using a standard low tube potential (range 60-100 kVp) non-grid technique and a high tube potential (range 95-150 kVp) grid technique. Entrance surface doses (ESDs) and DAPs were also included in the measurements. Effective doses (EDs) were computed from ESD and DAP measurements using NRPB-SR262 and Xdose software. Results show that with the low tube potential technique both ovary dose and testes dose increase with increasing tube potential; statistically significant correlations of r = 0.994 (p = 0.0006) and r = 0.998 (p = 0.001), respectively, were found. For both organs, doses increase at a rate of approximately 2% per kVp. With the high tube potential technique there is insignificant correlation between gonad doses and tube potential. When comparing patient doses from typical exposures made at 70 kVp (low tube potential non-grid technique) with doses from exposures made at 120 kVp (high tube potential grid technique), the high tube potential technique delivers significantly higher values for ESD, and ovary, testes and effective doses by factors of 1.7, 5.2, 5.5 and 2.7, respectively.     

3D cerebral angiography: radiation dose comparison with digital subtraction angiography

BACKGROUND AND PURPOSE: As the use of 3D rotational angiography (3D RA) for the evaluation of cerebral vasculature becomes more widespread, it is important to evaluate this imaging method's effect on patient radiation dose. The purpose of the study is to measure 3D RA radiation dose as compared with biplanar digital subtraction angiography (DSA). METHODS: The distribution and peak skin dose were measured for 3D RA and biplanar DSA by using an anthropomorphic skull phantom. In addition, the cumulative incident dose, summed over all images in each acquisition, was determined. Measurements were acquired for our facility's standard 3D RA acquisition mode (25 degrees /s rotational speed; 162 total frames) and other available acquisition mode selections. RESULTS: For 3D RA, the skin dose was found to be distributed across the back and sides of the skull with the peak skin dose located at the center of the back of the skull. The peak skin dose for the standard 3D RA acquisition mode was 15 mGy. For a biplanar DSA run, the peak skin dose was 58 mGy, also located at the back of the skull. The cumulative incident dose for the standard 3D RA acquisition mode was 33 mGy, compared with 53 mGy for biplanar DSA. CONCLUSION: The patient radiation dose for 3D RA is significantly lower than for biplanar DSA, by nearly a factor of 4 in peak skin dose and 40% lower in cumulative incident dose.     

Dynamic digital subtraction evaluation of regional pulmonary ventilation with nonradioactive xenon

A method of evaluating pulmonary ventilation with a 57-cm image intensifier/television (II/TV) digital chest system is reported. With this method, the patient inhales a mixture of xenon and oxygen gases while dynamic imaging of the chest is done. Images of the airways and ventilated portions of the lungs are obtained by subtraction of images acquired before and after the xenon-oxygen mixture is administered. The feasibility of the method was evaluated by studies with xenon-filled tubes, an airway phantom, and a ventilation phantom. The results indicate that tubes larger than 3.2 mm in diameter are detectable at a xenon concentration of 41%, and that gas flow and flow distribution can be examined after image subtraction. If background subtraction is incomplete because of motion, the visibility of small airways is reduced greatly, although unventilated regions can still be delineated. The initial evaluation of this technique included imaging a healthy volunteer during xenon inhalation.     

Measurement of effective dose of the assisting person in diagnostic X-ray examination

We measured the effective dose received by the person assisting the patient at diagnostic X-ray examination. Measurement was done when a patient's chest, abdomen, lumbar vertebrae, hip joint, skull, cervical vertebrae, or knee joint was examined by radiography. A body phantom including human bones exposed to radiation was used in the role of the patient. Some exposure conditions for these measurements were the same as those used routinely in computed radiography. Effective dose was measured directly with an ionization survey meter. As a result, the effective dose of the person assisting with axial projection of the hip joint was 124 microSv, which was higher than that for other regions and projections. If the assisting person helped a patient without using any protective device, the effective dose would be low enough to ignore. However, because medical staff are frequently exposed to radiation, optimal protection is crucial to prevent unnecessary radiation.     

Variable compensation technique for digital radiography of the chest

The authors describe a new technique, variable compensation (VC) radiography, for digital radiography of the chest. It permits retrospective adjustment of image display while maintaining improved mediastinal signal-to-noise ratio (S/N) from aggressive x-ray equalization. A fraction of a logarithmic image representing the profile of the beam intensity incident on the patient is subtracted from a logarithmic equalized image. VC images of a chest phantom were generated with various weightings of the beam-profile image. Edge artifacts were substantially reduced with a weighting of greater than 0.5 and eliminated with a weighting of 1.0. The S/N properties of VC images were measured with a series of plastic squares placed over various regions of the chest phantom. The S/N of the squares in the dense sub-diaphragm were improved twofold compared with the S/N on unequalized radiographs, whereas the S/N in the lung was reduced by 30%. Studies of a volunteer revealed the ability to render images with aggressive equalization (for improved mediastinal visualization) and images with the appearance of traditional chest radiographs.     

Experimental assessment of the Advanced Collapsed-cone Engine for scalp brachytherapy treatments

PurposeTo experimentally assess the performance of the Advanced Collapsed-cone Engine (ACE) for ¹⁹²Ir high-dose-rate brachytherapy treatment planning of nonmelanoma skin cancers of the scalp.Methods and MaterialsA layered slab phantom was designed to model the head (skin, skull, and brain) and surface treatment mold using tissue equivalent materials. Six variations of the phantom were created by varying skin thickness, skull thickness, and size of air gap between the mold and skin. Treatment planning was initially performed using the Task Group 43 (TG-43) formalism with CT images of each phantom variation. Doses were recalculated using standard and high accuracy modes of ACE. The plans were delivered to Gafchromic EBT3 film placed between different layers of the phantom.ResultsDoses calculated by TG-43 and ACE and those measured by film agreed with each other at most locations within the phantoms. For a given phantom variation, average TG-43– and ACE-calculated doses were similar, with a maximum difference of (3 ± 12)% (k = 2). Compared to the film measurements, TG-43 and ACE overestimated the film-measured dose by (13 ± 12)% (k = 2) for one phantom variation below the skull layer.ConclusionsTG-43– and ACE-calculated and film-measured doses were found to agree above the skull layer of the phantom, which is where the tumor would be located in a clinical case. ACE appears to underestimate the attenuation through bone relative to that measured by film; however, the dose to bone is below tolerance levels for this treatment.     

Detection of ground-glass opacities by use of hybrid iterative reconstruction (iDose) and low-dose 256-section computed tomography: a phantom study

The detection of ground-glass opacities (GGOs) is an important issue in lung cancer screening with low-dose CT. The iterative reconstruction (IR) technique has the ability to improve the image quality relative to the filtered back projection (FBP) technique with low-dose CT. Our purpose was to investigate the ability to detect GGO in a chest phantom using a low-dose CT and hybrid IR, named iDose. Simulated GGOs in a chest phantom were scanned with 256-section CT at tube current second products of 20, 50, 100, and 200 mAs. Five radiologists visually assessed the detectability of GGOs in the phantom. The contrast-to-noise ratio (CNR) for GGOs was used as an estimate of image quality. Comparison of the detectability and CNR between standard images with 200 mAs-FBP and low-dose images with 20, 50, and 100-mAs FBP/iDose were performed by ANOVA with Dunnett’s and Tukey’s test. The detectability was significantly lower at 20-mAs FBP/iDose and 50-mAs FBP than that at 200-mAs FBP (p < 0.05). There was no significant difference between 50-mAs iDose and 200-mAs FBP and between 100-mAs iDose/FBP and 200-mAs FBP. The CNR was significantly higher on iDose images than that on FBP images at each mAs value. The CNR at 200-mAs FBP was the same as that at 50-mAs iDose (CNR:1.8). The hybrid IR technique and low-dose CT imaging with 50 mAs enabled noise and to maintain the detectability for GGOs in a chest phantom that is equivalent to the reference acquisitions of 200 mAs with FBP.     

Effect of kilovoltage on detectability of pulmonary nodules in a chest phantom.

A partial chest phantom was constructed to examine the effect of kilovoltage on the detectability of pulmonary nodules. Four different energies were studied: 100, 150, 200, and 300 kVp. Nodule detectability improved with increasing energies up to 200 kVp, but improvement was relatively small and was accompanied by an almost equal rise in the number of false positive readings. Patient exposures were least at 200 kVp. There seems to be no advantage in a 300 kVp technique, since nodule detectability decreased and patient exposures increased at this energy.     

A phantom for dose-image quality optimization in chest radiography

Optimization in chest radiography requires evaluation of patient dose and image quality. This study is aimed at proposing a simple geometrical phantom that realistically simulates the important anatomical regions of the thorax. For this purpose, the standard LucAl chest phantom is modified by adding an "anthropomorphic" insert and image quality test plate. Different test objects are arranged on the plate in three important anatomical areas; lung, cardiac, and subdiaphragmal regions. The aim is to simultaneously find two types of image quality index, objective and subjective, which can be used to compare different images in order to select the better image. Two objective indices are proposed, areal contrast index DeltaC(a) and scatter fraction P(s) and two subjectively estimated, a low contrast visualization index P(low) and a high contrast visualization index P(high). To demonstrate the potential of this phantom method it was applied to an X-ray unit to find the optical film density that ensures optimal visualization in different anatomical areas. It was found for the X-ray system under investigation that the automatic exposure control could be set to produce an optical density of about 1.8 in the lung field. The reported method is easily implemented in any clinical situation where optimization of chest radiography is needed.     

The use of a semi-customized phantom for verification of conformal plans.

We have developed a technique for inverse treatment planning of prostate therapy designed to improve the degree of conformation between the dose distribution and the target volume. We compared the inverse plan with a "standard" four-field box technique as well as a four-field technique using oblique fields ("cross technique"). We validated the dosimetry of the inverse plan using Fricke gel solution in phantom specifically designed for this purpose. The phantom is a Plexiglas tank with a cross section, which approximates the dimensions of the pelvis. Anatomical data from computed tomography (CT) images of a patient were used to simulate organs in our phantom. This allows us to calculate dose distributions with the external geometry of the phantom and internal anatomy of the patient. Dose-volume histograms (DVHs) for the three different plans were calculated. The phantom containing the Fricke gel was irradiated according to the inverse plan. Magnetic resonance (MR) images was used to determine the dose distribution delivered to the phantom. We observe, on DVHs, that the inverse plan significantly reduces the dose to the rectum and the bladder but slightly increases the inhomogeneity inside the target volume. Correlation is good between isodoses on MR images and calculated isodoses. We conclude that inverse planning software can greatly improve the conformal degree of treatment to the prostate. This technique could be applied to other complex anatomic sites at which dose to organs at risk is a limiting factor and increased dose to the target volume is indicated. Our phantom and the Fricke gel solution are convenient to carry out validation of conformal treatments.     

Effective dose in Albanian direct chest fluoroscopy

In the absence of reliable supplies of X-ray film, direct fluoroscopy is still extensively used in Albania, with chest radiology a particularly common application. This paper aims to quantify both patient skin dose and the risk-related quantity effective dose for direct fluoroscopy units based in seven different Albanian X-ray departments. A standard Quality Assurance (QA) protocol was used to assess tube potential accuracy, half value layer and X-ray tube output of these units. Three groups of X-ray beam parameters were defined from the QA results, covering the range of chest posteroanterior (PA) fluoroscopy technique factors seen during the study. Organ-equivalent doses were then measured for a nominal PA chest fluoroscopy examination using a Rando anthropomorphic phantom loaded with lithium fluoride thermoluminescent dosimeter chips. Normalised organ dose factors are listed for the three groups of beam conditions simulated. Using these factors, effective dose for the seven systems surveyed was found to be between 0.06 and 0.42 mSv for a 20 s PA chest fluoroscopy examination. Mean effective dose for this group of systems was 0.22 mSv which is a factor of 13 greater than mean effective dose for film/screen PA chest radiography in the UK, whereas entrance surface dose was a factor of 50 greater than the current EU reference level. Received: 11 February 2000 Accepted: 23 May 2000     

Development and characterisation of a head calibration phantom for in vivo measurements of actinides.

The investigation of actinides' internal contamination in human body makes use of a variety of techniques. In large scale screening the technique of "in vivo" evaluation of bone 241Am burden via the determination of the nuclide activity in the skull is often used. For this purpose, adequate calibration procedures and standard phantoms are needed. The present paper summarises the studies and technical procedures followed for the development of a calibration phantom based on a commercial Alderson angiographic head in which a set of 24 241Am point sources were embedded. A theoretical study was first carried out, at the ENEA Institute for Radiation Protection, using the MCNP4-B Monte Carlo code to determine the point source distribution that closely approximates a homogeneous bone contamination. The numerical models were also used to evaluate the resulting degree of approximation. The point sources were prepared at the ENEA National Metrology Institute for ionising radiation quantities and were traceable to the Italian national standard of radionuclide activity. The sources were prepared by quantitatively dispensing a liquid solution onto a plastic disc. The activity of each source was checked by gamma-ray spectrometry and the reproducibility of the activity values was determined. Each source was then placed in the optimum position in the skull, given by the Monte Carlo modelling, by a precision mechanical device. The phantom was finally used to calibrate a whole body counter operating at the ENEA Institute for Radiation Protection. The paper reports the main theoretical and experimental aspects of this work, and also discusses the results of the first calibrations.     

Phantom study of fusion image of CT and SPECT with body-contour generated from external Compton scatter sources

PURPOSE: A phantom study was conducted to evaluate the feasibility of body contour definition with Compton scatter photons from external sources of technetium-99m pertechnetate (Tc-99m) to create a fusion image of CT and SPECT images. METHODS: External sources of 1 mCi (37 MBq) Tc-99m were placed on each collimator, and body-contour SPECT images were obtained with an energy window of 100 keV +/- 25% for detecting 90 degrees and 180 degrees Compton scatter photons of Tc-99m from the body surface in water-filled cylindrical and hexagonal phantoms, and in a chest phantom with a Tc-99m-avid simulated lung nodule and multimethod surface markers. In the chest phantom, each transaxial SPECT slices was registered with the corresponding CT slice by using image-matching soft ware. A summation of the registered images yielded a three-dimensional (3-D) fusion image of this phantom. RESULTS: This method clearly visualized the body contour on all the SPECT slices in all the phantoms except for the complex hexagonal phantom. There was no significant difference between the known and SPECT-measured diameters of the cylindrical phantom. The fit of CT and SPECT images of the chest phantom was achieved with a mean alignment error of 5% in visual inspection, which was improved to 0.2% after correction of the magnification of the SPECT images according to the resultant dimensional differences. The 3-D fusion image of this phantom effectively visualized the anatomic location of the lung nodule and surface markers. CONCLUSION: This simple method effectively provided boundary information on the cold phantoms. Although further improvements in the registration technique with CT images are desirable, the body-contour SPECT image obtained by this method has the potential for accurately creating a 3-D fusion image with CT images, and is a feasible way of anticipating the anatomical localization of a target tissue.