High CT Number Research Articles

Evaluation of imaging performance of major image guidance systems.

Purpose:The imaging characteristics of two popular kV cone-beam CT (CBCT) and two MVCT systems utilised in image-guided radiation therapy (IGRT) were evaluated.Materials and methods:The study was performed on Varian Clinac iX, Elekta Synergy S, Siemens Oncor, and Tomotherapy. A CT phantom (Catphan-504, Phantom Laboratory, Salem, NY) was scanned for measurements of image quality including image noise, uniformity, density accuracy, spatial resolution, contrast linearity, and contrast resolution. The measurement results were analysed using in-house image analysis software. Reproducibility, position correction, and geometric accuracy were also evaluated with markers in a smaller alignment phantom. The performance evaluation compared volumetric image properties from these four systems with those from a conventional diagnostic CT (CCT).Results:It was shown that the linearity of the two kV CBCT was fairly consistent with CCT. The Elekta CBCT with half-circle 27-cm FOV had higher CT numbers than the other three systems. The image noises of the Elekta kV CBCT, Siemens MV CBCT, and Tomotherapy fan-beam CT (FBCT) are about 2–4 times higher than that of the Varian CBCT. The spatial resolutions of two kV CBCTs and two MV CBCTs were 8-11 lp/cm and 3-5 lp/cm, respectively.Conclusion:Elekta CBCT provided a faster image reconstruction and low dose per scan for half-circle scanning. Varian CBCT had relatively lower image noise. Tomotherapy FBCT had the best uniformity.

Dose to water versus dose to medium in proton beam therapy

Dose in radiation therapy is traditionally reported as the water-equivalent dose, or dose to water. Monte Carlo dose calculations report dose to medium and thus a methodology is needed to convert dose to medium into dose to water (or vice versa) for comparison of Monte Carlo results with results from planning systems. This paper describes the development of a formalism to convert dose to medium into dose to water for proton fields when simulating the dose with Monte Carlo techniques. The conversion is based on relative stopping power but also considers energy transferred via nuclear interactions. The influence of different interaction mechanisms of proton beams (electromagnetic versus nuclear) is demonstrated. Further, an approximate method for converting doses retroactively is presented. Based on the outlined formalism, five proton therapy patients with a total of 33 fields were analyzed. Dose distributions, dose volume histograms and absolute doses to assess the clinical significance of differences between dose to medium and dose to water are presented. We found that the difference between the two dose reporting definitions can be up to 10% for high CT numbers if analyzing the mean dose to the target. The difference is clinically insignificant for soft tissues. For the structures analyzed, the mean dose to water could be converted to dose to medium by applying a correction factor increasing linearly with increasing average CT number in the volume. We determined that an approximate conversion method, done retroactively with an energy-independent stopping power ratio and without considering nuclear interaction events separately (as compared to on-the-fly conversion during simulation), is sufficiently accurate to compute mean doses. It is insufficient, however, when analyzing the beam range. For proton beams stopping in bony anatomy, the predicted beam range can differ by 2–3 mm when comparing dose to tissue and dose to water.

SU‐FF‐T‐405: Dose to Water Versus Dose to Medium in Proton Beam Therapy

Purpose: Dose in radiation therapy is traditionally reported as dose‐to‐water, Dw. Monte Carlo (MC) dose calculations report dose‐to‐medium, Dm. A methodology is needed to convert Dm into Dw for comparing MC and planning system results. This work addressed the following questions for proton therapy: What formalism allows the conversion from Dm to Dw?1. Can we convert MC calculated Dm into Dw retroactively or do we have to convert during particle tracking?2. What is the difference between Dm and Dw when analyzing patient data in terms of dose distributions, dose volume histograms and absolute doses?3. Is there a difference in the predicted beam range between Dm and Dw?Method: We did develop a formalism to convert Dm into Dw for proton beam dose calculations. Three different methods are introduced, an approximate method based on relative stopping power which allows retroactive conversion, a method considering energy dependent relative stopping powers, and a method incorporating nuclear interaction events as well. A total of 33 patient fields were analyzed. MC calculated dose distributions, dose volume histograms and absolute doses to assess the clinical significance of differences between Dm and Dw were compared. Results: We found that the difference between the three conversion methods was within 1% in most cases when analyzing mean doses to contoured structures. Further, we found that the difference between Dm and Dw can be up to 10% for high CT numbers. The difference is clinically insignificant for soft tissues. For proton beams stopping in bony anatomy, the predicted beam range can differ by 2–3 mm when comparing Dm and Dw. Conclusion: For comparison between MC and analytical dose distributions in proton therapy, a dose conversion is required. However, retroactive conversion seems to be sufficiently accurate in most cases, except for the end of range.

SU‐GG‐I‐28: Performance Comparison of Two Different Cone‐Beam CT Systems

Purpose: To evaluate and compare the imaging performance of two popular cone‐beam CT (CBCT) systems used for image‐guided radiation therapy. Method and Materials: The study was carried out on Varian Clinac iX equipped with OBI/CBCT and Elekta Synergy equipped with XVI/CBCT. The performance evaluation involved comparison of volumetric image data taken from two systems. Two CT phantoms (Catphan‐504 and 600, Phantom Laboratory, Salem, NY) were scanned using the Varian CBCT with standard half and full fan setup, and Catphan‐600 was also scanned on Elekta CBCT with half and full circle scans at different resolutions and field‐of‐view (FOV). In‐house image analysis software was used to measure the mean CT numbers, standard deviations, and image noise for 5×5 mm ROI in seven different density materials. Image quality, reproducibility, position correction, and geometric accuracy were also evaluated with markers in a small alignment phantom. The image quality measurements included uniformity, linearity, image resolution, density accuracy, and image noise. Results: The linearity for both phantoms was fairly consistent using the Varian CBCT. The Elekta CBCT with half circle 27×27 FOV had higher CT numbers as compared to its other three modes. With the same phantom for low‐density materials, the CT numbers with Varian CBCT were 300–600 units lower than those with Elekta CBCT. The image noise of full and half circle 27×27 FOV were about 5 and 2 times, respectively, higher than for the Varian CBCT, while the image noise levels in its other modes were similar. The accuracy of the image systems was comparable. Conclusion: This study confirmed the comparability of imaging performance of both systems. While the Elekta CBCT provided timely image reconstruction, relatively higher image noise was observed. Our objective evaluation of imaging performance demonstrated that the volumetric data rendered from both CBCT systems is accurate as compared with conventional CT.

SU‐GG‐I‐11: Dose and Image Quality Evaluation of a Mobile CT Scanner for Head and Neck Imaging

Purpose: To evaluate the radiation dose delivered to patients and personnel by a mobile x‐ray CT scanner designed for bedside imaging of the head and neck, and to examine image quality under clinical conditions. Method and Materials: Computed Tomography Dose Index (CTDI) was measured using a 100 mm pencil ionization chamber and 16 cm diameter acrylic phantom over a range of acquisition parameters on a mobile CT scanner (Neurologica Ceretom, Danvers, MA). Scatter radiation was measured using the same phantom. Image quality was evaluated using the manufacturer's QA phantom and the common CATPHAN phantom. Results: At 120 kVp, CTDI‐100 measured 44.8, 83.5, and 122 mGy at 7 mA and 2, 4, and 6 seconds per rotation, respectively. At 140 kVp, commonly used for head scanning, the CTDI‐100 measured 65.3, 126.8, and 176.3 mGy at 7 mA and 2, 4, and 6 seconds per rotation, respectively. All measured doses were within 10% of the CTDI values indicated to the operator on the scanner's console. Using protective lead curtains provided with the scanner, scatter radiation was well within ALARA standards. CATPHAN images demonstrated acceptable alignment, slice width and incrementation accuracy, geometric accuracy, low contrast resolution, high contrast spatial resolution, image uniformity and CT number linearity at clinical techniques. Conclusion: When operated in “low dose” (2 seconds/rotation) mode, the radiation dose delivered by the mobile CT scanner is below or comparable to the ACR's diagnostic Reference Value (RV) for head CT dose. The “standard” (4 seconds/rotation) and “high‐quality” (6 seconds/rotation) modes deliver more radiation, with a corresponding increase in image quality. Assessment using an industry‐standard phantom produced acceptable image quality performance under clinical conditions. With proper precautions, the scanner can be safely used in most intensive care environments without additional shielding, with minimal occupational exposure.

In-Vivo Relation between CT Attenuation Value and Shockwave Fragmentation

To use CT attenuation numbers as a means of determining the susceptibility of an artificial stone to in-vivo fragmentation with extracorporeal shockwave lithotripsy (SWL). Four types of artificial kidney stones having different CT attenuation values were used. One randomly selected stone was implanted in the renal pelvis of a kidney of 12 young pigs and exposed in vivo to 2500 shockwaves (21 kV) using an electrohydraulic lithotripter. Bilateral nephrectomy was performed after SWL. Fragments were strained through a mesh with a 3.1-mm grid, and the debris left on the mesh was dried and weighed. Fragmentation coefficients (FCs) were associated with CT attenuation values using a statistical model. The relation between FC and CT number was significant, indicating that as CT attenuation increases, FC is reduced. Larger stone fragments were obtained from stones with higher CT numbers. Initial stone weight was not a significant explanation for variations in FC. The CT values could be helpful in selecting patients for SWL in the future. However, other parameters such as stone porosity, shape, and roughness also will have to be considered.

Accuracy of the CT numbers of simulated lung nodules imaged with multi-detector CT scanners

A study was performed to determine the accuracies and reproducibilities of the CT numbers of simulated lung nodules imaged with multi-detector CT scanners. The nodules were simulated by spherical balls of three diameters (4.8, 9.5, and 16 mm) and two compositions (50 and 100 mg/cc CaCO3 in water-equivalent plastic). All were scanned in a liquid-water-filled container at the center of a water-equivalent-plastic phantom and in air cavities within the same phantom using GE multi-detector CT scanners. The nodules were also scanned within simulated lung regions in an anthropomorphic thorax section phantom that was bolused on both sides with water-equivalent slabs. Results were compared for three scanning protocols--the protocol for the National Lung Screening Trial (NLST), the protocol for the Lung Tissue Research Consortium (LTRC) study, and a high resolution (small pitch, thin slice and small scan interval) higher dose "gold standard" protocol. Scans were repeated three times with each protocol to assess reproducibility. The CT numbers of the nodules in water were found to be nearly independent of nodule size. However, the presence and the size of an air cavity surrounding a nodule had a significant effect (e.g., the CT number of a 50 mg/cc nodule was 64 HU in water, 37 HU in a 1.8 cm diameter air cavity, and 19 HU in a 4.4 cm diameter air cavity). This variability of CT number with size of air cavity may affect the results of the LTRC study in which patients are scanned at both full inspiration and full expiration. The CT numbers of the 9.5 and 16 mm diameter nodules within the anthropomorphic phantom were highly reproducible (average standard deviations of 2 HU or less) for all protocols. On the other hand, both accuracy and reproducibility were significantly degraded for the 4.8 mm diameter nodules, especially for the NLST (2.5 mm thickness, 2 mm slice interval) technique. Use of thinner slice (1.25 mm) and slice interval (1.25 mm) scans that can be reconstructed retrospectively from the multi-detector helical CT projection data of the standard NLST protocol yield CT numbers for the 4.8 mm diameter nodules that are more accurate and reproducible than those of the standard NLST technique. In general, the CT numbers of the nodules were found to be lower at positions near the centers of the lungs and near the spine, which is probably due to increased beam hardening in those regions. Also, larger nodules were found to have higher CT numbers than smaller nodules, consistent with results obtained on early single slice GE CT scanners. Until manufacturers develop quantitative CT scanners with improved x-ray beam hardening and scatter corrections, it is recommended that reference phantoms be employed to more accurately assess the calcium contents of patient lung nodules in screening and tissue characterization studies and in eventual computer-aided detection and diagnosis applications.

TH‐C‐ValB‐06: Thoracic Proton Treatment Planning Strategies Based On the 4D CT Information

Purpose: Particularly in the case of thoracic radiation therapy, there are substantial inter‐ and intra‐fractional variations in shape, volume and position of treatment targets and the intervening and surrounding normal tissues. The purpose of this work is to develop proton treatment planning strategies for mobile tumors with and without mobile intervening structures based on 4D CT, and to assess the planning strategies using 4D CT data and daily in‐room CT information. Method and Materials: Five treatment planning strategies were evaluated based on (1) free breathing CT with small smearing, (2) free breathing CT with large smearing, (3) average CT with small smearing, (4) average CT with CT numbers inside the tumor volume replaced by higher CT numbers, and (5) maximum intensity projection CT. For a lung patient with large, 1.6 cm, tumor motion and immobile surrounding tissues, treatment plans were designed using strategies 1, 2 and 4. Each treatment plan was recalculated on five daily CT images using bony structure alignment. For an esophagus patient with 3.5 cm tumor motion and large cardiac, liver and spleen motion, treatment plans were designed using strategies 1, 2, 3 and 5. Each treatment plan was recalculated in all 10 phases of the 4D CT. Results: For the lung patient, the tumor coverage evaluated using the five daily CT's is superior when using strategies 2 and 4 as compared to strategy 1. However, the lung sparing is superior using strategy 4 compared to strategy 2. For the esophagus patient, the treatment plans using strategy 2 and 5 covered the targets for each 4D CT phase while the plan using strategy 1 and 3 caused significant under‐dosing. Conclusion: With the strategies developed using 4D CT data, good tumor coverage was achieved for the thoracic patients with large tumor and surrounding tissue motion using proton therapy.

A Retroperitoneal Bronchogenic Cyst Treated With Laparoscopic Surgery

No AccessJournal of UrologyClinical Urology: Case Report1 Feb 1997A Retroperitoneal Bronchogenic Cyst Treated With Laparoscopic Surgery Noriaki Tokuda, Seiji Naito, Jiro Uozumi, Hideo Shimura, Ryoichi Takayanagi, and Joichi Kumazawa Noriaki TokudaNoriaki Tokuda More articles by this author , Seiji NaitoSeiji Naito More articles by this author , Jiro UozumiJiro Uozumi More articles by this author , Hideo ShimuraHideo Shimura More articles by this author , Ryoichi TakayanagiRyoichi Takayanagi More articles by this author , and Joichi KumazawaJoichi Kumazawa More articles by this author View All Author Informationhttps://doi.org/10.1016/S0022-5347(01)65220-0AboutFull TextPDF ToolsAdd to favoritesDownload CitationsTrack CitationsPermissionsReprints ShareFacebookLinked InTwitterEmail "A Retroperitoneal Bronchogenic Cyst Treated With Laparoscopic Surgery." The Journal of Urology, 157(2), p. 619 References 1 : Retroperitoneal bronchogenic cyst presenting as an adrenal mass. Arch. Path. Lab. Med.1991; 115: 1057. Google Scholar 2 : Pseudoadrenal mass: unusual presentation of bronchogenic cyst. J. Ped. Surg.1991; 26: 1401. Google Scholar 3 : Infradiaphragmatic bronchogenic cyst with high CT numbers in a boy with primitive neuroectodermal tumor. Ped. Rad.1994; 24: 504. Google Scholar Department of Urology, First Department of Surgery and Third Department of Internal Medicine, Faculty of Medicine, Kyushu University, Fukuoka, Japan.© 1997 by American Urological Association, Inc.FiguresReferencesRelatedDetailsCited byISHIKAWA T, KAWABATA G, OKADA H, ARAKAWA S, KAMIDONO S and FUJISAWA M (2018) Retroperitoneal Bronchogenic Cyst Managed With Retroperitoneoscopic SurgeryJournal of Urology, VOL. 169, NO. 3, (1078-1079), Online publication date: 1-Mar-2003. Volume 157Issue 2February 1997Page: 619 Advertisement Copyright & Permissions© 1997 by American Urological Association, Inc.MetricsAuthor Information Noriaki Tokuda More articles by this author Seiji Naito More articles by this author Jiro Uozumi More articles by this author Hideo Shimura More articles by this author Ryoichi Takayanagi More articles by this author Joichi Kumazawa More articles by this author Expand All Advertisement PDF downloadLoading ...

Squamous cell carcinoma of the lung with high CT number, but without calcification

Squamous cell carcinoma of the lung with high CT number, but without calcification

Case Report: Misdiagnosis of an atypical pericardial cyst presenting in a patient with chest trauma

We report a patient who presented following major trauma to the chest who had a pericardial cyst in the anterior aspect of the upper mediastinum, the high CT number of which led to a misdiagnosis. The patient underwent surgery when the pericardial cyst was excised.

Pulmonary adenoid cystic carcinoma with calcification manifesting high CT-number mass report of a case

Pulmonary adenoid cystic carcinoma with calcification manifesting high CT-number mass report of a case

Bronchogenic cysts with high CT numbers: D. S. Mendelson, J. S. Rose, S. C. Efremidis, et al. Am J Roentgenol 140:463–465, (March), 1983

Bronchogenic cysts with high CT numbers: D. S. Mendelson, J. S. Rose, S. C. Efremidis, et al. Am J Roentgenol 140:463–465, (March), 1983

CT-number variability in thoracic geometry.

The use of absolute CT numbers for in vivo tissue characterization is compromised by a number of technical and geometrical factors. A phantom simulating thoracic geometry and containing intrapulmonary "features" was scanned on three CT scanners allowing for assessment of CT-number variations with a wide number of scanning and geometric parameters. It was found that, with thoracic geometry, the absolute CT numbers of intrapulmonary features (e.g., solitary pulmonary nodules) can vary significantly due to a number of CT scanning parameters, such as geometry, CT scanner used, and/or time. Such variations must be taken into account when establishing criteria for characterizing tissue types using CT numbers. However, results show that variations in quantitative behavior with reasonable changes in patient geometry do not preclude meaningful characterization of solitary lung nodules (using CT-number averages) using CT scans for the three CT scanners studied, providing CT-number threshold data are derived from the same model scanner and operating conditions. The use of CT-number patterns within high-density intrapulmonary pathology (e.g., solitary pulmonary nodules) is compromised by the fact that high CT-number patterns were found to be a function of the reconstruction filter used and object size as well as being influenced by details of the surrounding medium.

Bronchogenic cysts with high CT numbers.

Four patients with mediastinal masses are described. CT examinations demonstrated masses of high attenuation, and solid masses were suspected. At thoracotomy each patient had a cystic mass containing a brownish, turbid, mucoid material. The pathologic diagnosis in each case was a bronchogenic cyst. The possibility of such a cyst should not be excluded because of a high CT number, which reflects the turbid contents of the cyst.

CT DENSITOMETRY OF PULMONARY NODULES

Siegelman et al (AJR 135:1, 1980) could distinguish a high percentage of benign pulmonary nodules from malignant nodules by the high CT number of benign nodules. Others have found CT densitometry of nodules less reliable. Scanning lung nodules is technically difficult because of their small size and the large difference in density between them and the surrounding aerated lung. In order to test the reliability of CT number determinations under these conditions, we scanned a phantom containing plastic spheres of different sizes (1”, 1/2”, 1/4”) and densities, simulating soft tissue nodules surrounded by aerated lung. We used both 5-mm and 1.5-mm collimation. We found that the centering of the sphere in the scan plane is the most important variable determining the number of usable voxels for densitometry. If a 1/2” (12.5 mm) sphere is precisely centered in the scan plane, even 5-mm collimation affords a large number of usable voxels. With progressive decentering of the sphere, the fall-off in number of usable voxels is much faster for 5-mm than 1.5-mm collimation. Neither collimator gave a sufficient number of usable voxels for the 1/4” (6 mm) spheres, except for the densest sphere (Teflon, CT number 830). A computer model incorporating the scanning conditions gave an excellent match with the experimental data. We conclude that partial volume effects–the result of the interaction of the edge of the sphere with the 3-dimensional array of voxels–are the most important factors determining the number of usable voxels. With narrow collimation, decentering of the sphere in the scan plane is less important than with wider collimation. With extremely high density, even 1/4” (6 mm) spheres can be scanned with narrow collimation.

CALCIUM QUANTIFICATION IN PULMONARY NODULES USING DUAL ENERGY CT

The differentiation of benignity from malignancy in the patient presenting with a pulmonary nodule is a common clinical problem. Previous investigators using specialized single-energy scanning techniques have attempted this distinction based on the mean CT number of the nodule. The presence of high CT numbers in some benign nodules is presumably related to radiographically inapparent calcium in the nodule. Significant problems, and inaccuracies in the absolute value of CT numbers exists for commercial CT scanners, especially in the lung where beam hardening corrections are not optimal. A direct measurement of the calcium content of pulmonary nodules can be done with dual-energy CT. The differential absorption of high Z-number material when scanned at two different energies enables accurate determination of the amount of this material when present in small quantities. We have initiated a project to quantify the calcium content of pulmonary nodules in patients. Scans both with 5 mm and 1.5 mm collimation are obtained at 120 and 80 KvP. A calibration phantom containing known calciumequivalent solution is scanned with the patient to standardize CT numbers for each slice. Initial results in about ten patients indicates that calcium within pulmonary nodules can be quantified with CT. The range of measured mineral is between 0 and 500 mg/cm3. Dual energy scans may overcome the problems inherent in CT scanning at a single energy level.

Difference between liver and spleen CT numbers in the normal adult: its usefulness in predicting the presence of diffuse liver disease.

A constant relationship was found between the mean CT numbers of the liver and spleen in 100 normal adults. This relationship was characterized by a mean CT number consistently higher for the liver (24.9 +/- 4.6) than for the spleen (21.1 +/- 4.1). The range for liver CT numbers was 16.7-37.2, and for the spleen it was 14.9-34.3. The mean liver-spleen CT number difference for all subjects was 3.8 +/- 2.1 (p < 0.001); in every instance, the livers exhibiting the high mean CT numbers were in subjects with high mean spleen CT numbers, with the same concordance for low mean CT numbers. This relationship between liver and spleen may be useful in the clinical setting in which a normal liver with low CT numbers must be differentiated from one in which the CT number is low because of fatty infiltration; the fatty liver will exhibit a lower mean CT number than the spleen.