Table of contents

Physics in Medicine and Biology (PMB) is a journal that originated in the UK but is now rightly regarded as one of the pre-eminent international journals for the publication of material coming within its remit. It is 50 years old and its maturity is an outcome of the consistent support of high performing authors, a supportive and professional publishing house, dedicated referees, many vigorous and conscientious editorial boards and the collective input of the 10 previous Editors as listed in his incoming editorial (January 2000 issue) by the retiring Editor, Professor Alun Beddoe.

The scientific climate and it associated publication modus operandi in the 1950s was very different from that at the current time and the journal has evolved to reflect this. Hence today the scope of content is somewhat broader, the size of the journal is vastly greater, the whole publication process is slicker and more efficient and a paper in PMB is highly prized by its authors and those who look to quality factors and impact.

The quality of the journal still relies on the voluntary labour and expertise of its busy international referees and Board members. For many years I have tried to place my own research material in PMB and encourage my teams to do likewise, not only acknowledging the prestige of the journal but also because of the extraordinarily fast turnaround time of all the processes without any loss of quality. This serves us very well and the publishing team are to be congratulated.

Some things seem to change more slowly or not at all, however. The prediction, when I started my research career, that books and journals would be dinosaurs by now has manifestly not come true and, whilst most of us are addicted (and why not?) to the electronic ways of doing things that can be done by more traditional ways, PMB and a packet of reprints from time to time arriving by post still has a reassuring feel despite the fact that the papers have been `on-line' for a while before.

An incoming editor signals change and in turn this induces in some people expectation, hope of improvement and maybe radical revolution. Others cower and hope for stability, continuation of the same and as little outward sign of change as possible. So I should like to signal that I hope to satisfy both camps. The Editor-in-Chief is primarily a guardian of the journal and should change nothing that does not need changing. Maintaining a standard at the same level is a valuable achievement in itself. This is no different from taking on any other leadership role such as in a team or department. One has to lead by consensus and with respect for the position. Conversely there are things I would like to see improved (otherwise I should not have been hired) and I commit to attempting these but in a spirit of cooperation with the Board, the publisher (IOP), IPEM and the readership. Any other approach would be doomed anyway.

So, what would I like to see changed? Dare I say anything too strongly upfront? Like Alun six years ago I would like there to be more debate via correspondence but this depends on the readers to do more writing along these lines. Personally I feel PMB, like many journals, has developed to the point where most readers sadly can understand only a small fraction of its contents. I have talked to older readers who said they regularly used to read all or half of the journal. Now many of us can manage only the papers in our specialty. Yet this is somewhat inevitable as medical physics has progressed from a fledgling science to the vast activity it is today, topics have become deeply complicated and we cannot and should not reverse the clock. To address this, I would like to see authors provide some form of `intelligible lay-scientific summary' of their paper as a condition of its publication. I think readers would then enjoy reading all, not just some, of these and maybe become attracted to other areas than the ones in which they currently work.

I would like to see the voluntary and anonymous publication of selected referees' comments `tailing' (some) published papers. They would need to be brief, specifically crafted for the purpose, of substantial impact, avoid excess length or editorial detail and above all be polite and constructive. I think this would bring more life into what (for all journals not just PMB) is a somewhat clinically manicured format. Issues requiring detailed response or countering would need to proceed as usual to their own peer-reviewed papers but maybe a quarter page of a reviewer's carefully submitted footnotes might be interesting. It might also be nice to have stated for each paper the referees' expertise and their scientific background. Maintaining referee anonymity would be an undebateable pre-requisite. I don't know if this would be feasible, popular or even generally desirable but I shall ask the Board for their views.

We live in an age when publications serve more needs than the dissemination of knowledge. CVs, careers, future funding, university assessments and so on all depend on the production of a healthy list of peer-reviewed papers. This is also probably unstoppable and younger workers are growing up accepting it while (some) older ones may hark back to less cluttered times. So improving the impact of PMB has to be a goal. An obvious mechanism is just to cut the number of published papers and raise the acceptance standard. Yet this would be deeply unpopular given the above extra reasons to publish and that it is hard to believe PMB is currently publishing `substandard' material. The Board and I will have to address that.

Over the next few years the debate over e-journals versus paper journals, open access publication, and freedom or otherwise of the web will all impact on PMB. Only the day I wrote this I read that in a London lecture Bill Gates has predicted that in just ten years electronic flexipaper with wireless internet access will be able to find anything on the web including journals. Scientists anywhere and everywhere in the world, at home, in the office, on transport, or on the beach, will be able to read journals (if they want this facility that is); so will there be any need for PMB hardcopy? I think there will but many think otherwise. Times will change and we again need to manage the change for good.

I should like to thank the outgoing Editor and all those who have placed confidence in me that I will maintain the good, change and develop what needs to be so treated, contribute some fresh thoughts and serve with energy, dignity and patience.

An RF phased array applicator has been constructed for hyperthermia treatments in the intact breast. This RF phased array consists of four antennas mounted on a Lexan water tank, and geometric focusing is employed so that each antenna points in the direction of the intended target. The operating frequency for this phased array is 140 MHz. The RF array has been characterized both by electric field measurements in a water tank and by electric field simulations using the finite-element method. The finite-element simulations are performed with HFSS software, where the mesh defined for finite-element calculations includes the geometry of the tank enclosure and four end-loaded dipole antennas. The material properties of the water tank enclosure and the antennas are also included in each simulation. The results of the finite-element simulations are compared to the measured values for this configuration, and the results, which include the effects of amplitude shading and phase shifting, show that the electric field predicted by finite-element simulations is similar to the measured field. Simulations also show that the contributions from standing waves are significant, which is consistent with measurement results. Simulated electric field and bio-heat transfer results are also computed within a simple 3D breast model. Temperature simulations show that, although peak temperatures are generated outside the simulated tumour target, this RF phased array applicator is an effective device for regional hyperthermia in the intact breast.

The purpose of this study was to demonstrate that a commercially available cabinet x-ray system is capable of phase-contrast radiography (PC-R) and to evaluate the effect of different system parameters on the degree of edge enhancement. An acrylic plastic edge phantom was imaged at different tube potentials (25–60 kV) and in different geometries (variable object-to-detector distances, R₂, at a constant source-to-detector distance, R₁ + R₂). In addition, the effect of noise on the perceived edge enhancement was studied as a function of exposure time. Our results show that a modest degree of phase contrast can be achieved in an unmodified cabinet x-ray system. In addition, the particular system evaluated allowed low-noise PC-R images to be obtained with short (6 s or less) exposures. These results suggest that with appropriate geometric choices PC-R is already available to a wide range of research scientists for use in both small-animal and human-specimen experiments.

An adaptive prediction approach was developed to infer internal target position by external marker positions. First, a prediction model (or adaptive neural network) is developed to infer target position from its former positions. For both internal target and external marker motion, two networks with the same type are created. Next, a linear model is established to correlate the prediction errors of both neural networks. Based on this, the prediction error of an internal target position can be reconstructed by the linear combination of the prediction errors of the external markers. Finally, the next position of the internal target is estimated by the network and subsequently corrected by the reconstructed prediction error. In a similar way, future positions are inferred as their previous positions are predicted and corrected. This method was examined by clinical data. The results demonstrated that an improvement (10% on average) of correlation between predicted signal and real internal motion was achieved, in comparison with the correlation between external markers and internal target motion. Based on the clinical data (with correlation coefficient 0.75 on average) observed between external marker and internal target motions, a prediction error (23% on average) of internal target position was achieved. The preliminary results indicated that this method is helpful to improve the predictability of internal target motion with the additional information of external marker signals. A consistent correlation between external and internal signals is important for prediction accuracy.

Simultaneous near-infrared spectroscopy (NIRS) and magnetic resonance imaging (MRI) were used to investigate the correlation between tumour vascular oxygenation and tissue oxygen tension dynamics in rat breast 13762NF tumours with respect to hyperoxic gas breathing. NIRS directly detected global variations in the oxygenated haemoglobin concentration (Δ[HbO₂]) within tumours and oxygen tension (pO₂) maps were achieved using ¹⁹F MRI of the reporter molecule hexafluorobenzene. Multiple correlations were examined between rates and magnitudes of vascular (Δ[HbO₂]) and tissue (pO₂) responses. Significant correlations were found between response to oxygen and carbogen breathing using either modality. Comparison of results for the two methods showed a correlation between the vascular perfusion rate ratio and the mean pO₂ values (R² > 0.7). The initial rates of increase of Δ[HbO₂] and the slope of dynamic pO₂ response, d(pO₂)/dt, of well-oxygenated voxels in response to hyperoxic challenge were also correlated. These results demonstrate the feasibility of simultaneous measurements using NIRS and MRI. As expected, the rate of pO₂ response to oxygen is primarily dependent upon the well perfused rather than poorly perfused vasculature.

Blood flow and hypoxia are interrelated aspects of physiology that affect cancer treatment and response. Cu-PTSM and Cu-ATSM are related PET tracers for blood flow and hypoxia, and the ability to rapidly image both tracers in a single scan would bring several advantages over conventional single-tracer techniques. Using dynamic imaging with staggered injections, overlapping signals for multiple PET tracers may be recovered utilizing information from kinetics and radioactive decay. In this work, rapid dual-tracer PTSM+ATSM PET was simulated and tested as a function of injection delay, order and relative dose for several copper isotopes, and the results were compared relative to separate single-tracer data. Time-activity curves representing a broad range of tumour blood flow and hypoxia levels were simulated, and parallel dual-tracer compartment modelling was used to recover the signals for each tracer. The main results were tested further using a torso phantom simulation of PET tumour imaging. Using scans as short as 30 minutes, the dual-tracer method provided measures of blood flow and hypoxia similar to single-tracer imaging. The best performance was obtained by injecting PTSM first and using a somewhat higher dose for ATSM. Comparable results for different copper isotopes suggest that tracer kinetics with staggered injections play a more important role than radioactive decay in the signal separation process. Rapid PTSM+ATSM PET has excellent potential for characterizing both tumour blood flow and hypoxia in a single, fast scan, provided that technological hurdles related to algorithm development and routine use can be overcome.

Fully 3D PET data are often rebinned into 2D data sets in order to avoid computationally intensive fully 3D reconstruction. Then, conventional 2D reconstruction techniques are employed to obtain images from the rebinned data. In a common scenario, 2D filtered back projection (FBP) is applied to Fourier rebinned (FORE) data. This approach is suboptimal because FBP is based on an idealized mathematical model of the data and cannot account for the statistical structure of data and noise. FORE data contain some blur in all three dimensions in comparison to conventional 2D PET data. In this work, we propose methods for approximating this blur in the sinogram domain due to FORE through its point spread function (PSF). We also explore simple methods for deconvolving the rebinned data with this PSF to restore it to a more ideal state prior to FBP. Our results show that deconvolution of the approximate transaxial PSF yields no improvement. When low image noise levels are required for detection tasks, the deconvolution of the axial PSF does not provide adequate resolution or quantitative benefits to justify its application. When accurate quantitation is required and higher noise levels are acceptable, the deconvolution of the axial PSF leads to considerable gains (30%) in accuracy over conventional FORE+FBP at matched noise levels.

Model-based elastography is fraught with problems owing to the ill-posed nature of the inverse elasticity problem. To overcome this limitation, we have recently developed a novel inversion scheme that incorporates a priori information concerning the mechanical properties of the underlying tissue structures, and the variance incurred during displacement estimation in the modulus image reconstruction process. The information was procured by employing standard strain imaging methodology, and introduced in the reconstruction process through the generalized Tikhonov approach. In this paper, we report the results of experiments conducted on gelatin phantoms to evaluate the performance of modulus elastograms computed with the generalized Tikhonov (GTK) estimation criterion relative to those computed by employing the un-weighted least-squares estimation criterion, the weighted least-squares estimation criterion and the standard Tikhonov method (i.e., the generalized Tikhonov method with no modulus prior). The results indicate that modulus elastograms computed with the generalized Tikhonov approach had superior elastographic contrast discrimination and contrast recovery. In addition, image reconstruction was more resilient to structural decorrelation noise when additional constraints were imposed on the reconstruction process through the GTK method.

Cryogen spray cooling (CSC) is a technique employed to reduce the risk of epidermal damage during dermatologic laser surgery. However, while CSC protects the epidermis from non-specific thermal damage, it might reduce the effective fluence reaching the target chromophore due to scattering of light by the spray droplets and subsequent water condensation/freezing on the skin surface. The objective of this work was to study the effect of ambient humidity (ω) on light transmittance during CSC. An integrating sphere was employed to measure the dynamics of light transmittance through a deformable agar phantom during CSC. The study included two representative CSC spurt patterns studied using four ω: 57, 40, 20 and 12%. Results show that during CSC, as ω increased, light transmittance decreased. For the highest humidity level (57%) studied, light transmittance reached a minimum of 55% approximately 30 ms after spurt termination. In a controlled environment with ω = 12%, light transmittance reached a minimum of 87% approximately 30 ms after spurt termination. The reduced light transmittance immediately after spurt termination was most likely because of scattering of light caused by condensation of water vapour due to aggressive cooling of ambient air in the wake of the cryogen spurt.

The purpose of the study was to compare algorithms of four methods (plus two modifications) for spectrophotometric haemoglobin saturation measurements. Comparison was made in tissue phantoms basically consisting of a phosphate buffer, Intralipid and blood, allowing samples to be taken for reference measurements. Three experimental series were made. In experiment A (eight phantoms) we used the Knoefel method and measured specific extinction coefficients with a reflection spectrophotometer. In experiment B (six phantoms) the fully oxygenated phantoms were gradually deoxygenated with baker's yeast, and simultaneous measurements were made with our spectrophotometer and with a reference oxymeter (ABL-605) in 3 min intervals. For each spectrophotometric measurement haemoglobin saturation was calculated with all algorithms and modifications, and compared with reference. In experiment C (11 phantoms) we evaluated the ability of a modification of the Knoefel method to measure haemoglobin concentration in absolute quantities using extinction coefficients from experiment A.

Results. Experiment A: with the Knoefel method extinction coefficients (±SD) for oxyhaemoglobin at 553.04 and 573.75 nm were 1.117 (±0.0396) ODmM⁻¹ and 1.680 (± 0.0815) ODmM⁻¹, respectively, and for deoxyhaemoglobin 1.205 (± 0.0514) ODmM⁻¹ and 0.953 (±0.0487) ODmM⁻¹, respectively. Experiment B: high correlation with the reference was found in all methods (r = 0.94–0.97). However, agreement varied from evidently wrong in method 3 and the original method 4 (e.g. saturation above 160%) to high agreement in method 2 as well as the modifications of methods 1 and 4, where oxygen dissociation curves were close to the reference method. Experiment C: with the modified Knoefel method the mean haemoglobin concentration difference from reference was 8.3% and the correlation was high (r = 0.91).

We conclude that method 2 and the modifications of 1 and 4 were superior to the others, but depended on known values in the same or similar phantoms. The original method 1 was independent of results from the tissue phantoms, but agreement was slightly poorer. Method 3 and the original method 4 could not be recommended. The ability of the modified method 1 to measure haemoglobin concentration is promising, but needs further development.

Extraction of foetal ECG that is embedded in the maternal ECG is a challenging problem. This paper presents a combined system to extract foetal ECG from maternal abdominal ECG. The system uses a combination of singular value decomposition (SVD) and a neuro-fuzzy inference system. The SVD is used to construct two reference signals, while the fuzzy system is used as an adaptive canceller. The algorithm is applied on synthetic as well as real data and the results are presented. In addition, the paper presents an example of using the same system as a noise removal tool.

Vortex currents may be of importance in the early diagnosis of myocardial infarction caused by an occlusion of a coronary artery. We investigated the influence of a passive vortex current distribution, modelled by different conductivities in a hollow cylinder, on the localization error and on the signal strength in both the magnetocardiogram and the electrocardiogram. The hollow cylinder was mounted in a realistically shaped physical torso phantom. A platinum dipole was inserted into the cylinder. The compartment boundaries were modelled with two special ionic exchange membranes. The conductivity ratio of the cylinder compartment to the torso compartment was varied from 0.25 to 100. We compared the simultaneously measured magnetic and electric signal strengths as a function of this conductivity ratio. We found that an increasing conductivity ratio causes only a slight increase (about 19%) of the magnetic signal strength but a strong decrease (about 81%) of the electric signal strength. Using a homogeneous torso model, the dipole localization errors were, depending on the conductivity ratio, up to 16 mm. In conclusion, passive vortex currents might partially explain the differences between magnetocardiographic and electrocardiographic recordings observed both experimentally and clinically.

A model is presented for serial, critical element complication mechanisms for irradiated volumes from length scales of a few millimetres up to the entire organ. The central element of the model is the description of radiation complication as the failure of a dynamic repair process. The nature of the repair process is seen as reestablishing the structural organization of the tissue, rather than mere replenishment of lost cells. The interactions between the cells, such as migration, involved in the repair process are assumed to have finite ranges, which limits the repair capacity and is the defining property of a finite-sized reconstruction unit. Since the details of the repair processes are largely unknown, the development aims to make the most general assumptions about them. The model employs analogies and methods from thermodynamics and statistical physics. An explicit analytical form of the dose response of the reconstruction unit for total, partial and inhomogeneous irradiation is derived. The use of the model is demonstrated with data from animal spinal cord experiments and clinical data about heart, lung and rectum. The three-parameter model lends a new perspective to the equivalent uniform dose formalism and the established serial and parallel complication models. Its implications for dose optimization are discussed.

To find the properties in the oscillatory components of the cutaneous blood flow on the successful free flap, a wavelet transform was applied to the laser Doppler flowmetry (LDF) signals which were measured simultaneously on the surfaces of the free latissimus dorsi myocutaneous flap and on the adjacent intact skin of the healthy limb, of 18 patients. The frequency interval from 0.0095 to 1.6 Hz was examined and was divided into five subintervals (I: 0.0095–0.021 Hz; II: 0.021–0.052 Hz; III: 0.052–0.145 Hz; IV: 0.145–0.6 Hz and V: 0.6–1.6 Hz) corresponding to endothelial metabolic, neurogenic, myogenic, respiratory and cardiac origins. The average amplitude and total power in the frequency range 0.0095–1.6 Hz as well as within subintervals I, II, IV and V were significantly lower for signals measured on the free flap than those obtained in the healthy limb. However in interval III, they were significantly higher. The normalized spectral amplitude and power in the free flap were significantly lower in only two intervals, I and II, yet in interval III they were significantly higher; no statistical significance was observed in intervals IV and V. The distinctive finding made in this study, aside from the decrease of endothelial metabolic processes and sympathetic control, was the significant increase of myogenic activity in the free flap. It is hoped that this work will contribute towards knowledge on blood circulation in free flaps and make the monitoring by LDF more reliable.

Previous treatment of cerebrospinal fluid (CSF) malignancies by intrathecal administration of ¹³¹I-radiolabelled monoclonal antibodies has led to the assumption that more healthy tissue will be spared when a pure beta-emitter such as ⁹⁰Y replaces ¹³¹I. The purpose of this study is to compare and quantitatively evaluate the dose distribution from ⁹⁰Y to the CSF space and its surrounding spinal structures to ¹³¹I. A 3D digital phantom of a section of the T-spine was constructed from the visible human project series of images which included the spinal cord, central canal, subarachnoid space, pia mater, arachnoid, dura mater, vertebral bone marrow and intervertebral disc. Monte Carlo N-particle (MCNP4C) was used to model the ⁹⁰Y and ¹³¹I radiation distribution. Images of the CSF compartment were convolved with the radiation distribution to determine the dose within the subarachnoid space and surrounding tissues. ⁹⁰Y appears to be a suitable radionuclide in the treatment of central nervous system (CNS) malignancies when attached to mAb's and the dose distribution would be confined largely within the vertebral foramen. This choice may offer favourable dose improvement to the subarachnoid and surface of spinal cord over ¹³¹I in such an application.

The potential for systematic errors in radiotherapy of a breathing patient is considered using the statistical model of Bortfeld et al (2002 Phys. Med. Biol.47 2203–20). It is shown that although averaging over 30 fractions does result in a narrow Gaussian distribution of errors, as predicted by the central limit theorem, the fact that one or a few samples of the breathing patient's motion distribution are used for treatment planning (in contrast to the many treatment fractions that are likely to be delivered) may result in a much larger error with a systematic component. The error distribution may be particularly large if a scan at breath-hold is used for planning.

The injection of microspheres into the blood stream has been a common method to measure the spatial distribution of blood flow (perfusion). A technique to conduct this kind of measurement in small animal organs is presented using silver-coated microspheres with a diameter of 16 µm and high-resolution computed tomography (microCT) to detect individual microspheres. Phantom experiments demonstrate the detectability of individual spheres. The distribution of microspheres within a rat heart is given as an example. Using non-destructive, three-dimensional imaging for microsphere detection avoids the cumbersome dissection of the organ into samples or slices and their subsequent registration. The detection of individual spheres allows high-resolution measurements of perfusion and arbitrary definition of regions of interest. These, in turn, allow for accurate statistical analysis of perfusion such as relative dispersion curves.

Kodak recently introduced new packaging for its X-Omat V verification film, including a label on the exterior of the packet. Patient images taken using the film in an image intensification cassette showed artefacts which appeared to be related to the label. Investigation showed the effect was only observed in conditions of high-Z build-up or backscatter or when the film was used without additional backscatter. The label provides extra build up when in front of the film and an increase in optical density of up to 0.04 units. When the label is on the rear of the film it absorbs backscattered particles, causing a decrease in optical density. It is concluded that X-Omat V film packets with labels are unsuitable for use in imaging cassettes unless they are used in conditions of low-Z build-up. Alternatively the film must be removed from the labelled envelope if it is to be used in high-Z build-up conditions.