Hounsfield Values Research Articles

Pleomorphic adenoma of parotid gland: delayed enhancement on computed tomography

To assess the efficacy of multiphasic CT with 8 min delayed acquisition in the differential diagnosis between pleomorphic adenomas and other parotid neoplasias. Between January 2004 and April 2007, 62 patients with parotid enlargement were enrolled in this prospective study. The CT protocol applied included the following four acquisitions: without contrast medium and 30 s, 120 s and 8 min after intravenous injection of contrast medium. We considered the degree of the enhancement of the lesions (rated as "low", "moderate" and "strong") and the degree of enhancement homogeneity (rated as "not homogeneous", "mildly homogeneous" and "uniform"). These parameters were compared with Hounsfield values of the lesions computed in each phase. The diagnosis was confirmed in all patients after surgery. On histological examination, 36 tumours were classified as pleomorphic adenomas and 26 as non-pleomorphic adenomas. On the basis of a statistical comparison, the third phase proved to be the most effective in the differential diagnosis between pleomorphic adenoma and non-pleomorphic adenomas, both for the assessment of the degree of the enhancement (in this phase, strong enhancement showed a sensitivity of 61.11%, specificity of 100%, positive predictive value (PPV) of 100% and negative predictive value (NPV) of 53.33%) and, above all, for the homogeneity of the enhancement (in this phase, indeed, uniform enhancement showed sensitivity, specificity, PPV and NPV of 100%). Our results seem to indicate that multiphasic CT with 8 min delayed acquisition allows the differential diagnosis between pleomorphic adenomas and other parotid neoplasias.

Fatty liver and chronic inflammation in Chinese adults

Objective To investigate the significance of fatty liver as predictor of insulin resistance (IR) and chronic inflammation. Research design and methods This cross-sectional study included 450 adults of Han Chinese origin aged ≥35. Excluded were cases with hepatitis B or C, alcoholic liver disease, or currently using thiazolidinedione. The volunteers were screened for the presence of the components of metabolic syndrome (MtS). IR index was estimated by the homeostasis model assessment. The fatty liver index was evaluated by computed tomography, calculated as the liver/spleen (L/S) ratio arrived at by averaging Hounsfield values obtained for five 3-mm slices. Serum levels of adiponectin, C-reactive protein (CRP), leptin, interleukin-6 (IL-6) and tumor necrosis factor-α (TNF-α) were checked in 100 subjects with low-L/S ratio and 100 age- and sex-matched controls. Results Fatty liver index correlated with all MtS traits and IR index. The values of L/S ratios in subjects with 0, 1, 2, 3 and ≥4 traits of MtS were 1.25 ± 0.13, 1.18 ± 0.16, 1.12 ± 0.21, 1.05 ± 0.25 and 0.92 ± 0.25, respectively ( p < 0.001). In our stepwise regression analysis to compare the L/S ratios to the conventional traits of MtS for association with adipokine dysregulation, we found L/S ratio to be independently associated with most of them: adiponectin ( p < 0.001), CRP ( p < 0.001), IL-6 ( p = 0.005) and TNF-α ( p = 0.014). Conclusion In Chinese, fatty liver index correlated well with IR index and can be a better marker of chronic inflammation than the conventional components of MtS.

TU-FF-A4-03: A Three-Pass Method for Metal Artifact Reduction in Computed Tomography

Purpose: A method for the reduction of metal artifacts in computed tomography(CT)images is presented. Method and Materials: The method consists of three steps. In the first step, standard CTreconstruction is used to obtain an initial image containing metal artifacts. This image is segmented using k‐means clustering in order to obtain a binary metal‐background image. The metal is forward projected to mask the metal area in the sinogram data, and the metal shadow area is bridged using interpolation. A second image is reconstructed from this sinogram using standard backprojection. Then, the k‐means clustering is applied to the second reconstruction in order to identify four image regions: air, soft tissue (low), soft tissue (high), and bone. The Hounsfield value of each region is set to the mean of each region, except for the bone region where the original values are kept. We use this model image to create a metal shadow replacement by forward projection into the original sinogram. When inserting the model data into the sinogram, we make sure that the model area connects to the borders of the metal shadow. The final image is reconstructed from the sinogram in which metal line integrals are replaced by the model line integrals (third step). Results: Artifacts, e.g. from gold seeds in the breast or prostate, hip implants, or dental fillings can be significantly reduced. In cases of large implants, the method homogenizes image intensities in the surrounding soft tissues, which is helpful for the accurate planning of radiation therapy. Conclusions: The presented three‐pass metal artifact reduction method extends a recently published method by a linear interpolation step, which improves image quality, because more accurate model images can be derived for the replacement of the corrupted metal shadow in sinograms.

Er:YAG Laser Osteotomy Based on Refined Computer-Assisted Presurgical Planning: First Clinical Experience in Oral Surgery

This case report was aimed at primary clinical experience concerning surgical extraction of a displaced tooth with the help of the Er:YAG laser based on refined computer-assisted presurgical planning. The case refers to the extraction of a displaced maxillary canine in a female patient. For the osteotomy, a pulsed Er:YAG laser was applied with pulse energy of 500 mJ, pulse duration of 250 microsec and pulse frequency of 12 Hz. The fiber tip (1000 microm) was kept with a 1-2 mm distance to the bone surface. Refined presurgical computer-assisted planning was performed with regard to minimization of bone loss, especially for the sake of preservation of the alveolar ridge. Based on a detailed three-dimensional (3D) reconstruction of the patient's anatomy, dynamical simulations of a buccal and a palatinal variant of access osteotomy were provided. Additionally, a volumetric profile of bone tissue quality based on Hounsfield values was generated. By means of the 3D reconstruction and the tissue quality profile, both bone thickness and quality was evaluated as superior in the palatinal rather than in the vestibular part. Therefore, a classical buccal access window was chosen. The laser osteotomy allowed an exact cut geometry without any thermal damage and merely minimal bone loss. The enhanced possibilities by laser osteotomy allowed for full exploitation of presurgical planning. As regards the actual case, computer-assisted planning was of benefit for an appropriate choice of access osteotomy by enabling evaluation of the consistency of the bony structures.

In Vivo Characterization and Quantification of Atherosclerotic Carotid Plaque Components With Multidetector Computed Tomography and Histopathological Correlation

In a previous in vitro study we have demonstrated that atherosclerotic plaque components can be characterized with multidetector computed tomography (MDCT) based on differences in Hounsfield values (HV). Now we evaluated the use of MDCT in vivo to characterize and quantify atherosclerotic carotid plaque components compared with histology as reference standard. Fifteen symptomatic patients with carotid stenosis (>70%) underwent MDCT angiography before carotid endarterectomy (CEA). From each CEA specimen 3 histological sections and corresponding MDCT images were selected. The HV of the major plaque components were assessed. The measured HV were: 657+/-416HU, 88+/-18HU, and 25+/-19HU for calcifications, fibrous tissue, and lipid core, respectively. The cut-off value to differentiate lipid core from fibrous tissue and fibrous tissue from calcifications was based on these measurements and set at 60 HU and 130 HU, respectively. Regression plots showed good correlations (R2>0.73) between MDCT and histology except for lipid core areas, which had a good correlation (R2=0.77) only in mildly calcified (0% to 10%) plaques. MDCT is able to quantify total plaque area, calcifications, and fibrous tissue in atherosclerotic carotid plaques in good correlation with histology. Lipid core can only be adequately quantified in mildly calcified plaques.

Histologically verified bone wax (beeswax) granuloma after median sternotomy in 17 of 18 autopsy cases

To evaluate the sternum from ordinary or forensic autopsy cases with a midline sternal cutaneous scar macro- and microscopically and using computed tomography (CT) to detect if the haemostatic bone sealant bone wax (beeswax) had been applied after median sternotomy and if the bone wax had elicited inflammation. During a 3-year period, the sterna of 18 consecutive cadavers (15 ordinary autopsies, 3 forensic) who prior to death had undergone surgery with median sternotomy were examined macro- and microscopically and with CT. In addition, one virgin sternum was smeared with bone wax at the upper half after bench sternotomy, sutured and examined with CT. Unused bone wax was examined with CT for attenuation measurements. Macroscopically, bone wax was seen in 17 of 18 sterna. Acute inflammation was found in one, chronic inflammation and foreign body multinucleated giant cells were seen around the bone wax in 17 sterna. No inflammation was found in one. CT could only detect foci in the operated sterna with attenuation values from -45 to +20 Hounsfield units (HU) and values about -80 HU were found in the virgin sternum. Unused bone wax measured about -100 HU. Bone wax is non-resorbable and induces chronic inflammation in the operated sternum up to 10 years after application. Measurement of Hounsfield units with CT of the operated sterna could not verify bone wax granuloma.

Structural and radiological parameters for the characterization of jawbone

The aim of this study was to determine the Hounsfield values of selected bone sites on a computed tomography (CT) scan of the jaw and to investigate the relationship between this radiological parameter and structural parameters. A selection of 24 bone samples out of eight cadaver human jaws was made. The following parameters were measured: Hounsfield value in the jaw (HU1) determined by a first CT scan, Hounsfield value of the excised bone specimen (HU2) by a second CT scan, bone mineral density (BMD) by a dual-energy X-ray absorptiometry scan, bone volume (BV/TV) by the microfocus CT scan, first peak transmission time (T(US-1)) and first zero crossing transmission time (T(US-2)) by an ultrasound measurement and Young's modulus (E(MECH)) by a compression test. Thirteen specimens were composed of a mix of trabecular and a small amount of cortical bone, while another 11 specimens were composed of trabecular bone only. A good correlation was found between the HU value of the specimen (HU2) and BMD (rho = 0.99), BV/TV (rho = 0.97), T(US-1) (rho = -0.83), T(US-2) (rho = -0.87) and E(MECH) (rho = 0.83). For the pure trabecular bone specimens, the HU value of the excised bone specimen (HU2) was highly correlated (rho = 0.95) with the HU value of the total jaw scan (HU1). For mixed trabecular-cortical bone specimens, this relationship was weak (rho = 0.57). With the current CT scan technology, predictions of the mechanical properties of trabecular jaw bone based on Hounsfield values were only valid for jaws with a thin layer of cortical bone. For jaws with a thicker cortical layer, the prediction of the mechanical properties decreased significantly.

Orbital Neurofibroma Presenting with a Negative Hounsfield Unit on Computerized Tomography

Purpose: To report a case of diffuse orbital neurofibroma which displayed an unusual computed tomography (CT) feature. Methods: Results of ocular examination, orbital CT examination and pathological findings in a patient with a space-occupying orbital lesion are presented. Results: Orbital CT evaluation of a male patient, aged one and a half years old, revealed a right orbital lesion with a strongly negative value in Hounsfield units. The preoperative diagnosis was a dermoid cyst. An anterior orbitotomy was performed, and the surgical specimen demonstrated a typical plexiform neurofibroma with routine hematoxylin and eosin staining and immunohistochemical studies. Conclusions: Plexiform orbital neurofibromas may demonstrate a negative Hounsfield value on CT examination.

Reduction of motion blurring artifacts using respiratory gated CT in sinogram space: A quantitative evaluation

Techniques have been developed for reducing motion blurring artifacts by using respiratory gated computed tomography (CT) in sinogram space and quantitatively evaluating the artifact reduction. A synthetic sinogram was built from multiple scans intercepting a respiratory gating window. A gated CT image was then reconstructed using the filtered back-projection algorithm. Wedge phantoms, developed for quantifying the motion artifact reduction, were scanned while being moved using a computer-controlled linear stage. The resulting artifacts appeared between the high and low density regions as an apparent feature with a Hounsfield value that was the average of the two regions. A CT profile through these regions was fit using two error functions, each modeling the partial-volume averaging characteristics for the unmoving phantom. The motion artifact was quantified by determining the apparent distance between the two functions. The blurring artifact had a linear relationship with both the speed and the tangent of the wedge angles. When gating was employed, the blurring artifact was reduced systematically at the air-phantom interface. The gated image of phantoms moving at 20 mm/s showed similar blurring artifacts as the nongated image of phantoms moving at 10 mm/s. Nine patients were also scanned using the synchronized respiratory motion technique. Image artifacts were evaluated in the diaphragm, where high contrast interfaces intercepted the imaging plane. For patients, this respiratory gating technique reduced the blurring artifacts by 9%-41% at the lung-diaphragm interface.

In vitro characterization of atherosclerotic carotid plaque with multidetector computed tomography and histopathological correlation

This in vitro study evaluated the performance of 16-slice multidetector computed tomography (MDCT) in the assessment of carotid plaque components, with histology as the gold standard. Twenty-one specimens (n=21) were scanned and reconstructed after optimization of the protocol. Three corresponding MDCT images and histologic sections were selected from each specimen. The Hounsfield values (HV) of the major plaque components (calcifications, fibrous tissue and lipid) were assessed. Plaque areas (mm2) assessed with MDCT were compared with the results from histologic analysis. A value of 140 kVp and an intermediate reconstruction algorithm was the optimal protocol. In 15 out of 21 specimens it was possible to match MDCT images with histology. The HV of calcifications, fibrous tissue and lipid were 45+/-21, 79+/-20 and 960+/-491 HU (P<0.001), respectively. Plaque areas were compared in 27 matched levels. The calcified and lipid areas on MDCT and histology correlate well (R2=0.83 and R2=0.68, respectively). The mean difference in lipid area was 0.1 mm2 (95% CI=-2.1-2.3 mm2). This in vitro study showed that MDCT is capable of characterizing and quantifying the lipid rich portion of the atherosclerotic plaque.

Quantitation of the reconstruction quality of a four‐dimensional computed tomography process for lung cancer patients

We have developed a four-dimensional computed tomography (4D CT) technique for mapping breathing motion in radiotherapy treatment planning. A multislice CT scanner (1.5 mm slices) operated in ciné mode was used to acquire 12 contiguous slices in each couch position for 15 consecutive scans (0.5 s rotation, 0.25 s between scans) while the patient underwent simultaneous quantitative spirometry measurements to provide a sorting metric. The spirometry-sorted scans were used to reconstruct a 4D data set. A critical factor for 4D CT is quantifying the reconstructed data set quality which we measure by correlating the metric used relative to internal-object motion. For this study, the internal air content within the lung was used as a surrogate for internal motion measurements. Thresholding and image morphological operations were applied to delineate the air-containing tissues (lungs, trachea) from each CT slice. The Hounsfield values were converted to the internal air content (V). The relationship between the air content and spirometer-measured tidal volume (v) was found to be quite linear throughout the lungs and was used to estimate the overall accuracy and precision of tidal volume-sorted 4D CT. Inspection of the CT-scan air content as a function of tidal volume showed excellent correlations (typically r>0.99) throughout the lung volume. Because of the discovered linear relationship, the ratio of internal air content to tidal volume was indicative of the fraction of air change in each couch position. Theoretically, due to air density differences within the lung and in room, the sum of these ratios would equal 1.11. For 12 patients, the mean value was 1.08 +/- 0.06, indicating the high quality of spirometry-based image sorting. The residual of a first-order fit between v and V was used to estimate the process precision. For all patients, the precision was better than 8%, with a mean value of 5.1% +/- 1.9%. This quantitative analysis highlights the value of using spirometry as the metric in sorting CT scans. The 4D reconstruction provides the CT data required to measure the three-dimensional trajectory of tumor and lung tissue during free breathing.

Low-contrast detectability in volume rendering: a phantom study on multidetector-row spiral CT data.

To cope with the increasing amount of CT data, there is growing interest in direct volume-rendering techniques (VRT) as a diagnostic tool. The aim of this phantom study was to analyze the low-contrast detectability (LCD) of VRT compared with multi-planar reformations (MPR). Soft tissue lesions were simulated by spheres of different diameters (3-8 mm). The average lesion density was 15 HU compared with a background density of 35 HU. Two different CT protocols with 40 and 150 mAs were performed on a multi-detector row CT. The scanning parameters were as following: 140 kV; 2x0.5-mm slice collimation; pitch 2 (table movement per rotation/single slice collimation), and reconstruction with 0.5-mm slice thickness at 0.5-mm interval. A B30 kernel was used for reconstruction. The VRT was performed by mapping Hounsfield values to gray levels equal to a CT window (center: 60 HU; window: 370 HU ). A linear ramp was applied for the opacity transfer function varying the maximum opacity between 0.1 and 1.0. A statistical method based on the Rose model was used to calculate the detection threshold depending on lesion size and image noise. Additionally, clinical data of 2 patients with three liver lesions of different sizes and density were evaluated. In VRT, LCD was most dependent on object size. Regarding lesions larger than 5 mm, VRT is significantly superior to MPR (p<0.05) for all opacity settings. In lesions sized 3-5 mm a maximum opacity level approximately 40-50% showed a near equivalent detectability in VRT and MPR. For higher opacity levels VRT was superior to MPR. Only for 3-mm lesions MPR performed slightly better in low-contrast detectability (p<0.05). Compared with MPR, VRT shows similar performance in LCD. Due to noise suppression effects, it is suited for visualization of data with high noise content.

318 poster The selection of Hounsfield value (HF) in TPS for inhomogeneity corrections on electron beams

318 poster The selection of Hounsfield value (HF) in TPS for inhomogeneity corrections on electron beams

On visual determination of full inspiration on CT images.

The aim of this study was to evaluate the ability of experienced thoracic radiologists to assess full inspiration based on two CT slices, one above and one below the carina, in normal subjects. Ten healthy volunteers were studied. Total lung capacity (TLC) was measured with a body plethysmograph. High-resolution computed tomography (HRCT) was performed in two slices at TLC and at various expired volumes. Mean Hounsfield values (HU) were calculated. Unidentifiable images, stored on a web server, were analysed visually by experienced thoracic radiologists. The results show that the mean lung density at TLC varied by approximately 40 HU between individuals. Within an individual this may correspond to a decrease in lung volume of approximately 25% of TLC. On visual determination of images taken at 65-74% of TLC, more than one-third of the images were assessed as taken at full inspiration; of the images taken at 75-84% of TLC, approximately 50% were assessed as taken at full inspiration. We conclude that visual determination of full inspiration on CT images in normal subjects is highly inaccurate. If quantitative density measurements are to be used in the diagnosis or follow-up of lung disease, thorough control of full inspiration is recommended.

Computer-aided diagnosis in contrast-enhanced CT colonography: an approach based on contrast.

Automation in colorectal mass detection is achieved as soon as the voxels representing colorectal masses can be automatically segmented. We tested the Hounsfield (HU) value in intensely contrast enhanced high-resolution CT colonography for automated segmentation of colorectal masses in 18 patients with 35 polyps (28 < 10 mm, 7 > or = 10 mm) and 7 carcinomas. Mean HU values of the colonic wall and masses were determined to deduce a gradient threshold for a segmentation process, which encodes the voxels bordering the colonic lumen with a colour ranging in intensity from 0 to 100% according to the selected gradient threshold range in the volume rendering. The results of the automated segmentation process were superimposed on a virtual double contrast and endoscopic display and validated through correlation with morphology. Mean HU values and their standard deviations for the colonic wall, polyps < 10 mm, polyps > or = 10 mm and carcinomas were 63 +/- 24, 154 +/- 38, 116 +/- 41 and 108+/-29 HU, respectively. A gradient threshold ranging from 90 to 160 HU resulted in colour pools in 6 of 7 of polyps > or = 10 mm, and 6 of 7 carcinomas that were significant enough to prospectively guide the reader's attention to these masses. Due to the superposition of "false-positive" voxels in the projection view, the virtual endoscopic perspective was superior to the virtual double contrast display for controlling the segmentation results. The HU value is promising for automated segmentation of colorectal masses but needs to be combined with morphological parameters to render automated colorectal mass detection more accurate. Further refinements of the method with subsequent analysis of its accuracy, as well as analogue studies with contrast-enhanced MRI, appear warranted. More information at http://www.multiorganscreening.org

Spiral computed tomographic imaging related to computerized ultrasonographic images of carotid plaque morphology and histology.

Echolucency of carotid atherosclerotic plaques, as evaluated by computerized B-mode ultrasonographic images, has been associated with an increased incidence of brain infarcts on cerebral computed tomographic scans. We tested the hypotheses that characterization of carotid plaques on spiral computed tomographic images correlates with that on computerized B-mode ultrasonographic images and that spiral computed tomographic imaging predicts the histomorphometric plaque content. The study included 38 patients with neurologic symptoms and at least 50% stenosis of the ipsilateral carotid artery. High-resolution B-mode ultrasonographic images and spiral computed tomographic images of carotid plaques were computer processed to yield a quantitative measure, the gray scale level of the plaque. The mean Hounsfield value for spiral computed tomographic images correlated with the gray scale median for B-mode ultrasonographic images (univariate linear regression analysis: r = 0.45; P = .01) and the histologic content of calcification in the plaque (r = 0.34; P = .04) but not with lipid, hemorrhage, or fibrous tissue in the plaque. Spiral computed tomographic imaging seems to correlate with B-mode ultrasonographic imaging for showing plaque characteristics. Spiral computed tomographic attenuation was also correlated with the amount of calcification noted on histologic examination but not with lipid and hemorrhage, the components thought to characterize vulnerable, rupture-prone plaques.

Relation between carbon ion ranges and x-ray CT numbers.

Measurements of carbon ion ranges in various phantom materials and real bones are presented. Together with measured Hounsfield values, an empirical relation between ranges and Hounsfield units is derived, which is an important prerequisite for treatment planning in carbon ion therapy.

Evaluation des Elektronendichte-Phantoms CIRS Model 62

The properties of the electron density phantom CIRS M62 were studied. Physical and electron densities were calculated for all tissue substitutes, and compared to the values given in the data sheet and to the recommendations of the ICRU Report 44. The phantom was scanned in standard-CT and spiral-CT mode with different acquisition parameters. Especially manufactured tissue substitutes for dense bone were analysed for artifacts. Hounsfield values of all tissues substitutes were determined with the treatment planning system CadPlan®. Calibration curves were calculated and compared to a stoichiometric calibration for real tissue. There was good agreement between the values calculated and the values given by the manufacturer. The tissue substitutes were only approximately tissue equivalent. The tissue substitutes for dense bone showed small artifacts. The calculated calibration curves were in good agreement with the stoichiometric calibration curve.

Determination of the Hounsfield value for CT-based design of custom femoral stems

Ct and advanced computer-aided design techniques offer the means for designing customised femoral stems. Our aim was to determine the Hounsfield (HU) value of the bone at the corticocancellous interface, as part of the criteria for the design algorithm. We obtained transverse CT images from eight human cadaver femora. The proximal femoral canal was rasped until contact with dense cortical bone was achieved. The femora were cut into several sections corresponding to the slice positions of the CT images. After obtaining a computerised image of the anatomical sections using a scanner, the inner cortical contour was outlined and transferred to the corresponding CT image. The pixels beneath this contour represent the CT density of the bone remaining after surgical rasping. Contours were generated automatically at nine HU levels from 300 to 1100 and the mean distance between the transferred contour and each of the HU-generated contours was computed. The contour generated along the 600-HU pixels was closest to the inner cortical contour of the rasped femur and therefore 600 HU seem to be the CT density of the corticocancellous interface in the proximal part of cadaver femora. Generally, femoral bone with a CT density beyond 600 HU is not removable by conventional reamers. Thus, we recommend the 600 HU threshold as one of several criteria for the design of custom femoral implants from CT data.

Nondestructive Testing Method for Finding out the Defects in a Composite Liner

A composite liner of carbon phenolic has been inspected by ultrasonic, X-ray radiography andX-ray computed tomography (CT) to find defects like delaminations, debonds, voids, foreign inclusions, etc.The geometry, detection of multiple defects and porosity of the liner make ultrasonic testing (pulse-echo anddrycoupling) difficult for inspection. X-ray radiography being a non-contact technique finds multiple defectsbut compresses the structural information of 3-D volume into a 2-D image and interferes with overlyingand underlying areas of the object. X-ray CT generates an image of a thin and cross-sectional slice ofan object. R e linear attenuation coefficients in terms of Hounsfield values have been measured, comparedand correlated with CT images at the contrasts observed. 3-D images can be generated by stacking2-D cross-sectional images of the slices. These 3-D images can be cut at any angle of choice for mappingthe extent of delaminated/debonded areas. This type of information is difficult to obtain with conventionalnon-destructive testing techniques.