Musculoskeletal applications of flat-panel volume CT

Flat-panel volume computed tomography (fpVCT) is a recent development in imaging. We discuss some of the musculoskeletal applications of a high-resolution flat-panel CT scanner. FpVCT has four main advantages over conventional multidetector computed tomography (MDCT): high-resolution imaging; volumetric coverage; dynamic imaging; omni-scanning. The overall effective dose of fpVCT is comparable to that of MDCT scanning. Although current fpVCT technology has higher spatial resolution, its contrast resolution is slightly lower than that of MDCT (5-10HU vs. 1-3HU respectively). We discuss the efficacy and potential utility of fpVCT in various applications related to musculoskeletal radiology and review some novel applications for pediatric bones, soft tissues, tumor perfusion, and imaging of tissue-engineered bone growth. We further discuss high-resolution CT and omni-scanning (combines fluoroscopic and tomographic imaging).

Adaptive statistical iterative reconstruction reduces patient radiation dose in neuroradiology CT studies.

INTRODUCTION: Adaptive statistical iterative reconstruction (ASIR) can decrease image noise, thereby generating CT images of comparable diagnostic quality with less radiation. The purpose of this study is to quantify the effect of systematic use of ASIR versus filtered back projection (FBP) for neuroradiology CT protocols on patients' radiation dose and image quality. METHODS: We evaluated the effect of ASIR on six types of neuroradiologic CT studies: adult and pediatric unenhanced head CT, adult cervical spine CT, adult cervical and intracranial CT angiography, adult soft tissue neck CT with contrast, and adult lumbar spine CT. For each type of CT study, two groups of 100 consecutive studies were retrospectively reviewed: 100 studies performed with FBP and 100 studies performed with ASIR/FBP blending factor of 40 %/60 % with appropriate noise indices. The weighted volume CT dose index (CTDIvol), dose-length product (DLP) and noise were recorded. Each study was also reviewed for image quality by two reviewers. Continuous and categorical variables were compared by t test and free permutation test, respectively. RESULTS: For adult unenhanced brain CT, CT cervical myelography, cervical and intracranial CT angiography and lumbar spine CT both CTDIvol and DLP were lowered by up to 10.9 % (p < 0.001), 17.9 % (p = 0.005), 20.9 % (p < 0.001), and 21.7 % (p = 0.001), respectively, by using ASIR compared with FBP alone. Image quality and noise were similar for both FBP and ASIR. CONCLUSION: We recommend routine use of iterative reconstruction for neuroradiology CT examinations because this approach affords a significant dose reduction while preserving image quality.

CT radiation dose in children: a survey to establish age-based diagnostic reference levels in Switzerland

This work aimed at assessing the doses delivered in Switzerland to paediatric patients during computed tomography (CT) examinations of the brain, chest and abdomen, and at establishing diagnostic reference levels (DRLs) for various age groups. Forms were sent to the ten centres performing CT on children, addressing the demographics, the indication and the scanning parameters: number of series, kilovoltage, tube current, rotation time, reconstruction slice thickness and pitch, volume CT dose index (CTDI(vol)) and dose length product (DLP). Per age group, the proposed DRLs for brain, chest and abdomen are, respectively, in terms of CTDI(vol): 20, 30, 40, 60 mGy; 5, 8, 10, 12 mGy; 7, 9, 13, 16 mGy; and in terms of DLP: 270, 420, 560, 1,000 mGy cm; 110, 200, 220, 460 mGy cm; 130, 300, 380, 500 mGy cm. An optimisation process should be initiated to reduce the spread in dose recorded in this study. A major element of this process should be the use of DRLs.

Thoracoabdominal-aortoiliac multidetector-row CT angiography at 80 and 100 kVp: assessment of image quality and radiation dose

OBJECTIVE: To compare image quality and radiation dose of thoracoabdominal computed tomography (CT) angiography at 80 and 100 kVp and to assess the feasibility of reducing contrast medium volume from 60 to 45 mL at 80 kVp. MATERIALS AND METHODS: This retrospective study had institutional review board approval; informed consent was waived. Seventy-five patients who had undergone thoracoabdominal 64-section multidetector-row CT angiography were divided into 3 groups of 25 patients each. Patients of groups A (tube voltage, 100 kVp) and B (tube voltage, 80 kVp) received 60 mL of contrast medium at 4 mL/s. Patients of group C (tube voltage, 80 kVp) received 45 mL of contrast medium at 3 mL/s. Mean aortoiliac attenuation, image noise, and contrast-to-noise ratio were assessed. The measurement of radiation dose was based on the volume CT dose index. Three independent readers assessed the diagnostic image quality. RESULTS: Mean aortoiliac attenuation for group B (621.1 +/- 90.5 HU) was significantly greater than for groups A and C (485.2 +/- 110.5 HU and 483.1 +/- 119.8 HU; respectively) (P < 0.001). Mean image noise was significantly higher for groups B and C than for group A (P < 0.05). The contrast-to-noise ratio did not significantly differ between the groups (group A, 35.0 +/- 13.8; group B, 31.7 +/- 10.1; group C, 27.3 +/- 11.5; P = 0.08). Mean volume CT dose index in groups B and C (5.2 +/- 0.4 mGy and 4.9 +/- 0.3 mGy, respectively) were reduced by 23.5% and 27.9%, respectively, compared with group A (6.8 +/- 0.8 mGy) (P < 0.001). The average overall diagnostic image quality for the 3 groups was graded as good or better. The score for group A was significantly higher than that for group C (P < 0.01), no difference was seen between group A and B (P = 0.92). CONCLUSIONS: Reduction of tube voltage from 100 to 80 kVp for thoracoabdominal CT angiography significantly reduces radiation dose without compromising image quality. Reduction of contrast medium volume to 45 mL at 80 kVp resulted in lower but still diagnostically acceptable image quality.

Dose Reduction in Standard Head CT: First Results from a New Scanner Using Iterative Reconstruction and a New Detector Type in Comparison with Two Previous Generations of Multi-slice CT

PURPOSE Computed tomography (CT) accounts for more than half of the total radiation exposure from medical procedures, which makes dose reduction in CT an effective means of reducing radiation exposure. We analysed the dose reduction that can be achieved with a new CT scanner [Somatom Edge (E)] that incorporates new developments in hardware (detector) and software (iterative reconstruction). METHODS We compared weighted volume CT dose index (CTDIvol) and dose length product (DLP) values of 25 consecutive patients studied with non-enhanced standard brain CT with the new scanner and with two previous models each, a 64-slice 64-row multi-detector CT (MDCT) scanner with 64 rows (S64) and a 16-slice 16-row MDCT scanner with 16 rows (S16). We analysed signal-to-noise and contrast-to-noise ratios in images from the three scanners and performed a quality rating by three neuroradiologists to analyse whether dose reduction techniques still yield sufficient diagnostic quality. RESULTS CTDIVol of scanner E was 41.5 and 36.4 % less than the values of scanners S16 and S64, respectively; the DLP values were 40 and 38.3 % less. All differences were statistically significant (p < 0.0001). Signal-to-noise and contrast-to-noise ratios were best in S64; these differences also reached statistical significance. Image analysis, however, showed "non-inferiority" of scanner E regarding image quality. CONCLUSIONS The first experience with the new scanner shows that new dose reduction techniques allow for up to 40 % dose reduction while still maintaining image quality at a diagnostically usable level.

MDCT arthrography of the hip: value of the adaptive statistical iterative reconstruction technique and potential for radiation dose reduction.

OBJECTIVE: The purpose of this article is to assess the effect of the adaptive statistical iterative reconstruction (ASIR) technique on image quality in hip MDCT arthrography and to evaluate its potential for reducing radiation dose. SUBJECTS AND METHODS: Thirty-seven patients examined with hip MDCT arthrography were prospectively randomized into three different protocols: one with a regular dose (volume CT dose index [CTDIvol], 38.4 mGy) and two with a reduced dose (CTDIvol, 24.6 or 15.4 mGy). Images were reconstructed using filtered back projection (FBP) and four increasing percentages of ASIR (30%, 50%, 70%, and 90%). Image noise and contrast-to-noise ratio (CNR) were measured. Two musculoskeletal radiologists independently evaluated several anatomic structures and image quality parameters using a 4-point scale. They also jointly assessed acetabular labrum tears and articular cartilage lesions. RESULTS: With decreasing radiation dose level, image noise statistically significantly increased (p=0.0009) and CNR statistically significantly decreased (p=0.001). We also found a statistically significant reduction in noise (p=0.0001) and increase in CNR (p≤0.003) with increasing percentage of ASIR; in addition, we noted statistically significant increases in image quality scores for the labrum and cartilage, subchondral bone, overall diagnostic quality (up to 50% ASIR), and subjective noise (p≤0.04), and statistically significant reductions for the trabecular bone and muscles (p≤0.03). Regardless of the radiation dose level, there were no statistically significant differences in the detection and characterization of labral tears (n=24; p=1) and cartilage lesions (n=40; p≥0.89) depending on the ASIR percentage. CONCLUSION: The use of up to 50% ASIR in hip MDCT arthrography helps to reduce radiation dose by approximately 35-60%, while maintaining diagnostic image quality comparable to that of a regular-dose protocol using FBP.

Predicting dysthyroid optic neuropathy using computed tomography volumetric analyses of orbital structures

OBJECTIVE: To evaluate the ability of orbital apex crowding volume measurements calculated with multidetector-computed tomography to detect dysthyroid optic neuropathy. METHODS: Ninety-three patients with Graves' orbitopathy were studied prospectively. All of the patients underwent a complete neuro-ophthalmic examination and computed tomography scanning. Volumetric measurements were calculated from axial and coronal contiguous sections using a dedicated workstation. Orbital fat and muscle volume were estimated on the basis of their attenuation values (in Hounsfield units) using measurements from the anterior orbital rim to the optic foramen. Two indexes of orbital muscle crowding were calculated: i) the volumetric crowding index, which is the ratio between soft tissue (mainly extraocular muscles) and orbital fat volume and is based on axial scans of the entire orbit; and ii) the volumetric orbital apex crowding index, which is the ratio between the extraocular muscles and orbital fat volume and is based on coronal scans of the orbital apex. Two groups of orbits (with and without dysthyroid optic neuropathy) were compared. RESULTS: One hundred and two orbits of 61 patients with Graves' orbitopathy met the inclusion criteria and were analyzed. Forty-one orbits were diagnosed with Graves' orbitopathy, and 61 orbits did not have optic neuropathy. The two groups of orbits differed significantly with regard to both of the volumetric indexes (p<0.001). Although both indexes had good discrimination ability, the volumetric orbital apex crowding index yielded the best results with 92% sensitivity, 86% specificity, 81%/94% positive/negative predictive value and 88% accuracy at a cutoff of 4.14. CONCLUSION: This study found that the orbital volumetric crowding index was a more effective predictor of dysthyroid optic neuropathy than previously described computed tomography indexes were.

Effect of X-ray tube parameters, iodine concentration, and patient size on image quality in pulmonary computed tomography angiography: a chest-phantom-study

OBJECTIVES: The aim of this phantom study was to evaluate the contrast-to-noise ratio (CNR) in pulmonary computed tomography (CT)-angiography for 300 and 400 mg iodine/mL contrast media using variable x-ray tube parameters and patient sizes. We also analyzed the possible strategies of dose reduction in patients with different sizes. MATERIALS AND METHODS: The segmental pulmonary arteries were simulated by plastic tubes filled with 1:30 diluted solutions of 300 and 400 mg iodine/mL contrast media in a chest phantom mimicking thick, intermediate, and thin patients. Volume scanning was done with a CT scanner at 80, 100, 120, and 140 kVp. Tube current-time products (mAs) varied between 50 and 120% of the optimal value given by the built-in automatic dose optimization protocol. Attenuation values and CNR for both contrast media were evaluated and compared with the volume CT dose index (CTDI(vol)). Figure of merit, calculated as CNR/CTDIvol, was used to quantify image quality improvement per exposure risk to the patient. RESULTS: Attenuation of iodinated contrast media increased both with decreasing tube voltage and patient size. A CTDIvol reduction by 44% was achieved in the thin phantom with the use of 80 instead of 140 kVp without deterioration of CNR. Figure of merit correlated with kVp in the thin phantom (r = -0.897 to -0.999; P < 0.05) but not in the intermediate and thick phantoms (P = 0.09-0.71), reflecting a decreasing benefit of tube voltage reduction on image quality as the thickness of the phantom increased. Compared with the 300 mg iodine/mL concentration, the same CNR for 400 mg iodine/mL contrast medium was achieved at a lower CTDIvol by 18 to 40%, depending on phantom size and applied tube voltage. CONCLUSIONS: Low kVp protocols for pulmonary embolism are potentially advantageous especially in thin and, to a lesser extent, in intermediate patients. Thin patients profit from low voltage protocols preserving a good CNR at a lower exposure. The use of 80 kVp in obese patients may be problematic because of the limitation of the tube current available, reduced CNR, and high skin dose. The high CNR of the 400 mg iodine/mL contrast medium together with lower tube energy and/or current can be used for exposure reduction.

Dual energy versus single energy MDCT: measurement of radiation dose using adult abdominal imaging protocols

RATIONALE AND OBJECTIVES: The aim of this study was to measure the radiation dose of dual-energy and single-energy multidetector computed tomographic (CT) imaging using adult liver, renal, and aortic imaging protocols. MATERIALS AND METHODS: Dual-energy CT (DECT) imaging was performed on a conventional 64-detector CT scanner using a software upgrade (Volume Dual Energy) at tube voltages of 140 and 80 kVp (with tube currents of 385 and 675 mA, respectively), with a 0.8-second gantry revolution time in axial mode. Parameters for single-energy CT (SECT) imaging were a tube voltage of 140 kVp, a tube current of 385 mA, a 0.5-second gantry revolution time, helical mode, and pitch of 1.375:1. The volume CT dose index (CTDI(vol)) value displayed on the console for each scan was recorded. Organ doses were measured using metal oxide semiconductor field-effect transistor technology. Effective dose was calculated as the sum of 20 organ doses multiplied by a weighting factor found in International Commission on Radiological Protection Publication 60. Radiation dose saving with virtual noncontrast imaging reconstruction was also determined. RESULTS: The CTDI(vol) values were 49.4 mGy for DECT imaging and 16.2 mGy for SECT imaging. Effective dose ranged from 22.5 to 36.4 mSv for DECT imaging and from 9.4 to 13.8 mSv for SECT imaging. Virtual noncontrast imaging reconstruction reduced the total effective dose of multiphase DECT imaging by 19% to 28%. CONCLUSION: Using the current Volume Dual Energy software, radiation doses with DECT imaging were higher than those with SECT imaging. Substantial radiation dose savings are possible with DECT imaging if virtual noncontrast imaging reconstruction replaces precontrast imaging.

Radiation Dose to the Lens of the Eye from Computed Tomography Scans of the Head

While it is well known that exposure to radiation can result in cataract formation, questions still remain about the presence of a dose threshold in radiation cataractogenesis. Since the exposure history from diagnostic CT exams is well documented in a patient’s medical record, the population of patients chronically exposed to radiation from head CT exams may be an interesting area to explore for further research in this area. However, there are some challenges in estimating lens dose from head CT exams. An accurate lens dosimetry model would have to account for differences in imaging protocols, differences in head size, and the use of any dose reduction methods.

The overall objective of this dissertation was to develop a comprehensive method to estimate radiation dose to the lens of the eye for patients receiving CT scans of the head. This research is comprised of a physics component, in which a lens dosimetry model was derived for head CT, and a clinical component, which involved the application of that dosimetry model to patient data.

The physics component includes experiments related to the physical measurement of the radiation dose to the lens by various types of dosimeters placed within anthropomorphic phantoms. These dosimeters include high-sensitivity MOSFETs, TLDs, and radiochromic film. The six anthropomorphic phantoms used in these experiments range in age from newborn to adult.

First, the lens dose from five clinically relevant head CT protocols was measured in the anthropomorphic phantoms with MOSFET dosimeters on two state-of-the-art CT scanners. The volume CT dose index (CTDIvol), which is a standard CT output index, was compared to the measured lens doses. Phantom age-specific CTDIvol-to-lens dose conversion factors were derived using linear regression analysis. Since head size can vary among individuals of the same age, a method was derived to estimate the CTDIvol-to-lens dose conversion factor using the effective head diameter. These conversion factors were derived for each scanner individually, but also were derived with the combined data from the two scanners as a means to investigate the feasibility of a scanner-independent method. Using the scanner-independent method to derive the CTDIvol-to-lens dose conversion factor from the effective head diameter, most of the fitted lens dose values fell within 10-15% of the measured values from the phantom study, suggesting that this is a fairly accurate method of estimating lens dose from the CTDIvol with knowledge of the patient’s head size.

Second, the dose reduction potential of organ-based tube current modulation (OB-TCM) and its effect on the CTDIvol-to-lens dose estimation method was investigated. The lens dose was measured with MOSFET dosimeters placed within the same six anthropomorphic phantoms. The phantoms were scanned with the five clinical head CT protocols with OB-TCM enabled on the one scanner model at our institution equipped with this software. The average decrease in lens dose with OB-TCM ranged from 13.5 to 26.0%. Using the size-specific method to derive the CTDIvol-to-lens dose conversion factor from the effective head diameter for protocols with OB-TCM, the majority of the fitted lens dose values fell within 15-18% of the measured values from the phantom study.

Third, the effect of gantry angulation on lens dose was investigated by measuring the lens dose with TLDs placed within the six anthropomorphic phantoms. The 2-dimensional spatial distribution of dose within the areas of the phantoms containing the orbit was measured with radiochromic film. A method was derived to determine the CTDIvol-to-lens dose conversion factor based upon distance from the primary beam scan range to the lens. The average dose to the lens region decreased substantially for almost all the phantoms (ranging from 67 to 92%) when the orbit was exposed to scattered radiation compared to the primary beam. The effectiveness of this method to reduce lens dose is highly dependent upon the shape and size of the head, which influences whether or not the angled scan range coverage can include the entire brain volume and still avoid the orbit.

The clinical component of this dissertation involved performing retrospective patient studies in the pediatric and adult populations, and reconstructing the lens doses from head CT examinations with the methods derived in the physics component. The cumulative lens doses in the patients selected for the retrospective study ranged from 40 to 1020 mGy in the pediatric group, and 53 to 2900 mGy in the adult group.

This dissertation represents a comprehensive approach to lens of the eye dosimetry in CT imaging of the head. The collected data and derived formulas can be used in future studies on radiation-induced cataracts from repeated CT imaging of the head. Additionally, it can be used in the areas of personalized patient dose management, and protocol optimization and clinician training.

Volumetric quantification of atherosclerotic plaque in CT considering partial volume effect.

Coronary artery calcification (CAC) is quantified based on a computed tomography (CT) scan image. A calcified region is identified. Modified expectation maximization (MEM) of a statistical model for the calcified and background material is used to estimate the partial calcium content of the voxels. The algorithm limits the region over which MEM is performed. By using MEM, the statistical properties of the model are iteratively updated based on the calculated resultant calcium distribution from the previous iteration. The estimated statistical properties are used to generate a map of the partial calcium content in the calcified region. The volume of calcium in the calcified region is determined based on the map. The experimental results on a cardiac phantom, scanned 90 times using 15 different protocols, demonstrate that the proposed method is less sensitive to partial volume effect and noise, with average error of 9.5% (standard deviation (SD) of 5-7mm(3)) compared with 67% (SD of 3-20mm(3)) for conventional techniques. The high reproducibility of the proposed method for 35 patients, scanned twice using the same protocol at a minimum interval of 10 min, shows that the method provides 2-3 times lower interscan variation than conventional techniques.

Nontraumatic subarachnoid hemorrhage management: evaluation with reduced iodine volume at CT angiography.

PURPOSE: To evaluate the technical quality and the diagnostic performance of a protocol with use of low volumes of contrast medium (25 mL) at 64-detector spiral computed tomography (CT) in the diagnosis and management of adult, nontraumatic subarachnoid hemorrhage (SAH). MATERIALS AND METHODS: This study was performed outside the United States and was approved by the institutional review board. Intracranial CT angiography was performed in 73 consecutive patients with nontraumatic SAH diagnosed at nonenhanced CT. Image quality was evaluated by two observers using two criteria: degree of arterial enhancement and venous contamination. The two independent readers evaluated diagnostic performance (lesion detection and correct therapeutic decision-making process) by using rotational angiographic findings as the standard of reference. Sensitivity, specificity, and positive and negative predictive values were calculated for patients who underwent CT angiography and three-dimensional rotational angiography. The intraclass correlation coefficient was calculated to assess interobserver concordance concerning aneurysm measurements and therapeutic management. RESULTS: All aneurysms were detected, either ruptured or unruptured. Arterial opacification was excellent in 62 cases (85%), and venous contamination was absent or minor in 61 cases (84%). In 95% of cases, CT angiographic findings allowed optimal therapeutic management. The intraclass correlation coefficient ranged between 0.93 and 0.95, indicating excellent interobserver agreement. CONCLUSION: With only 25 mL of iodinated contrast medium focused on the arterial phase, 64-detector CT angiography allowed satisfactory diagnostic and therapeutic management of nontraumatic SAH.

Prognostic value of baseline total metabolic tumor volume (TMTV0) measured on FDG-PET/CT in patients with peripheral T-cell lymphoma (PTCL).

BACKGROUND: Most peripheral T-cell lymphoma (PTCL) patients have a poor outcome and the identification of prognostic factors at diagnosis is needed. PATIENTS AND METHODS: The prognostic impact of total metabolic tumor volume (TMTV0), measured on baseline [(18)F]2-fluoro-2-deoxy-d-glucose positron emission tomography/computed tomography, was evaluated in a retrospective study including 108 PTCL patients (27 PTCL not otherwise specified, 43 angioimmunoblastic T-cell lymphomas and 38 anaplastic large-cell lymphomas). All received anthracycline-based chemotherapy. TMTV0 was computed with the 41% maximum standardized uptake value threshold method and an optimal cut-off point for binary outcomes was determined and compared with others prognostic factors. RESULTS: With a median follow-up of 23 months, 2-year progression-free survival (PFS) was 49% and 2-year overall survival (OS) was 67%. High TMTV0 was significantly associated with a worse prognosis. At 2 years, PFS was 26% in patients with a high TMTV0 (>230 cm(3), n = 53) versus 71% for those with a low TMTV0, [P < 0.0001, hazard ratio (HR) = 4], whereas OS was 50% versus 80%, respectively, (P = 0.0005, HR = 3.1). In multivariate analysis, TMTV0 was the only significant independent parameter for both PFS and OS. TMTV0, combined with PIT, discriminated even better than TMTV0 alone, patients with an adverse outcome (TMTV0 >230 cm(3) and PIT >1, n = 33,) from those with good prognosis (TMTV0 ≤230 cm(3) and PIT ≤1, n = 40): 19% versus 73% 2-year PFS (P < 0.0001) and 43% versus 81% 2-year OS, respectively (P = 0.0002). Thirty-one patients (other TMTV0-PIT combinations) had an intermediate outcome, 50% 2-year PFS and 68% 2-year OS. CONCLUSION: TMTV0 appears as an independent predictor of PTCL outcome. Combined with PIT, it could identify different risk categories at diagnosis and warrants further validation as a prognostic marker.

3-D volume rendering maxillofacial analysis of angular measurements by multislice CT

Objective. This study was designed to determine the precision and accuracy of angular measurements using three-dimensional computed tomography (3D-CT) volume rendering by computer systems. Study design. The study population consisted of 28 dried skulls that were scanned with a 64-row multislice CT, and 3D-CT images were generated. Angular measurements, (n = 6) based upon conventional craniometric anatomical landmarks (n = 9), were identified independently in 3D-CT images by 2 radiologists, twice each, and were then performed by 3D-CT imaging. Subsequently, physical measurements were made by a third examiner using a Beyond Crysta-C9168 series 900 device. Results. The results demonstrated no statistically significant difference between interexaminer and intraexaminer analysis. The mean difference between the physical and 3-D-based angular measurements was -1.18% and -0.89%, respectively, for both examiners, demonstrating high accuracy. Conclusion. Maxillofacial analysis of angular measurements using 3D-CT volume rendering by 64-row multislice CT is established and can be used for orthodontic and dentofacial orthopedic applications.