Geometric accuracy in three-dimensional coordinates of Leksell stereotactic skull frame with wide-bore 1.5-T MRI compared with conventional 1.5-T MRI.

The use of 1.5-tesla (T) magnetic resonance (MR) imaging with a wide and simultaneously short bore enhances patient comfort compared with traditional 1.5-T MR imaging and is becoming increasingly available in stereotactic radiosurgery treatment planning. However, the geometric accuracy seems unavoidably worse in wide-bore MR imaging than in conventional MR imaging. We assessed the geometric distortion of the stereotactic image attached on a Leksell skull frame in conventional and wide-bore 1.5-T MR imaging. Two kinds of acrylic phantoms were placed on the skull frame and were scanned using computed tomography (CT) and conventional and wide-bore 1.5-T MR imaging. The three-dimensional coordinates on both MR imaging were compared with those on CT. Deviations of measured coordinates at selected points (x = 50, 100, 150 mm; y = 50, 100, 150 mm) were indicated on different axial planes (z = 50, 75, 100, 125, 150 mm). The differences of coordinates were less than 1.0 mm in the entire treatable area for conventional MR imaging. With the large bore system, the differences of the coordinates were less than 1.0 mm around the center but substantially exceeded 1.0 mm in the peripheral regions. Further study is needed to increase the geometric accuracy of wide-bore MR imaging for stereotactic radiosurgery treatment planning.

[Dose estimation for exposure conditions of diagnostic radiology acquired by a 2011 questionnaire in a phantom study].

Using a 2011 questionnaire, the Japanese Society of Radiological Technology conducted a nationwide survey on the exposure conditions in diagnostic radiography. The purpose of this study was to measure the entrance surface dose and absorbed dose for each organ dose and to calculate the effective dose using a human phantom with the 2011 exposure conditions. We estimated the patient exposure doses during skull (antero-posterior), chest (postero-anterior), abdomen (antero-posterior), and lumbar vertebrae (antero-posterior, left-right, and right-left) radiographs. The radiation doses were determined by placing 255 thermoluminescence dosimeters at various positions on and in the phantom, including the surface of the skin, head, thyroid, lung, breast, esophagus, stomach, liver, and gonads. The maximum entrance surface dose was 7.83 mGy, which occurred to the lateral lumbar spine. In addition, the minimum entrance surface dose was 0.24 mGy, to the chest. The maximum organ dose was 3.15 mGy, to the stomach of the lateral lumbar vertebrae (LR). Meanwhile, the maximum effective dose was 0.63 mSv, to the lateral lumbar vertebrae (LR). On the contrary, the minimum effective dose was 0.03 mSv, to the head. We could evaluate the entrance surface dose, absorbed dose for each organ dose, and effective doses using the 2011 exposure conditions in Japan. The entrance surface dose of 5 examinations with these exposure conditions was below the guidance level of the IAEA. In the future, it can be said that the entrance surface dose as well as the effective dose require diagnostic reference levels in radiography.

[Comparison MR cholangiopancreatography with 3D-fast recovery fast spin echo in several different slice thicknesses].

PURPOSE: To evaluate the technical quality and visibility of the biliary tree and pancreatic duct on magnetic resonance cholangiopancreatography (MRCP) images obtained with a single-breath-hold three-dimensional (3D) fast-recovery fast spin-echo (FRFSE) sequence in several different slice thicknesses. MATERIALS AND METHODS: As a fundamental study, tubes of various inside diameters filled gadolinium solutions were acquired at 1.5 T in 3D-FRFSE. We observed error rate changes of volume inside the tubes and the visibility of thinner tubes. MRCP was performed at 1.5 T in 8 consecutive patients (4 men and 4 women, aged 22-58 years). Seven radiologists graded images obtained with each slice thickness in a blind fashion. Furthermore, we compared 1.4 mm slice thickness images with 1.8 mm slice thickness images in a continuous rating scale for the same patient. We assessed differences in technical quality, overall visibility, and six individual ductal segments of the biliary tree and pancreatic duct. RESULTS: If slice thickness were thinner relative to diameter, the error rate would be closer to zero. But, when slice thickness was 0.8 mm, the error rate became clearly higher because of low intensity. In the fundamental study, we thought that the appropriate slice thickness is between 1.0 mm and 2.4 mm. The visibility of images of thinner tubes could be improved by having a thinner slice thickness. In particular, MRCP overall images generated from a 1.4 mm slice thickness were found to be significantly superior to those generated from a 1.8 mm slice thickness (p<0.001); this was also true as regards the pancreatic duct and cystic duct (p<0.01, p<0.05). CONCLUSION: We conclude that a 1.4 mm slice thickness is appropriate for MRCP.

Stereotactic imaging for radiosurgery: localization accuracy of magnetic resonance imaging and positron emission tomography compared with computed tomography.

Computed tomography (CT), magnetic resonance imaging (MRI), and positron emission tomography (PET) provide complementary information for treatment planning in stereotactic radiosurgery. We evaluated the localization accuracy of MRI and PET compared with CT. Two kinds of phantoms applicable to the Leksell G stereotactic skull frame (Elekta, Tokyo) were developed. Deviations of measured coordinates at target points (x = 50, 100, 150; y = 50, 100, 150) were determined on different axial planes (z = 30-140 for MRI and CT study and Z = 50-120 for PET and CT study). For MRI, the deviations were no more than 0.8 mm in each direction. For PET, the deviations were no more than 2.7 mm. For both imaging modalities studied, accuracy was at or below the imaging resolution (pixel size) and should be considered useful for clinical stereotactic planning purposes.