FRAC: Fringing-RF-field-activated dc-to-pulse converter for low-energy ion beams

We developed a new type of dc-to-pulse converter, called FRAC (Fringing-RF-field-Activated dc-to-pulse Converter) for low-energy ion beams electrostatically accelerated from an ion source. FRAC is based on a radio-frequency quadrupole (RFQ) linear trap technique and works in principle under ultrahigh vacuum conditions. Ions continuously injected into FRAC are decelerated by an alternating longitudinal electric field produced in a distorted radio frequency field around the edge region of RFQ rods. These ions accumulate in FRAC for a significantly long time. This edge effect appears most notably when the energy of incoming ions exceeds the injection barrier potential by less than a few eV and the energy spread is quite small. The ions stacked during the FRAC operation period are ejected as a high intensity pulsed beam. We investigated the performance of FRAC and the capability of some FRAC operation methods developed to enhance the dc-to-pulse conversion efficiency. The maximum conversion efficiencies achieved were 22% and 5.6% at FRAC operation frequencies of 10 and 1 Hz, respectively. The number of ions contained in an output beam pulse with a duration of 500 μs was in practice 1.6 × 10⁹ ions/pulse at an injected dc beam intensity of 4.6 nA and an operation frequency of 1 Hz.

Exercise-Loaded Indocyanine Green Fluorescence Lymphangiography for Diagnosing Lymphedema

Background Indocyanine green (ICG) fluorescence lymphography (ICGLG) that can visualize the lymphatic vessel and its flow noninvasively and dynamically was developed in 2007. It is frequently used to observe the function and pathway of the lymphatic vessels. ICGLG is simple and easy to perform, and it is useful for understanding the condition of the lymphatic system in real time. However, its protocol is not standardized. In addition, the lymphatic flow is enhanced by an exercise load such as walking. Till now, there is no report of exercise-loaded ICGLG. Therefore, we aimed to shorten the examination time and establish a standard ICGLG protocol.

Methods We examined 63 patients (126 lower limbs) who visited our clinic for lower extremity edema. We observed detailed images of exercise-loaded ICGLG and examined the changes in findings over time in affected legs classified according to the International Society of Lymphedema. After ICG was injected, the participants exercised for 30 minutes. We observed the farthest proximal point where any ICG could be observed and the appearance of dermal backflow (DB), which is a specific finding of lymphedema, every 5 minutes.

Results The proximal migration speed of ICG tended to slow as the disease stage worsened. For all disease stages, after 20 minutes of exercise, the DB appearance rate did not change further. The rates were 0% for legs with stage 0 lymphedema, 50% for legs with stage 1 lymphedema, and 100% for legs with stages 2a and 2b lymphedema.

Conclusion The appropriate exercise duration after ICG injection is 20 minutes. ICGLG is useful for screening for lymphedema.

Fabrication of arrays of tapered silicon micro-/nano-pillars by metal-assisted chemical etching and anisotropic wet etching

Fabrication of a 2D square lattice array of intentionally tapered micro-/nano-silicon pillars by metal-assisted chemical etching (MACE) of silicon wafers is reported. The pillars are square rod shaped with the cross-sections in the range 0.2 × 0.2-0.9 × 0.9 μm² and heights 3-7 μm. The spacing between pillars in the 2D square lattice was controlled between 0.5 and 3.0 μm. While the pillars after MACE had the high aspect ratio ∼1:5, subsequent anisotropic wet etching in potassium hydroxide solution led to 80°-89.5° tapers with smooth sidewalls. The resulting taper angle showed the relation with geometry of pillar structures; the spacing 0.5-3.0 μm led to the tapering angle 89.5°-80° for 3 and 5 μm tall pillars but 7 μm tall pillars showed no dependency between the tapering angle and the inter-pillar spacing. Such an array of silicon tapered-rods with smooth sidewalls is expected to be applicable as a mold in nanoimprinting applications.

Imaging Differences between Neuromyelitis Optica Spectrum Disorders and Multiple Sclerosis: A Multi-Institutional Study in Japan

BACKGROUND AND PURPOSE

Both clinical and imaging criteria must be met to diagnose neuromyelitis optica spectrum disorders and multiple sclerosis. However, neuromyelitis optica spectrum disorders are often misdiagnosed as MS because of an overlap in MR imaging features. The purpose of this study was to confirm imaging differences between neuromyelitis optica spectrum disorders and MS with visually detailed quantitative analyses of large-sample data.

MATERIALS AND METHODS

We retrospectively examined 89 consecutive patients with neuromyelitis optica spectrum disorders (median age, 51 years; range, 16-85 years; females, 77; aquaporin 4 immunoglobulin G-positive, 93%) and 89 with MS (median age, 36 years; range, 18-67 years; females, 68; relapsing-remitting MS, 89%; primary-progressive MS, 7%; secondary-progressive MS, 2%) from 9 institutions across Japan (April 2008 to December 2012). Two neuroradiologists visually evaluated the number, location, and size of all lesions using the Mann-Whitney U test or the Fisher exact test.

RESULTS

We enrolled 79 patients with neuromyelitis optica spectrum disorders and 87 with MS for brain analysis, 57 with neuromyelitis optica spectrum disorders and 55 with MS for spinal cord analysis, and 42 with neuromyelitis optica spectrum disorders and 14 with MS for optic nerve analysis. We identified 911 brain lesions in neuromyelitis optica spectrum disorders, 1659 brain lesions in MS, 86 spinal cord lesions in neuromyelitis optica spectrum disorders, and 102 spinal cord lesions in MS. The frequencies of periventricular white matter and deep white matter lesions were 17% and 68% in neuromyelitis optica spectrum disorders versus 41% and 42% in MS, respectively (location of brain lesions, P < .001). We found a significant difference in the distribution of spinal cord lesions between these 2 diseases (P = .024): More thoracic lesions than cervical lesions were present in neuromyelitis optica spectrum disorders (cervical versus thoracic, 29% versus 71%), whereas they were equally distributed in MS (46% versus 54%). Furthermore, thoracic lesions were significantly longer than cervical lesions in neuromyelitis optica spectrum disorders (P = .001), but not in MS (P = .80).

CONCLUSIONS

Visually detailed quantitative analyses confirmed imaging differences, especially in brain and spinal cord lesions, between neuromyelitis optica spectrum disorders and MS. These observations may have clinical implications.

4D modeling in a gimbaled linear accelerator by using gold anchor markers

Purpose

The purpose of this study was to verify whether the dynamic tumor tracking (DTT) feature of a Vero4DRT system performs with 10-mm-long and 0.28 mm diameter gold anchor markers.

Methods

Gold anchor markers with a length of 10 mm and a diameter of 0.28 mm were used. Gold anchor markers were injected with short and long types into bolus material. These markers were sandwiched by a Tough Water (TW) phantom in the bolus material. For the investigation of 4-dimensional (4D) modeling feasibility under various phantom thicknesses, the TW phantom was added at 2 cm intervals (in upper and lower each by 1 cm). A programmable respiratory motion table was used to simulate breathing-induced organ motion, with an amplitude of 30 mm and a breathing cycle of 3 s. X-ray imaging parameters of 80 kV and 125 kV (320 mA and 5 ms) were used. The least detection error of the fiducial marker was defined as the 4D-modeling limitation.

Results

The 4D modeling process was attempted using short and long marker types and its limitation with the short and long types was with phantom thicknesses of 6 and 10 cm at 80 kV and 125 kV, respectively. However, the loss in detectability of the gold anchor because of 4D-modeling errors was found to be approximately 6% (2/31) with a phantom thickness of 2 cm under 125 kV. 4D-modeling could be performed except under the described conditions.

Conclusions

This work showed that a 10-mm-long gold anchor marker in short and long types can be used with DTT for short water equivalent path length site, such as lung cancer patients, in the Vero4DRT system.

The effects of brain death and ischemia on tolerance induction are organ-specific

We have previously shown that 12 days of high-dose calcineurin inhibition induced tolerance in MHC inbred miniature swine receiving MHC-mismatched lung, kidney, or co-transplanted heart/kidney allografts. However, if lung grafts were procured from donation after brain death (DBD), and transplanted alone, they were rejected within 19-45 days. Here, we investigated whether donor brain death with or without allograft ischemia would also prevent tolerance induction in kidney or heart/kidney recipients. Four kidney recipients treated with 12 days of calcineurin inhibition received organs from donors rendered brain dead for 4 hours. Six heart/kidney recipients also treated with calcineurin inhibition received organs from donors rendered brain dead for 4 hours, 8 hours, or 4 hours with 4 additional hours of cold storage. In contrast to lung allograft recipients, all isolated kidney or heart/kidney recipients that received organs from DBD donors achieved long-term survival (>100 days) without histologic evidence of rejection. Proinflammatory cytokine gene expression was upregulated in lungs and hearts, but not kidney allografts, after brain death. These data suggest that the deleterious effects of brain death and ischemia on tolerance induction are organ-specific, which has implications for the application of tolerance to clinical transplantation.

Image quality and absorbed dose comparison of single- and dual-source cone-beam computed tomography

Purpose

Dual‐source cone‐beam computed tomography (DCBCT) is currently available in the Vero4DRT image‐guided radiotherapy system. We evaluated the image quality and absorbed dose for DCBCT and compared the values with those for single‐source CBCT (SCBCT).

Methods

Image uniformity, Hounsfield unit (HU) linearity, image contrast, and spatial resolution were evaluated using a Catphan phantom. The rotation angle for acquiring SCBCT and DCBCT images is 215° and 115°, respectively. The image uniformity was calculated using measurements obtained at the center and four peripheral positions. The HUs of seven materials inserted into the phantom were measured to evaluate HU linearity and image contrast. The Catphan phantom was scanned with a conventional CT scanner to measure the reference HU for each material. The spatial resolution was calculated using high‐resolution pattern modules. Image quality was analyzed using ImageJ software ver. 1.49. The absorbed dose was measured using a 0.6‐cm³ ionization chamber with a 16‐cm‐diameter cylindrical phantom, at the center and four peripheral positions of the phantom, and calculated using weighted cone‐beam CT dose index (CBCTDI_w).

Results

Compared with that of SCBCT, the image uniformity of DCBCT was slightly reduced. A strong linear correlation existed between the measured HU for DCBCT and the reference HU, although the linear regression slope was different from that of the reference HU. DCBCT had poorer image contrast than did SCBCT, particularly with a high‐contrast material. There was no significant difference between the spatial resolutions of SCBCT and DCBCT. The absorbed dose for DCBCT was higher than that for SCBCT, because in DCBCT, the two x‐ray projections overlap between 45° and 70°.

Conclusions

We found that the image quality was poorer and the absorbed dose was higher for DCBCT than for SCBCT in the Vero4DRT.

[Influence of Changing Respirator Pattern on Dynamic Tumor Tracking Accuracy with Gimbaled Linac System Using a Digital Camera]

It is important for high-precision radiation therapy that tracking accuracy in dynamic tumor tracking (DTT) using the gimbal X-ray head. We evaluated the tracking accuracy under various respiratory patterns differ from a correlation model [four-dimensional model (4D-model)] in real-time using a digital camera. A sheet of paper with luminous line was placed on the programmable respiratory motion table (CIRS Inc.) and operated with the laser projector. The luminous line was defined as a target and the laser was defined as a gimbal. Motion table was operated at a period of 4 s and amplitude of ±10 mm to create 4D-modeling. This movement was defined as the basic operation. To investigate the tracking accuracy, target and gimbal positions were recorded using a digital camera under amplitudes (±5-20 mm) and periods (2-8 s) and analyzed by ImageJ software (NIH). The maximum tracking errors under various period and amplitude were 1.7-0.9 mm and 0.4-1.9 mm, respectively. From the creation of 4D-modeling, it was confirmed that when the period has shortened and the amplitude has increased, tracking accuracy was reduced.

Tolerance levels of CT number to electron density table for photon beam in radiotherapy treatment planning system

The accuracy of computed tomography number to electron density (CT-ED) calibration is a key component for dose calculations in an inhomogeneous medium. In a previous work, it was shown that the tolerance levels of CT-ED calibration became stricter with an increase in tissue thickness and decrease in the effective energy of a photon beam. For the last decade, a low effective energy photon beam (e.g., flattening-filter-free (FFF)) has been used in clinical sites. However, its tolerance level has not been established yet. We established a relative electron density (ED) tolerance level for each tissue type with an FFF beam. The tolerance levels were calculated using the tissue maximum ratio (TMR) and each corresponding maximum tissue thickness. To determine the relative ED tolerance level, TMR data from a Varian accelerator and the adult reference computational phantom data in the International Commission on Radiological Protection publication 110 (ICRP-110 phantom) were used in this study. The 52 tissue components of the ICRP-110 phantom were classified by mass density as five tissues groups including lung, adipose/muscle, cartilage/spongy-bone, cortical bone, and tooth tissue. In addition, the relative ED tolerance level of each tissue group was calculated when the relative dose error to local dose reached 2%. The relative ED tolerances of a 6 MVFFF beam for lung, adipose/muscle, and cartilage/spongy-bone were ±0.044, ±0.022, and ±0.044, respectively. The thicknesses of the cortical bone and tooth groups were too small to define the tolerance levels. Because the tolerance levels of CT-ED calibration are stricter with a decrease in the effective energy of the photon beam, the tolerance levels are determined by the lowest effective energy in useable beams for radiotherapy treatment planning systems.

Determination of reference values for normal cranial morphology by using mid-sagittal vector analysis in Japanese children

Mid-Sagittal Vector Analysis (MSVA) is a method of measuring the distance from a defined central point on the skull surface in the entire mid-sagittal plane and provides a clear description of the lateral view of the skull. We used a series of images of normal skulls of Japanese children to determine normal MSVA values. For this cross-sectional study, we first constructed a database of head CT and MRI images of children aged 0-6 years (41.5 ± 24.9 month (mean ± SD)) who showed no abnormality of cranial development and growth at the time of imaging. Measurement errors due to lateral shifting of the sagittal plane during MSVA were examined, CT and MRI images taken in the same patients at the same time were compared, and measurement differences were examined. Finally, MSVA was carried out, and the mean of the measured values was calculated according to age group. Two hundred ninety-five images were included in the database. When the lateral shifting of the sagittal plane was within 4 mm from the true mid-sagittal plane, the mean errors were less than 1 mm at all measurement points. Between the CT and MRI images from the same patients, most differences in MSVA values were within ±1 mm. These differences were thus acceptable for use in clinical settings. After the above verifications, 220 images were extracted for determination of normal MSVA values. We established a normal dataset of MSVA for Japanese children that can be used effectively for preoperative diagnosis, surgery planning, and postoperative assessment of cranial deformities.

MR Imaging of the Superior Cervical Ganglion and Inferior Ganglion of the Vagus Nerve: Structures That Can Mimic Pathologic Retropharyngeal Lymph Nodes

BACKGROUND AND PURPOSE

The superior cervical ganglion and inferior ganglion of the vagus nerve can mimic pathologic retropharyngeal lymph nodes. We studied the cross-sectional anatomy of the superior cervical ganglion and inferior ganglion of the vagus nerve to evaluate how they can be differentiated from the retropharyngeal lymph nodes.

MATERIALS AND METHODS

This retrospective study consists of 2 parts. Cohort 1 concerned the signal intensity of routine neck MR imaging with 2D sequences, apparent diffusion coefficient, and contrast enhancement of the superior cervical ganglion compared with lymph nodes with or without metastasis in 30 patients. Cohort 2 used 3D neurography to assess the morphology and spatial relationships of the superior cervical ganglion, inferior ganglion of the vagus nerve, and the retropharyngeal lymph nodes in 50 other patients.

RESULTS

All superior cervical ganglions had homogeneously greater enhancement and lower signal on diffusion-weighted imaging than lymph nodes. Apparent diffusion coefficient values of the superior cervical ganglion (1.80 ± 0.28 × 10^-3mm²/s) were significantly higher than normal and metastatic lymph nodes (0.86 ± 0.10 × 10^-3mm²/s, P < .001, and 0.73 ± 0.10 × 10^-3mm²/s, P < .001). Ten and 13 of 60 superior cervical ganglions were hypointense on T2-weighted images and had hyperintense spots on both T1- and T2-weighted images, respectively. The latter was considered fat tissue. The largest was the superior cervical ganglion, followed in order by the retropharyngeal lymph node and the inferior ganglion of the vagus nerve (P < .001 to P = .004). The highest at vertebral level was the retropharyngeal lymph nodes, followed, in order, by the inferior ganglion of the vagus nerve and the superior cervical ganglion (P < .001 to P = .001). The retropharyngeal lymph node, superior cervical ganglion, and inferior ganglion of the vagus nerve formed a line from anteromedial to posterolateral.

CONCLUSIONS

The superior cervical ganglion and the inferior ganglion of the vagus nerve can be almost always differentiated from retropharyngeal lymph nodes on MR imaging by evaluating the signal, size, and position.