X-ray scatter in projection radiography.

Projection radiography is the most common radiological modality, and radiation safety of it concerns both radiation workers and the public. We measured and generated a series of scattered radiation maps for projection radiography and estimated effective doses of the supporting person during exposure. Measured adult patient protocols included chest posterior-anterior, chest lateral, pelvis anterior-posterior (AP), abdomen AP and bedside chest AP. Maps concretise spatial distribution and the scattered radiation dose rates in different imaging protocols. Highest and lowest rates were measured in abdomen AP and bedside chest AP protocols, respectively. The effective dose of supporting person in abdomen AP examination at distance of 0.5 m was 300 nSv and in bedside supine chest AP examination at distance of 0.7 m was 0.5 nSv. The estimated annual effective dose of emergency unit radiographer was 0.11 mSv. The obtained effective dose values are small compared to annual dose limits of radiation workers and the public.

Relaxation anisotropy of quantitative MRI parameters in biological tissues.

Quantitative MR relaxation parameters vary in the sensitivity to the orientation of the tissue in the magnetic field. In this study, the orientation dependence of multiple relaxation parameters was assessed in various tissues. Ex vivo samples of each tissue type were prepared either from bovine knee (tendon, cartilage) or mouse (brain, spinal cord, heart, kidney), and imaged at 9.4 T MRI with T1, T2, continuous wave (CW-) T1ρ, adiabatic T1ρ and T2ρ, and Relaxation along fictitious field (RAFF2-4) sequences at five different orientations with respect to the main magnetic field. Relaxation anisotropy of the measured parameters was quantified and compared. The highly ordered collagenous tissues, i.e. cartilage and tendon, presented the highest relaxation anisotropy for T2, CW-T1ρ with spin-lock power < 1 kHz, Ad-T2ρ and RAFF2-4. Maximally anisotropy was 75% in cartilage and 30% in tendon. T1 and adiabatic T1ρ did not exhibit observable anisotropy. In the other measured tissue types, anisotropy was overall less than 10% for all the parameters. The results confirm that highly ordered collagenous tissues have properties that induce very clearly observable relaxation anisotropy, whereas in other tissues the effect is not as prominent. Quantitative comparison of anisotropy of different relaxation parameters highlights the importance of sequence choice and design in MR imaging.

Orientation anisotropy of quantitative MRI parameters in degenerated human articular cartilage.

Quantitative magnetic resonance (MR) relaxation parameters demonstrate varying sensitivity to the orientation of the ordered tissues in the magnetic field. In this study, the orientation dependence of multiple relaxation parameters was assessed in cadaveric human cartilage with varying degree of natural degeneration, and compared with biomechanical testing, histological scoring, and quantitative histology. Twelve patellar cartilage samples were imaged at 9.4 T MRI with multiple relaxation parameters, including T1 , T2 , CW - T1ρ , and adiabatic T1ρ , at three different orientations with respect to the main magnetic field. Anisotropy of the relaxation parameters was quantified, and the results were compared with the reference measurements and between samples of different histological Osteoarthritis Research Society International (OARSI) grades. T2 and CW - T1ρ at 400 Hz spin-lock demonstrated the clearest anisotropy patterns. Radial zone anisotropy for T2 was significantly higher for samples with OARSI grade 2 than for grade 4. The proteoglycan content (measured as optical density) correlated with the radial zone MRI orientation anisotropy for T2 (r = 0.818) and CW - T1ρ with 400 Hz spin-lock (r = 0.650). Orientation anisotropy of MRI parameters altered with progressing cartilage degeneration. This is associated with differences in the integrity of the collagen fiber network, but it also seems to be related to the proteoglycan content of the cartilage. Samples with advanced OA had great variation in all biomechanical and histological properties and exhibited more variation in MRI orientation anisotropy than the less degenerated samples. Understanding the background of relaxation anisotropy on a molecular level would help to develop new MRI contrasts and improve the application of previously established quantitative relaxation contrasts.

COMPARISON OF ORGAN-BASED TUBE CURRENT MODULATION AND BISMUTH SHIELDING IN CHEST CT: EFFECT ON THE IMAGE QUALITY AND THE PATIENT DOSE.

The aim of the study was to compare the absorbed doses and image quality of organ-based tube current modulation (OBTCM) and bismuth shielding of breasts and thyroid against regular tube current modulation in chest CT scan. An anthropomorphic phantom and MOSFET dosemeters were used to evaluate absorbed doses. Image quality was assessed from HU and noise. Relative to the reference scan, the average absorbed dose reduction with OBTCM was 5.2% and with bismuth shields 24.2%. Difference in HU values compared to the reference varied between -4.1 and 4.2 HU in OBTCM scan and between -22.2 and 118.6 HU with bismuth shields. Image noise levels varied between 10.0 to 26.3 HU in the reference scan, from 9.6 to 27.7 HU for the OBTCM scan and from 11.9 to 43.9 HU in the bismuth scan. The use of bismuth shields provided greatest dose reduction compared to the investigated OBTCM.

The repeatability of T2 relaxation time measurement of human knee articular cartilage.

OBJECTIVES: To assess short- and long-term repeatability of T2 relaxation time measurements of the knee articular cartilage. MATERIALS AND METHODS: The right knees of nine asymptomatic volunteers (age 30-38 years, five male, four female) were imaged at 1.5 T in three sessions 1 and 2 weeks apart. To observe short-term repeatability, the measurements were repeated three times within one of the three imaging sessions for each volunteer. T2 relaxation time was mapped using a multi-slice multi-echo spin echo sequence in axial and sagittal planes. Cartilage was manually segmented and repeatability, as measured by root-mean-square coefficient of variation (CVRMS) was evaluated both for the entire bulk cartilage of each joint surface in the slice and separately for each region of interest (ROI) at different topographical locations and separately for the superficial and deep half of each ROI. RESULTS: For bulk T2, the long-term repeatability was 3.2, 5.4, and 3.7%, and the short-term reproducibility was 3.9, 3.9, and 3.4% for bulk femoral, tibial, and patellar cartilage, respectively. There were no significant differences between long-term and short-term repeatability in superficial or deep cartilage when comparing CVRMS values (p = 0.338 and 0.700, respectively). For individual ROIs, the repeatability varied between 2.5 and 22.2% depending on the topographical location. CONCLUSION: The current results show mostly good repeatability. However, there were remarkable variations of T2 between bulk cartilage and different ROIs, bulk cartilage showing better repeatability. With careful patient positioning T2 can be accurately determined for different cartilage surfaces.