Critical energies for SSB and DSB induction in plasmid DNA by low-energy photons: action spectra for strand-break induction in plasmid DNA irradiated in vacuum

PURPOSE: To measure action spectra for the induction of single-strand breaks (SSB) and double-strand breaks (DSB) in plasmid DNA by low-energy photons and provide estimates for the energy dependence of strand-break formation important for track-structure simulations of DNA damage. MATERIALS AND METHODS: Plasmid pMSG-CAT was irradiated as a monolayer, under vacuum, with 7 150eV photons produced by a synchrotron source. Yields of SSB and DSB were determined by the separation of the three plasmid forms by gel electrophoresis. RESULTS: The yields of SSB per incident photon increased from 1.4x 10(-15) SSB per plasmid per photon/cm2 at 7eV to 7.5 x 10(-14) SSB per plasmid per photon/cm2 at 150 eV. Direct induction of DSB was also detected increasing from 3.4 x 10(-17) DSB per plasmid per photon/cm2 at 7eV to 4.1 x 10(-15) DSB per plasmid per photon/cm2 at 150eV. When the absorption cross-section of the DNA was considered, the quantum efficiency for break formation increased over the energy range studied. Over the entire energy range, the ratio of SSB to DSB remained constant. CONCLUSIONS: These studies provide evidence for the ability of photons as low as 7 eV to induce both SSB and DSB. The common action spectrum for both lesions suggests that they derive from the same initial photoproducts under conditions where the DNA is irradiated in vacuum and a predominantly direct effect is being observed. The spectral and dose-effect behaviour indicates that DSB are induced predominantly by single-event processes in the energy range covered.     

Critical energies for SSB and DSB induction in plasmid DNA by low-energy photons: action spectra for strand-break induction in plasmid DNA irradiated in vacuum

Purpose : To measure action spectra for the induction of single-strand breaks (SSB) and double-strand breaks (DSB) in plasmid DNA by low-energy photons and provide estimates for the energy dependence of strand-break formation important for track-structure simulations of DNA damage. Materials and methods : Plasmid pMSG-CAT was irradiated as a monolayer, under vacuum, with 7-150 eV photons produced by a synchrotron source. Yields of SSB and DSB were determined by the separation of the three plasmid forms by gel electrophoresis. Results : The yields of SSB per incident photon increased from 1.4 x 10 -15 SSB per plasmid per photon/cm 2 at 7 eV to 7.5 x 10 -14 SSB per plasmid per photon/cm 2 at 150 eV. Direct induction of DSB was also detected increasing from 3.4 x 10 -17 DSB per plasmid per photon/cm 2 at 7 eV to 4.1 x 10 -15 DSB per plasmid per photon/cm 2 at 150 eV. When the absorption cross-section of the DNA was considered, the quantum efficiency for break formation increased over the energy range studied. Over the entire energy range, the ratio of SSB to DSB remained constant. Conclusions : These studies provide evidence for the ability of photons as low as 7 eV to induce both SSB and DSB. The common action spectrum for both lesions suggests that they derive from the same initial photoproducts under conditions where the DNA is irradiated in vacuum and a predominantly direct effect is being observed. The spectral and dose-effect behaviour indicates that DSB are induced predominantly by single-event processes in the energy range covered.     

The rete mirabile of the eel: a useful model for the study of transcapillary passage of MR contrast agents

Our purpose was to study the capillary leakage of MR contrast media using a pure capillary model, the rete mirabile of the eel. The rete is a countercurrent-exchange organ composed of an arterial and a venous capillary system that can be catheterized and perfused. Substances are introduced at the arterial input by a constant infusion, and their steady-state concentrations are measured at the arterial and venous outputs. The capillary leakage of four MR contrast agents--Gd-DOTA(MW = 561 D), carboxymethyldextran-Gd-DTPA (MW = 38,900 D), albumin-Gd-DTPA (MW = 92,000 D), AMI-227 (400,000 D相似文献   

Analysis of diffusion changes in posttraumatic bone marrow using navigator-corrected diffusion gradients

OBJECTIVE: This study was undertaken to analyze diffusion characteristics of normal and posttraumatic bone marrow. MATERIALS AND METHODS: Fifty consecutive patients with knee pain underwent both conventional and diffusion-weighted MR imaging (b values, 0-980 sec/mm2). Diffusion maps derived from source data were analyzed on a workstation using region-of-interest techniques. Apparent diffusion values recorded in normal marrow were compared with values recorded in abnormal posttraumatic bone marrow (square centimeters per second). RESULTS: Normal bone marrow identified in 35 patients showed minimal diffusion, with a mean value of 0.15x10(-5) cm2/sec. Bone marrow in 15 patients sustaining direct traumatic injury (21 bone bruises) showed markedly increased diffusion, with a mean value of 0.8x10(-5) cm2/sec (range, 0.4-1.3 cm2/sec). CONCLUSION: Marrow injury after trauma with trabecular damage allows increased movement or diffusion of interstitial water relative to normal marrow. The magnitude of diffusion change appears to reflect the severity of marrow injury.     

Anatomical distribution of 3He apparent diffusion coefficients in severe chronic obstructive pulmonary disease

PURPOSE: To evaluate the anatomical distribution of apparent diffusion coefficients (ADC) using hyperpolarized helium-3 (3He) MRI in chronic obstructive pulmonary disease (COPD). MATERIALS AND METHODS: Hyperpolarized 3He MRI was performed in eight healthy and seven COPD subjects under breathhold conditions in the supine position to determine ADC values from diffusion-weighted images and evaluate anterior-posterior (AP) and superior-inferior (SI) differences. RESULTS: ADC differences between anterior and posterior slices, DeltaAP, was 0.06 +/-0.01 cm2/second for healthy volunteers and 0.04 +/-0.02 cm2/second for COPD subjects and was significant for each subject (P < 0.01). The AP ADC gradient was -3.98 x 10(-3) +/-0.59 cm2/second/cm for healthy volunteers and -2.04 x 10(-3) +/-0.89 cm2/second/cm for COPD subjects. The difference in ADC between superior and inferior regions of interest (ROIs), DeltaSI, was 0.02 +/-0.02 cm2/second for healthy volunteers and 0.10 +/-0.09 cm2/second for COPD subjects, which was significant for each subject (P < 0.05). The SI ADC gradient was -0.63 x 10(-3) +/-2.23 cm2/second/cm for healthy volunteers and -6.61 x 10(-3) +/-6.68 cm2/second/cm for COPD subjects. DeltaAP, AP-gradient, and SI-gradient were significantly different between healthy volunteers and COPD subjects (P < 0.05). CONCLUSION: In all subjects, ADC anatomical differences were significant and mean ADC was dependent on anatomic location and disease status.     

Sorption and diffusion behavior of Cs and Sr on Jih-Hsing bentonite.

Sorption and diffusion are important processes for the transport of radionuclides through buffer materials such as bentonite. In this study, the sorption and diffusion behaviors of Cs and Sr on Jih-Hsing bentonite are investigated using batch and through-diffusion techniques. The distribution coefficients (Kds) of Cs and Sr from batch experiments are approximately 1200 ml/g and 800 ml/g, respectively. It is found that the Freundlich isotherm model could fit the sorption isotherm with an equilibrium concentration of 10(-7)-10(-1) N. The calculated retardation factors (Rds) for samples at densities of 1.8 g/cm3, 2.0 g/cm3 and 2.2 g/cm3 are 5685, 7744, and 11000 for Cs, and are 3790, 5162, and 7334 for Sr. For the through-diffusion experiments on the compacted samples with the same densities, the corresponding apparent diffusion coefficients for Cs are (2.83+/-0.75) x 10(-13) m2/s, (1.97+/-0.02) x 10(-13) m2/s, and (1.91+/-0.12) x 10(-13) m2/s, respectively. The corresponding apparent diffusion coefficients for Sr are (1.33+/-0.13) x 10(-13) m2/s, (1.51+/-0.15) x 10(-13) m2/s, and (1.34+/-0.10) x 10(-13) m2/s. The Rds obtained from the diffusion experiments for sample densities of 1.8 g/cm3, 2.0 g/cm3 and 2.2 g/cm3 are 1166+/-355, 2113+/-123, 2796+/-171 for Cs, and 713+/-258, 510+/-68, 846+/-158 for Sr. It appears that the retardation factors obtained from the diffusion experiments are about one order of magnitude lower than those derived from the batch experiments. The discrepancy and the possible explanations are discussed in the paper.     

Hypofractionated Stereotactic Radiotherapy for Brain Metastases

PURPOSE: To evaluate efficacy and toxicity of hypofractionated stereotactic radiotherapy (hfSRT) with three different dose concepts for irresectable brain metastases not amenable to radiosurgery (SRS) using non-invasive fixation of the skull. PATIENTS AND METHODS: From 6/2000 to 6/2005, 150 patients with 228 brain metastases were treated at the dedicated stereotactic radiosurgery system Novalis (BrainLAB, Feldkirchen, Germany) in two German treatment centers. Three different dose concepts were applied: 5 x 6-7 Gy (A: 72 brain metastases), 10 x 4 Gy (B: 59 brain metastases) and 7 x 5 Gy (C: 97 brain metastases). Median planning target volume (PTV) was 6.1 cm(3) (range, 0.02-95.97). RESULTS: Rates of complete remission (CR), partial remission (PR), no change (NC) and progressive disease (PD) were 42%, 30%, 21% and 7%, respectively (median follow-up 28 months). Median survival was 16 months. Survival at 6 and 12 months was 83% and 66%, respectively. Side effects were dependent on the PTV and on dose concept (median PTV in case of increasing edema or necrosis: 17 cm3, A: 22%, C: 7%). HfSRT with 10 x 4 Gy (B) was well tolerated without side effects. CONCLUSION: Hypofractionated stereotactic radiotherapy is an effective and safe treatment. In case of brain metastases >15 cm(3) (diameter >3 cm) and concerning toxicity, 10 x 4 Gy seem to be more advantageous than shorter fractionation with higher doses while 5 x 6-7 Gy and 7 x 5 Gy were followed by higher response rates. Further specification of tolerance doses and tolerance according to the different brain regions has to be done.     

175Yb-labeled hydroxyapatite: a potential agent for use in radiation synovectomy of small joints

The preparation of 175Yb-labeled hydroxyapatite (HA) particle is described for possible use as an agent for radiation synovectomy (RS) of small-sized joints. 175Yb was produced by thermal neutron irradiation of enriched (98.6% in 174Yb) ytterbium target at a flux of approximately 3 x 10(13) n/cm(2)/s for 7 days. Specific activity of 5.5-6.0 GBq/mg and a very high radionuclidic purity to the extent of approximately 100% were obtained. In the work reported herein, HA could be labeled with 175Yb in very high radiochemical purity (>99%) using 10 mg of HA particle at pH approximately 7. The radiolabeled particulates showed excellent in vitro stability at room temperature. Serial scintigraphic images of normal as well as arthritis-bearing Wistar rats following intra-articular injection of 175Yb-HA particles in the knee joint showed complete retention of activity within the synovial cavity with no measurable activity leaching out from the joint till 144 h post-injection.     

高功率微波辐射对大鼠血脑屏障的影响

目的：研究高功率微波辐射对大鼠血脑屏障结构和功能的影响。方法：以10、30和100mW／cm^2高功率微波源辐射66只二级雄性Wistar大鼠。于辐射后6h、1d、3d和7d灌注2％亚铁氰化钾和4．2％硫酸铁后取材，通过HE染色、组织化学、免疫组化和图像分析等技术，研究毛细血管形态、血脑屏障通透性及GFAP改变。结果：10mW／cm^2组大鼠血脑屏障无明显改变。30和100mW／cm^2组辐射后1～3d血管间隙增宽，组织水肿，指示剂通透性增加。上述改变于辐射后3d达高峰，7d基本恢复。皮质血管较海马血管改变明显，100mW／cm^2组重于30mW／cm^2组。30和100mW／cm^2组大鼠皮质和海马组织中GFAP表达增强，3d达高峰，7d仍高于假辐射组。结论：一定剂量高功率微波辐射可损伤大鼠血脑屏障结构和功能。     

Renovation of epithermal neutron beam for BNCT at THOR.

Heading for possible use for clinical trial, THOR (Tsing Hua Open-pool Reactor) at Taiwan was shutdown for renovation of a new epithermal neutron beam in January 2003. In November 2003, concrete cutting was finished for closer distance from core and larger treatment room. This article presents the design base that the construction of the new beam is based on. The filter/moderator design along the beam is Cd(0.1cm)+Al(10 cm)+FLUENTAL (16 cm)+Al(10 cm)+FLUENTAL(24 cm)+Void(18 cm)+Cd(0.1cm)+Bi(10 cm) with 6 cm Pb as reflector. Following the filter/moderator is an 88 cm long, 6 cm thick Bi-lined collimator with Li(2)CO(3)-PE at the end. The collimator is surrounded by Li(2)CO(3)-PE and Pb. The calculated beam parameters under 2 MW at the beam exit is phi(epi) = 3.4 x 10(9) n/cm(2)/s, Df/phi(epi) = 2.8 x 10(-11) cGy cm(2)/n, Dgamma/phi(epi) = 1.3 x 10(-11) cGy cm(2)/n, and J+/phi = 0.8. For a phantom placed 10 cm from beam exit, MCNP calculation shows that the advantage depth is 8.9 cm, and advantage ratio is 5.6 if boron concentration in tumor and normal tissue are assumed to be 65 and 18 ppm. The maximum dose rate for normal tissue is 50 cGy/min. The maximum therapeutic ratio is 6. The construction of the beam is scheduled to be finished by the end of April 2004.     

Critical energies for ssb and dsb induction in plasmid DNA by vacuum-UV photons: an arrangement for irradiating dry or hydrated DNA with monochromatic photons

PURPOSE: Theoretical modelling techniques are often used to simulate the action of ionizing radiations on cells at the nanometre level. Using monoenergetic vacuum-UV (VUV) radiation to irradiate DNA either dry or humidified, the action spectra for the induction of DNA damage by low energy photons and the role of water and can be studied. These data provide inputs for the theoretical models. METHODS: Various combinations of monochromator, grating and VUV window have been used to obtain monochromatic photons from the 2 GeV electron synchrotron at the CLRC, Daresbury Laboratory. A sample chamber containing plasmid DNA is installed at the end of the beamline. The chamber can be evacuated or water can be introduced (as water vapour or humidified helium). In this way, DNA can be irradiated either dry or humidified. RESULTS: An arrangement for irradiating dry or humidified DNA using monoenergetic photons from 7 eV to 150 eV has been developed. At the energies used, exposure rates vary from about 5 x 10(10) to 3 x 10(12) photons cm(-2) s(-1) over a 1 cm2 sample area. At all but the lowest energies this is sufficient to produce significant levels of DNA damage in just a few minutes. The measured dose variation over the sample area is typically 30%, but this is reduced significantly using sample scanning techniques.     

Preparation and bioevaluation of 166Ho labelled hydroxyapatite (HA) particles for radiosynovectomy

The preparation of 166Ho labeled hydroxy apatite (HA) particles for radiosynovectomy applications is described in this paper. 166Ho was prepared by the irradiation of Ho2O3 at a flux of 1.8 x 10(13) neutrons/cm2/s for about 7 days. The irradiation resulted in the production of approximately 17 GBq of 166Ho activity at the end of six hours post end of bombardment and the corresponding specific activity was approximately 3-4 GBq/mg of Ho. The irradiated target was dissolved in 0.1 N HCl solution. Radionuclidic purity was ascertained by high resolution gamma ray spectrometry. HA particles were synthesized and characterized by X-ray diffractometry. Labeling studies were carried out with and without citric acid as a transchelating agent. Radiochemical yield and purity of the 166Ho-HA particles were ascertained by paper chromatography and by paper electrophoresis techniques. Labeling yield of >98% could be achieved at pH 7, with 40 mg of HA particles and 8.6 microg of Ho. 166Ho-HA particles prepared were stable for 72 h. Bio-evaluation of the 166Ho -HA particles were carried out by injecting approximately 74 MBq dose in 200 microL (approximately 8 mg of 166Ho-HA particles) directly into the arthritis induced knee joints as well as into the healthy knee joints of white New Zealand rabbits. Images of the injected joints of the animals recorded using a gamma camera at regular intervals showed good retention. Blood samples were collected from the animals and activity assayed in a scintillation detector. Experiments were also carried out under identical conditions in normal rabbits. In both the cases, it was observed that there was no significant extra articular leakage of the injected activity over the study period of 96 h post injection.     

Anisotropic and restricted diffusion of water in the sciatic nerve: A (2)H double-quantum-filtered NMR study.

The signals of water in the different compartments of rat sciatic nerve are resolved in the (2)H double-quantum-filtered NMR spectrum, due to their different quadrupolar splittings and relaxation rates. This resolution allowed the independent measurement of the water diffusion coefficients in the different compartments. The water diffusion in all three compartments, the endoneurium, the epineurium and the axon was found to be anisotropic. Parallel to the nerve fiber the average intraxonal water diffusion coefficient was 1.11 x 10(-5) cm(2)/sec, while in the perpendicular direction the diffusion is heavily restricted. The average perpendicular diffusion coefficient ranged from 0.29 x 10(-5) cm(2)/sec to 0.05 x 10(-5) cm(2)/sec for diffusion times of 7 msec and 50 msec, respectively. Assuming restricted diffusion in nonpermeable cylinders, intra-axonal mean diameters of 6.0, 7.4 and 9.0 microm were obtained for nerves taken from three different rats. Magn Reson Med 42:461-466, 1999.     

Preparation and in vitro stability of (n,gamma) yttrium-90 hydroxyapatite.

Yttrium-90, produced by irradiating Y2O3 (15 mg) in the Pakistan Research Reactor (PARR-I) at a flux of approximately 1.5x10(14) neutrons/cm2/s, was used to prepare yttrium-90 hydroxyapatite particles for radiosynovectomy applications. The irradiated material was dissolved in concentrated hydrochloric acid, evaporated and taken up in distilled water. The 120 h irradiation resulted in the production of approximately 12GBq (324mCi) of 90Y at the end of irradiation (EOI) and the corresponding specific activity was approximately 1017GBq/g of yttrium. Hydroxyapatite (HA) particles were synthesized by an already reported method. Labeling of HA particles with 90Y was studied without a transchelating agent. Labeling yields of approximately 100% could be achieved with 40 mg of HA and 0.4 mg of 90Y. In vitro studies showed <2% loss of 90Y activity in normal saline and 1% human serum albumin solution over a period of 8 days. The high labeling yield, good stability and ease of preparation of the 90Y-HA particles indicate that these particles may find wide application in radiation synovectomy.     

Monte Carlo simulation of surface percent depth dose.

This work studied the surface percent depth dose of 6 and 15 MV X-rays, 10 x 10 cm2 and 20 x 20 cm2 fields by Monte Carlo simulation. The OMEGA/BEAM code, an EGS4 user code developed by the NRCC, was used. The linac, Siemens PRIMUS, was accurately modeled according to the ion chamber and CEA film measurement, and the phase space data generated from this linac were collected to simulate dose distribution in water. The water phantom had radius 30 cm and thickness 10 cm. The percent depth doses at zero depth, PDDsurface, for 6 MV X-rays were 13.85 +/- 0.11% and 23.21 +/- 0.20% for the 10 x 10 cm2 and 20 x 20 cm2 fields, respectively. For 15 MV X-rays, PDDsurface values were 8.83 +/- 0.07% and 18.60 +/- 0.12% for the 10 x 10 cm2 and 20 x 20 cm2 fields, respectively.     

Diffusion-weighted magnetic resonance imaging: a potential non-invasive marker of tumour aggressiveness in localized prostate cancer

AIM: To evaluate diffusion-weighted magnetic resonance imaging (DW-MRI) as a marker for disease aggressiveness by comparing tumour apparent diffusion coefficients (ADCs) between patients with low- versus higher-risk localized prostate cancer. METHOD: Forty-four consecutive patients classified as low- [n = 26, stageT1/T2a, Gleason score < or = 6, prostate-specific antigen (PSA)< 10 (group 1)] or intermediate/high- [n = 18, stage > or = T2b and/or Gleason score > or = 7, and/or PSA > 10 (group 2)] risk, who subsequently were monitored with active surveillance or started neoadjuvant hormone and radiotherapy, respectively, underwent endorectal MRI. T2-weighted (T2W) and DW images (5 b values, 0-800 s/mm(2)) were acquired and isotropic ADC maps generated. Regions of interest (ROIs) on T2W axial images [around whole prostate, central gland (CG), and tumour] were transferred to ADC maps. Tumour, CG, and peripheral zone (PZ = whole prostate minus CG and tumour) ADCs (fast component from b = 0-100 s/mm(2), slow component from b = 100-800 s/mm(2)) were compared. RESULTS: T2W-defined tumour volume medians, and quartiles were 1.2 cm(3), 0.7 and 3.3 cm(3) (group 1); and 6 cm(3), 1.3 and 16.5 cm(3) (group 2). There were significant differences in both ADC(fast) (1778 +/- 264 x 10(-6) versus 1583 +/- 283 x 10(-6) mm(2)/s, p = 0.03) and ADC(slow) (1379 +/- 321 x 10(-6) versus 1196 +/- 158 x 10(-6) mm(2)/s, p = 0.001) between groups. Tumour volume (p = 0.002) and ADC(slow) (p = 0.005) were significant differentiators of risk group. CONCLUSION: Significant differences in tumour ADCs exist between patients with low-risk, and those with higher-risk localized prostate cancer. DW-MRI merits further study with respect to clinical outcomes.     

Radiation effect of gadolinium-neutron capture reactions on the survival of Chinese hamster cells

In gadolinium-neutron capture reactions, prompt gamma rays with an energy spectrum of up to 7 MeV, X-rays and electrons are released. We measured the effect of radiation as a result of capture reactions on cultured Chinese hamster cells. Cells in the medium containing 5000 ppm gadolinium were exposed to thermal neutrons from a nuclear reactor. The survival curve for those cells exhibited a shoulder in the low neutron fluence region. The survival curve for cells exposed to thermal neutrons in the absence of gadolinium was a simple exponential function. To obtain 10% survival levels, 5.4 x 10(12) neutrons/cm2 were required for cells irradiated in the absence of gadolinium, and 1.55 x 10(12) neutrons/cm2 for those irradiated in the presence of gadolinium. The therapeutic ratio in gadolinium-neutron capture therapy depends on the difference in 157Gd concentrations between the tumor and normal tissues. Thus, our current effort has been to develop a method of selectively delivering 157Gd to tumors.     

Das Verletzungspotential von Kartuschenmunition im Gelatinemodell

In order to describe the wounding capacity in standardized manner, gelatine was used to simulate biological targets in terminal ballistics. The aim was the investigation of blank cartridges with wound ballistic methods. Blank cartridges (caliber 9 mm × 17) produced by RWS, SM, Wadie and Umarex were fired with starter’s revolvers of .380 caliber into 10% gelatine blocks. Shots were fired at 4?°C at distances ranging from close contact and from 1 up to 50 cm distance. The blocks of gelatine and their cross-sections were photographed using slide film which was digitized and analyzed by computer. Contact shots produced penetration from 21 to 63 mm in depth and the maximum diameter of the wound cavity measured from 7 to 42 mm. Up to a distance of 4 cm black powder blank cartridges produced tearing of more than 1 cm depth. Shots from a distance of 10 cm propelled many particles up to 13 mm deep into the gelatine. At a shooting range of 50 cm 13% of the particles penetrated deeper than 3 mm and some penetrated up to 7 mm. The experimental findings give evidence of the well known risk of fatal injury from contact shots. Up to a shooting range of 5 cm injuries of the eye bulb are to be expected and at a 50 cm distance severe lesions of the cornea.     

Performance evaluation of a modular gamma camera using a detectability index.

The performance of a modular gamma camera for the task of detecting signals in random noisy backgrounds was evaluated experimentally. The results were compared with a theoretical computer simulation. METHODS: The camera uses a 10 x 10 cm thallium-doped sodium iodide crystal, a 2 x 2 array of 53 x 53 mm photomultiplier tubes, and a parallel-hole collimator (1.5-mm bore width, 23.6-mm bore length). The camera was positioned to look down into a 10-cm-deep water bath that filled its field of view (FOV). The top surface of the water was 5 cm from the front face of the camera. The camera has 3-mm intrinsic spatial resolution (SR) in the center of its FOV and 9-mm system SR for objects 5 cm below the top surface of the water. Uniform and nonuniform random background data were collected by imaging the bath containing 740 MBq (20 mCi) (99m)Tc. Nonuniformities were created by placing water-filled objects in the bath. Each signal dataset was collected by imaging a water-filled plastic sphere, injected with (99m)Tc and set at a specific depth (Z) in the bath. Data were collected for many signal diameters (D) (4, 7, 10, 13, 16, 28 mm) at 1 depth (5 cm) and for 1 signal diameter (10 mm) at several depths (1, 3, 5, 7, 9 cm). Sets of signal-present/signal-absent image pairs (380 pairs, 10(5) events per image) for known contrasts (C) were generated for use in ideal-observer studies in which the detectability (d') was calculated. Contrast-detail (log C vs. log D) plots were created. The theoretical simulation, developed for uniform backgrounds, provided data for comparison. RESULTS: The detectability increased linearly with C and decreased nonlinearly with decreasing D or increasing Z. The C required to achieve a specific d' increased sharply for D < SR. For C = 5, D = 10 mm, and d' = 1.2, the camera consistently detected signals for Z < 6 cm. Similar results were found for nonuniform backgrounds. The theoretical simulation verified the results for uniform backgrounds. CONCLUSION: The methodology presented here provides a way of evaluating gamma cameras on the basis of signal-detection performance for specified lesions, with particular application to scintimammography.     

In vivo measurement of the apparent diffusion coefficient in normal and malignant prostatic tissues using echo-planar imaging

PURPOSE: To measure for the first time the apparent diffusion coefficient (ADC) values in anatomical regions of the prostate for normal and patient groups, and to investigate its use as a differentiating parameter between healthy and malignant tissue within the patient group. MATERIALS AND METHODS: Single-shot diffusion-weighted echo-planar imaging (DW-EPI) was used to measure the ADC in the prostate in normal (N = 7) and patient (N = 19) groups. The spin-echo images comprised 96 x 96 pixels (field of view of 16 cm, TR/TE = 4000/120 msec) with six b-factor values ranging from 64 to 786 seconds/mm(2). RESULTS: The ADC values averaged over all patients in non-cancerous and malignant peripheral zone (PZ) tissues were 1.82 +/- 0.53 x 10(-3) (mean +/- SD) and 1.38 +/- 0.52 x 10(-3) mm(2)/second, respectively (P = 0.00045, N = 17, paired t-test). The ADC values were found to be higher in the non-cancerous PZ (1.88 +/- 0.48 x 10(-3)) than in healthy or benign prostatic hyperplasia central gland (BPH-CG) region (1.62 +/- 0.41 x 10(-3)). For the normal group, the mean values were 1.91 +/- 0.46 x 10(-3) and 1.63 +/- 0.30 x 10(-3) mm(2)/second for the PZ and CG, respectively (P = 0.011, N = 7). Significant overlap exists between individual values among all tissue types. Furthermore, ADC values for the same tissue type showed no statistically significant difference between the two subject groups. CONCLUSION: ADC is quantified in the prostate using DW-EPI. Values are lower in cancerous than in healthy PZ in patients, and in BPH-CG than PZ in volunteers.