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Object Cellular density is a major factor for change in the apparent diffusion coefficient (ADC). The authors hypothesized that loss of tumor cells after Gamma Knife surgery (GKS) may alter the ADC value and used diffusion weighted MR imaging (DW imaging) to evaluate cellular changes in brain tumors to detect their treatment response and the efficacy of GKS. Methods In this paper the authors describe a prospective trial involving 86 patients harboring 38 solid or predominantly solid brain metastases, 30 meningiomas, and 24 acoustic neuromas that were treated by GKS. The patients underwent serial MR imaging examinations, including DW imaging, before treatment and at multiple intervals following GKS. Follow-up MR images and clinical outcomes were reviewed at 3-month intervals for metastatic lesions and at 6-month intervals for benign tumors. Apparent diffusion coefficients were calculated from echoplanar DW images, and mean ADC values were compared at each follow-up. Results The mean ADC value for all meningiomas was 0.82 ± 0.15 × 10−3 mm2/sec before GKS. The mean ADC value as of the last mean follow-up of 42 months was 1.36 ± 0.19 × 10−3 mm2/sec, a significant increase compared to that before treatment (p < 0.0001). Calcification (p = 0.006) and tumor recurrence (p = 0.025) significantly prevented a rise in the ADC level. The mean ADC value for all solid acoustic neuromas was 1.06 ± 0.17 × 10−3 mm2/sec before GKS. The mean ADC value as of the last mean follow-up of 36 months was 1.72 ± 0.26 × 10−3 mm2/sec, a significant increase (p = 0.0002) compared with values before GKS. At the last mean MR imaging follow-up there appeared to be tumor enlargement in 3 patients (12.5%); however, since the ADC values in these patients were significantly higher than the preradiosurgery values, the finding was considered to be a sign of radiation necrosis rather than tumor recurrence. The mean ADC value of metastatic tumors was 1.05 ± 0.12 × 10−3 mm2/sec before GKS. This value rose significantly (p < 0.0001) to 1.64 ± 0.18 × 10−3 mm2/sec after GKS at a mean follow-up of 9.4 months. Magnetic resonance imaging showed that 89% of these tumors had been controlled by GKS. In 2 patients there were enlarged lesions, but the ADC values were the same as pre-GKS levels, and therefore, the lesions were deemed recurrent. Conclusions Apparent diffusion coefficient values may be useful in evaluating treatment results before a definitive change in volume is evident on imaging studies. In some patients in whom imaging findings are equivocal, ADC values may also be used to distinguish radiation-induced necrosis from tumor recurrence.

This paper reports the results of constant speed drag tests on disks with four different lubricants using an ultra-high vacuum (UHV) tribochamber equipped with a mass spectrometer (MS). An optical surface analyzer (OSA) is also used to observe lubricant migration. Based on the analysis of the experimental results, we propose that, in the case of diamond-like carbon (DLC)-coated sliders, the durability of a lubricant is dominated by its mobility, its ability to bond to the carbon overcoat and its thermal stability. However, in the case of uncoated sliders, the durability of the lubricant, is dominated by the strength of the lubricant layer formed on the carbon overcoat, the interaction between lubricant molecules and the Al2O3 of the slider surface, the degradation rate of the lubricants caused by catalysis of Al2O3, as well as thermal stability of lubricant. Reaction of Al2O3 with the oxygen atoms in the backbones of the molecules is the dominant factor in their catalytic degradation.

The optical surface analyzer (OSA) was found to be an excellent tool to examine the lubricant migration rate on thin film disks. Using the OSA it was found that the rate of lubricant migration increased as molecular weight decreased. An AM type perfluoropolyether with an aromatic end group and Z-Dol were also observed to have different migration rates for the same molecular weight. The migration rate of AM lubricant was increased significantly by the presence of X-1P as an additive in the lubricant system.

Fly-stiction is a special kind of stiction that occurs at the interface between a hard drive head and the hard disk. It can have very high values and has caused serious problems for the computer industry in the past. It is defined as that taken after a certain number of CSS cycles in the landing zone of a disk, followed by an extended period of time of sweep or track dwell in the data zone and finally an extended period of park time in the landing zone. This paper has studied the nature, mechanism and solutions of the high fly-stiction phenomenon. CSS testers, optical microscopes, an optical surface analyzer and a Fourier transform infrared spectrometer were used to measure fly-stiction values and analyze the test surfaces of heads and disks. The results obtained indicate that the fly-stiction value is much higher than the corresponding park-stiction value. The fly-stiction value does not change with increasing number of CSS cycles, and may decrease slightly with increasing lubricant thickness. In addition, a high fly-stiction value may be caused by a contamination of spindle grease. Finally, a high fly-stiction value can be reduced by avoiding contamination or increasing the resistance to contamination of a disk. For instance, an ion-beam carbon overcoat can reduce the fly-stiction to half the value obtained with a sputter carbon overcoat.

Thermal asperities (TA’s) are tribological events that cause repercussions for giant magnetoresistance (GMR) and MR heads in the hard disk drive industry. A TA is a read signal spike caused by sensor temperature rise due to contact with disk asperities or contaminant particles. TA events may cause GMR and MR heads to temporarily lose their reading capability, and may potentially damage the transducer. It is difficult to completely avoid particle contamination in hard drive applications. Hence it is necessary to design heads/media with a minimum TA sensitivity to particles. A test method for TA sensitivity to particles is needed. This work developed a test method for TA sensitivities to particles. The test system includes a CSS tester with TA detection capability, a chamber to contain the head/disk interface, a particle atomizer, and a particle counter. Aluminum silicate particles used in the test have sizes ranging from 0.2 to 1.0 μm. Particles are injected into the chamber during head scan for TA’s from ID to OD with adjustable air-borne concentrations in the chamber from 10×106 to 30×106particles/m3. TA counts of 30 scans are averaged to obtain reliable TA sensitivity data. Media with different lubricant thickness, different carbon overcoats, and different lubricant types are tested with this method. The results indicated that this methodology can effectively differentiate TA sensitivity to particles for the media studied.

Cellular density is a major factor for change in the apparent diffusion coefficient (ADC). The authors hypothesized that loss of tumor cells after Gamma Knife surgery (GKS) may alter the ADC value and used diffusion weighted MR imaging (DW imaging) to evaluate cellular changes in brain tumors to detect their treatment response and the efficacy of GKS.In this paper the authors describe a prospective trial involving 86 patients harboring 38 solid or predominantly solid brain metastases, 30 meningiomas, and 24 acoustic neuromas that were treated by GKS. The patients underwent serial MR imaging examinations, including DW imaging, before treatment and at multiple intervals following GKS. Follow-up MR images and clinical outcomes were reviewed at 3-month intervals for metastatic lesions and at 6-month intervals for benign tumors. Apparent diffusion coefficients were calculated from echo planar DW images, and mean ADC values were compared at each follow-up.The mean ADC value for all meningiomas was 0.82 ± 0.15 × 10-3 mm2/sec before GKS. The mean ADC value as of the last mean follow-up of 42 months was 1.36 ± 0.19 × 10-3 mm2/sec, a significant increase compared to that before treatment (p0.0001). Calcification (p = 0.006) and tumor recurrence (p = 0.025) significantly prevented a rise in the ADC level.The mean ADC value for all solid acoustic neuromas was 1.06 ± 0.17 × 10-3 mm2/sec before GKS. The mean ADC value as of the last mean follow-up of 36 months was 1.72 ± 0.26 × 10-3 mm2/sec, a significant increase (p =0.0002) compared with values before GKS. At the last mean MR imaging follow-up there appeared to be tumor enlargement in 3 patients (12.5%); however, since the ADC values in these patients were significantly higher than the preradiosurgery values, the finding was considered to be a sign of radiation necrosis rather than tumor recurrence. The mean ADC value of metastatic tumors was 1.05 ± 0.12 × 10-3 mm2/sec before GKS. This value rose significantly(p0.0001) to 1.64 ± 0.18 × 10-3 mm2/sec after GKS at a mean follow-up of 9.4 months. Magnetic resonance imaging showed that 89% of these tumors had been controlled by GKS. In 2 patients there were enlarged lesions, but the ADC values were the same as pre-GKS levels, and therefore, the lesions were deemed recurrent.Apparent diffusion coefficient values may be useful in evaluating treatment results before a definitive change in volume is evident on imaging studies. In some patients in whom imaging findings are equivocal, ADC values may also be used to distinguish radiation-induced necrosis from tumor recurrence.(DOI: 10.3171/2010.7.GKS10864)

Spinstand level testing has demonstrated a failure mechanism that may go undetected using standard strain gage and acoustic emission methods of data capture. Since normally static friction is higher than dynamic friction, dynamic friction measurements are often ignored, filtered, or sampled at a much lower data rate than static friction measurements. In this study, dynamic friction peak values significantly higher than the static friction were recorded during take-off of Pico heads on laser-textured media. Furthermore, data collected using an optical surfaceanalyzer (OSA) showed a greater degree of wear on disks exhibiting high dynamic friction. FFT was employed to analyze the signal modulation of the high dynamic friction event. Resonance at a frequency of approximately 1050 Hz was found to be associated with the high dynamic friction.Experiments were designed to reveal factors that influence this resonance occurrence. The factors identified that contribute to this resonance were natural frequency of the head load arm, disk bump pitch, and lubricant thickness. The head/disk interface system is believed to be excited by an improper bump pitch if the lubricant layer is not thick enough to reduce the friction value.

Digital circuit design is being challenged by ever-increasing design complexity and continuously shrinking transistor size. For high yield, we have to devote more to the design process, and the verifications carried during the design are becoming increasingly important. This paper takes a standard cell based DSP (digital signal processor) design as a case study to show the verification techniques adopted during the design process. This DSP is dedicated to a cochlear implant system. These methodologies form the architecture of multilevel verification. This multilevel verification architecture is not only well suited in our design, but can also be taken as a guideline to general ASIC (application specified integrated circuit) design process.

ObjectRepeated Gamma Knife surgery (GKS) for trigeminal neuralgia (TN) is an acceptable method for refractory cases but not well established in terms of dose effect and nerve tolerance. The authors report their experience in 28 patients over 3.5 years of follow up.MethodsBetween 1999 and 2004, a total of 28 patients with recurrent or residual TN underwent repeated GKS. The median follow-up periods were 52 and 43 months after the first and repeated procedures, respectively. The entry zone of the trigeminal nerve was targeted using a 4-mm collimator and treated with 40 to 76 Gy as maximal dose. Additive doses ranged between 110 and 152 Gy. The median duration of symptoms was 4.86 years. There were 12 women (46%) and 16 men (54%).At the last evaluation, a total of 19 patients (68%) reported pain relief. Of these patients, 13 were no longer taking pain medications. Significant recurrent or residual pain was noted in nine patients after a median follow up of 12 months (range 6–48 months). New onset of facial numbness was noted in 10 patients. An additive dose above 115 Gy was found to be associated with facial numbness and nonfacial numbness (p = 0.047). No definite additive dose correlation with pain relief was noted (p = 0.23).Conclusions Repeated GKS established durable pain relief in a majority of patients, and a higher additive dose (> 115 Gy) tended to cause facial numbness. However, a prospective trial is needed to fully assess the efficacy and late complications of GKS.

ObjectThe results of microsurgery in patients with trigeminal neuralgia (TN) after failure of repeated Gamma Knife surgery (GKS) have not previously been examined. The effects of microvascular decompression (MVD) in patients in whom repeated GKS has failed are reported.MethodsBetween 1999 and 2004, eight patients (five women and three men) who underwent repeated GKS and experienced treatment failure subsequently underwent MVD. These patients underwent MVD for recurrent or residual intractable trigeminal pain. The duration of facial pain before MVD ranged from 0.8 to 13 years (mean 5.2 years). The total treatment dose administered ranged from 110 to 140 Gy (mean 129 Gy). The mean age was 59.5 years (range 44–68 years). Seven patients in whom the offending vessel (five arteries and two veins) was located at the nerve entry zone improved with variable pain relief after MVD. One patient in whom the vessel could not be identified did not improve. Intraoperatively, there were no signs in any patient of radiation-induced damage such as thickening of arachnoid membrane. In one patient a segment of atherosclerotic plaque was discovered at the nerve entry zone. Two patients experienced numbness at 1 and 3 months after MVD.Conclusions Microvascular decompression is an effective treatment for patients with TN in whom repeated GKS has failed. Previous radiation treatment did not negatively impact operative difficulty or risk to the patient in this small series. Radiosurgery may induce vascular injury and cause pain recurrence.