Factors affecting performance of fetal blood T2 measurements for noninvasive estimation of oxygen saturation

PURPOSE

To ultimately make accurate and precise fetal noninvasive oxygen saturation (sO2 ) measurements by T2 -prepared bSSFP more widely available by systematically assessing error sources in order to potentially reduce perinatal mortality in cardiovascular malformations and fetal growth restriction.

METHODS

T2 -prepared bSSFP data were acquired in phantoms; in flowing blood in adults in the superior sagittal sinus, ascending and descending aorta, and main pulmonary artery; and in the fetal descending aorta and umbilical vein. T2 was assessed in relation to T2 two- or three-parameter curve-fitting techniques, SSFP readout, refocusing time delay (τ), constant and pulsatile blood flow, and impact of T1 recovery. Further, fetal T2 and sO2 variability were quantified in the descending aorta and umbilical vein in healthy fetuses and fetuses with cardiovascular malformation (gestational weeks 32-38).

RESULTS

In phantoms, three-parameter fitting was accurate irrespective of phase FOV (<4 ms; i.e., <2%), and T2 was overestimated (up to 23 ms/10%; p = 0.001) beyond ±30 Hz off-resonance. In the adult aorta, T2 was underestimated during higher blood flow velocities and pulsatility for τ = 16 ms (-41 ms/-17%; p = 0.008). In fetuses, two-parameter fitting overestimated T2 compared with three-parameter fitting (+33 ms/+18%; p = 0.03). T2 variability was 18 ms/15% in the fetal descending aorta and 28 ms/14% in the umbilical vein. The resulting estimated sO2 variability was ∼10% (15% of sO2 value) in the fetal descending aorta.

CONCLUSIONS

Errors due to T2 -fitting techniques, off-resonance, flow velocity, and insufficient T1 recovery between image acquisitions could be mitigated by using three-parameter fitting with included saturation-prepared images approximating infinite T2 -preparation time, adequate shimming covering the fetus and placenta, and by modifying acquisition parameters. Variability in fetal blood T2 and sO2 , however, indicate that it is currently not feasible to use these methods for prediction of disease.

A numerical human brain phantom for dynamic glucose-enhanced (DGE) MRI: On the influence of head motion at 3T

PURPOSE

Dynamic glucose-enhanced (DGE) MRI relates to a group of exchange-based MRI techniques where the uptake of glucose analogues is studied dynamically. However, motion artifacts can be mistaken for true DGE effects, while motion correction may alter true signal effects. The aim was to design a numerical human brain phantom to simulate a realistic DGE MRI protocol at 3T that can be used to assess the influence of head movement on the signal before and after retrospective motion correction.

METHODS

MPRAGE data from a tumor patient were used to simulate dynamic Z-spectra under the influence of motion. The DGE responses for different tissue types were simulated, creating a ground truth. Rigid head movement patterns were applied as well as physiological dilatation and pulsation of the lateral ventricles and head-motion-induced B0 -changes in presence of first-order shimming. The effect of retrospective motion correction was evaluated.

RESULTS

Motion artifacts similar to those previously reported for in vivo DGE data could be reproduced. Head movement of 1 mm translation and 1.5 degrees rotation led to a pseudo-DGE effect on the order of 1% signal change. B0 effects due to head motion altered DGE changes due to a shift in the water saturation spectrum. Pseudo DGE effects were partly reduced or enhanced by rigid motion correction depending on tissue location.

CONCLUSION

DGE MRI studies can be corrupted by motion artifacts. Designing post-processing methods using retrospective motion correction including B0 correction will be crucial for clinical implementation. The proposed phantom should be useful for evaluation and optimization of such techniques.

Fetal 3D cardiovascular cine image acquisition using radial sampling and compressed sensing

PURPOSE

To explore a fetal 3D cardiovascular cine acquisition using a radial image acquisition and compressed-sensing reconstruction and compare image quality and scan time with conventional multislice 2D imaging.

METHODS

Volumetric fetal cardiac data were acquired in 26 volunteers using a radial 3D balanced SSFP pulse sequence. Cardiac gating was performed using a Doppler ultrasound device. Images were reconstructed using a parallel-imaging and compressed-sensing algorithm. Multiplanar reformatting to standard cardiac views was performed before image analysis. Clinical 2D images were used for comparison. Qualitative and quantitative image evaluation were performed by two experienced observers (scale: 1-4). Volumes, mass, and function were assessed.

RESULTS

Average scan time for the 3D imaging was 6 min, including one localizer. A 2D imaging stack covering the entire heart including localizer sequences took at least 6.5 min, depending on planning complexity. The 3D acquisition was successful in 7 of 26 subjects (27%). Overall image contrast and perceived resolution were lower in the 3D images. Nonetheless, the 3D images had, on average, a moderate cardiac diagnostic quality (median [range]: 3 [1-4]). Standard clinical 2D acquisitions had a high cardiac diagnostic quality (median [range]: 4 [3, 4]). Cardiac measurements were not different between 2D and 3D images (all p > 0.16).

CONCLUSION

The presented free-breathing whole-heart fetal 3D radial cine MRI acquisition and reconstruction method enables retrospective visualization of all cardiac views while keeping examination times short. This proof-of-concept work produced images with diagnostic quality, while at the same time reducing the planning complexity to a single localizer.

MR-compatible optical microscope for in-situ dual-mode MR-optical microscopy

We present the development of a dual-mode imaging platform that combines optical microscopy with magnetic resonance microscopy. Our microscope is designed to operate inside a 9.4T small animal scanner with the option to use a 72mm bore animal RF coil or different integrated linear micro coils. With a design that minimizes the magnetic distortions near the sample, we achieved a field inhomogeneity of 19 ppb RMS. We further integrated a waveguide in the optical layout for the electromagnetic shielding of the camera, which minimizes the noise increase in the MR and optical images below practical relevance. The optical layout uses an adaptive lens for focusing, 2 × 2 modular combinations of objectives with 0.6mm to 2.3mm field of view and 4 configurable RGBW illumination channels and achieves a plano-apochromatic optical aberration correction with 0.6μm to 2.3μm resolution. We present the design, implementation and characterization of the prototype including the general optical and MR-compatible design strategies, a knife-edge optical characterization and different concurrent imaging demonstrations.

Assessment of Amide proton transfer weighted (APTw) MRI for pre-surgical prediction of final diagnosis in gliomas

PURPOSE

Radiological assessment of primary brain neoplasms, both high (HGG) and low grade tumors (LGG), based on contrast-enhancement alone can be inaccurate. We evaluated the radiological value of amide proton transfer weighted (APTw) MRI as an imaging complement for pre-surgical radiological diagnosis of brain tumors.

METHODS

Twenty-six patients were evaluated prospectively; (22 males, 4 females, mean age 55 years, range 26-76 years) underwent MRI at 3T using T1-MPRAGE pre- and post-contrast administration, conventional T2w, FLAIR, and APTw imaging pre-surgically for suspected primary/secondary brain tumor. Assessment of the additional value of APTw imaging compared to conventional MRI for correct pre-surgical brain tumor diagnosis. The initial radiological pre-operative diagnosis was based on the conventional contrast-enhanced MR images. The range, minimum, maximum, and mean APTw signals were evaluated. Conventional normality testing was performed; with boxplots/outliers/skewness/kurtosis and a Shapiro-Wilk's test. Mann-Whitney U for analysis of significance for mean/max/min and range APTw signal. A logistic regression model was constructed for mean, max, range and Receiver Operating Characteristic (ROC) curves calculated for individual and combined APTw signals.

RESULTS

Conventional radiological diagnosis prior to surgery/biopsy was HGG (8 patients), LGG (12 patients), and metastasis (6 patients). Using the mean and maximum: APTw signal would have changed the pre-operative evaluation the diagnosis in 8 of 22 patients (two LGGs excluded, two METs excluded). Using a cut off value of >2.0% for mean APTw signal integral, 4 of the 12 radiologically suspected LGG would have been diagnosed as high grade glioma, which was confirmed by histopathological diagnosis. APTw mean of >2.0% and max >2.48% outperformed four separate clinical radiological assessments of tumor type, P-values = .004 and = .002, respectively.

CONCLUSIONS

Using APTw-images as part of the daily clinical pre-operative radiological evaluation may improve diagnostic precision in differentiating LGGs from HGGs, with potential improvement of patient management and treatment.

Validation and reproducibility of cardiovascular 4D-flow MRI from two vendors using 2 × 2 parallel imaging acceleration in pulsatile flow phantom and in vivo with and without respiratory gating

Background

4D-flow magnetic resonance imaging (MRI) is increasingly used.

Purpose

To validate 4D-flow sequences in phantom and in vivo, comparing volume flow and kinetic energy (KE) head-to-head, with and without respiratory gating.

Material and Methods

Achieva dStream (Philips Healthcare) and MAGNETOM Aera (Siemens Healthcare) 1.5-T scanners were used. Phantom validation measured pulsatile, three-dimensional flow with 4D-flow MRI and laser particle imaging velocimetry (PIV) as reference standard. Ten healthy participants underwent three cardiac MRI examinations each, consisting of cine-imaging, 2D-flow (aorta, pulmonary artery), and 2 × 2 accelerated 4D-flow with (Resp+) and without (Resp−) respiratory gating. Examinations were acquired consecutively on both scanners and one examination repeated within two weeks. Volume flow in the great vessels was compared between 2D- and 4D-flow. KE were calculated for all time phases and voxels in the left ventricle.

Results

Phantom results showed high accuracy and precision for both scanners. In vivo, higher accuracy and precision (P < 0.001) was found for volume flow for the Aera prototype with Resp+ (–3.7 ± 10.4 mL, r = 0.89) compared to the Achieva product sequence (–17.8 ± 18.6 mL, r = 0.56). 4D-flow Resp− on Aera had somewhat larger bias (–9.3 ± 9.6 mL, r = 0.90) compared to Resp+ (P = 0.005). KE measurements showed larger differences between scanners on the same day compared to the same scanner at different days.

Conclusion

Sequence-specific in vivo validation of 4D-flow is needed before clinical use. 4D-flow with the Aera prototype sequence with a clinically acceptable acquisition time (<10 min) showed acceptable bias in healthy controls to be considered for clinical use. Intra-individual KE comparisons should use the same sequence.

Self-gated fetal cardiac MRI with tiny golden angle iGRASP: A feasibility study

PURPOSE

To develop and assess a technique for self-gated fetal cardiac cine magnetic resonance imaging (MRI) using tiny golden angle radial sampling combined with iGRASP (iterative Golden-angle RAdial Sparse Parallel) for accelerated acquisition based on parallel imaging and compressed sensing.

MATERIALS AND METHODS

Fetal cardiac data were acquired from five volunteers in gestational week 29-37 at 1.5T using tiny golden angles for eddy currents reduction. The acquired multicoil radial projections were input to a principal component analysis-based compression stage. The cardiac self-gating (CSG) signal for cardiac gating was extracted from the acquired radial projections and the iGRASP reconstruction procedure was applied. In all acquisitions, a total of 4000 radial spokes were acquired within a breath-hold of less than 15 seconds using a balanced steady-state free precession pulse sequence. The images were qualitatively compared by two independent observers (on a scale of 1-4) to a single midventricular cine image from metric optimized gating (MOG) and real-time acquisitions.

RESULTS

For iGRASP and MOG images, good overall image quality (2.8 ± 0.4 and 2.6 ± 1.3, respectively, for observer 1; 3.6 ± 0.5 and 3.4 ± 0.9, respectively, for observer 2) and cardiac diagnostic quality (3.8 ± 0.4 and 3.4 ± 0.9, respectively, for observer 1; 3.6 ± 0.5 and 3.6 ± 0.9, respectively, for observer 2) were obtained, with visualized myocardial thickening over the cardiac cycle and well-defined myocardial borders to ventricular lumen and liver/lung tissue. For iGRASP, MOG, and real time, left ventricular lumen diameter (14.1 ± 2.2 mm, 14.2 ± 1.9 mm, 14.7 ± 1.1 mm, respectively) and wall thickness (2.7 ± 0.3 mm, 2.6 ± 0.3 mm, 3.0 ± 0.4, respectively) showed agreement and no statistically significant difference was found (all P > 0.05). Images with iGRASP tended to have higher overall image quality scores compared with MOG and particularly real-time images, albeit not statistically significant in this feasibility study (P > 0.99 and P = 0.12, respectively).

CONCLUSION

Fetal cardiac cine MRI can be performed with iGRASP using tiny golden angles and CSG. Comparison with other fetal cardiac cine MRI methods showed that the proposed method produces high-quality fetal cardiac reconstructions.

LEVEL OF EVIDENCE

2 Technical Efficacy: Stage 1 J. MAGN. RESON. IMAGING 2017;46:207-217.

Performance evaluation of matrix gradient coils

OBJECTIVE

In this paper, we present a new performance measure of a matrix coil (also known as multi-coil) from the perspective of efficient, local, non-linear encoding without explicitly considering target encoding fields.

MATERIALS AND METHODS

An optimization problem based on a joint optimization for the non-linear encoding fields is formulated. Based on the derived objective function, a figure of merit of a matrix coil is defined, which is a generalization of a previously known resistive figure of merit for traditional gradient coils.

RESULTS

A cylindrical matrix coil design with a high number of elements is used to illustrate the proposed performance measure. The results are analyzed to reveal novel features of matrix coil designs, which allowed us to optimize coil parameters, such as number of coil elements. A comparison to a scaled, existing multi-coil is also provided to demonstrate the use of the proposed performance parameter.

CONCLUSIONS

The assessment of a matrix gradient coil profits from using a single performance parameter that takes the local encoding performance of the coil into account in relation to the dissipated power.

Single-shot imaging with higher-dimensional encoding using magnetic field monitoring and concomitant field correction

PURPOSE

PatLoc (Parallel Imaging Technique using Localized Gradients) accelerates imaging and introduces a resolution variation across the field-of-view. Higher-dimensional encoding employs more spatial encoding magnetic fields (SEMs) than the corresponding image dimensionality requires, e.g. by applying two quadratic and two linear spatial encoding magnetic fields to reconstruct a 2D image. Images acquired with higher-dimensional single-shot trajectories can exhibit strong artifacts and geometric distortions. In this work, the source of these artifacts is analyzed and a reliable correction strategy is derived.

METHODS

A dynamic field camera was built for encoding field calibration. Concomitant fields of linear and nonlinear spatial encoding magnetic fields were analyzed. A combined basis consisting of spherical harmonics and concomitant terms was proposed and used for encoding field calibration and image reconstruction.

RESULTS

A good agreement between the analytical solution for the concomitant fields and the magnetic field simulations of the custom-built PatLoc SEM coil was observed. Substantial image quality improvements were obtained using a dynamic field camera for encoding field calibration combined with the proposed combined basis.

CONCLUSION

The importance of trajectory calibration for single-shot higher-dimensional encoding is demonstrated using the combined basis including spherical harmonics and concomitant terms, which treats the concomitant fields as an integral part of the encoding.

Single shot trajectory design for region-specific imaging using linear and nonlinear magnetic encoding fields

It has recently been demonstrated that nonlinear encoding fields result in a spatially varying resolution. This work develops an automated procedure to design single-shot trajectories that create a local resolution improvement in a region of interest. The technique is based on the design of optimized local k-space trajectories and can be applied to arbitrary hardware configurations that employ any number of linear and nonlinear encoding fields. The trajectories designed in this work are tested with the currently available hardware setup consisting of three standard linear gradients and two quadrupolar encoding fields generated from a custom-built gradient insert. A field camera is used to measure the actual encoding trajectories up to third-order terms, enabling accurate reconstructions of these demanding single-shot trajectories, although the eddy current and concomitant field terms of the gradient insert have not been completely characterized. The local resolution improvement is demonstrated in phantom and in vivo experiments.

Direct magnetic field estimation based on echo planar raw data

Gradient recalled echo echo planar imaging is widely used in functional magnetic resonance imaging. The fast data acquisition is, however, very sensitive to field inhomogeneities which manifest themselves as artifacts in the images. Typically used correction methods have the common deficit that the data for the correction are acquired only once at the beginning of the experiment, assuming the field inhomogeneity distribution B(0) does not change over the course of the experiment. In this paper, methods to extract the magnetic field distribution from the acquired k-space data or from the reconstructed phase image of a gradient echo planar sequence are compared and extended. A common derivation for the presented approaches provides a solid theoretical basis, enables a fair comparison and demonstrates the equivalence of the k-space and the image phase based approaches. The image phase analysis is extended here to calculate the local gradient in the readout direction and improvements are introduced to the echo shift analysis, referred to here as "k-space filtering analysis." The described methods are compared to experimentally acquired B(0) maps in phantoms and in vivo. The k-space filtering analysis presented in this work demonstrated to be the most sensitive method to detect field inhomogeneities.

[Reactive airway dysfunction syndrome: more flexible application of diagnostic criteria are important for occupational accident victims]

Reactive airway dysfunction syndrome (RADS), or Brooks syndrome, is a complication observed after inhalation of caustic or highly irritating substances. The diagnosis is based on a group of criteria which include the absence of prior respiratory disease. Strict application of these criteria could have a prejudicial effect for certain victims. Three serious cases of RADS were observed in workers who were exposed to massive inhalation of caustic substances. The products implicated (phosphoric oxychloride, titanium tetrachloride, and trichloroacetyl chloride) hydrolyze to hydrochloric acid when they come in contact with the airway mucosa. After an initial period of acute respiratory distress, the patients encountered serious difficulties in achieving an appropriate diagnosis, and in having their sequellae recognized as resulting from an occupational accident. The problem was that these patients had a history of cured allergic asthma or smoking-related COPD. The presence of prior respiratory disorders must not exclude the diagnosis of RADS. A prior respiratory disorder cannot be used as an argument to exclude such victims from indemnities for occupational accident sequelae.

[Severe ocular burns by calcium carbide in a speleologist: a case report]

A case of severe ocular burns in an amateur speleologist is reported. The explosion of his acetylene lamp caused the projection of calcium carbide particles, which induced burning of the cornea and conjunctiva in both eyes. He slowly recovered in several months. The pathophysiology of the burns, linked to the in situ production of lime, and their management are discussed.

[Occupational toxic exposure and the pregnant woman. 2: results of a prospective study of 100 pregnancies]

CONTEXT

Many women of childbearing age are occupationally exposed to chemicals and concerned with the ensuing risk when pregnant.

OBJECTIVES

To present the results of a prospective follow-up study of 100 pregnant women and to discuss them after a brief overview of the published data on this topic.

METHODS

Since January 1996 the Lyon Poison Center has been conducting a prospective follow-up of all request concerning pregnant women occupationally exposed to chemicals. A thorough evaluation of the hazards of the handled products and of the actual exposure at the workplace is done for each patient. A toxicological advice is given and the outcome of the pregnancy is followed-up.

RESULTS

One hundred pregnant women were included between January 1996 and December 2000. Based on the nature of the handled products, two groups have been identified: the first included 73 women exposed to organic solvents and the second 27 women exposed to miscellaneous. When the exposure was considered potentially hazardous for the pregnancy, either withdrawal from the workstation (19 cases), avoidance of certain activities (9 cases) or improvement of individual protective measures (29 cases) was recommended. In 43% of the cases, the occupational exposure was not considered hazardous to the outcome of the pregnancy. No increase of adverse outcome was identified: 4 miscarriages and 96 living births were observed, with 2 major malformations and 1 minor malformation.

CONCLUSION

Occupational exposure to chemicals was not found to affect adversely the outcome of these 100 pregnancies.

[Occupational toxic exposure in the pregnant woman. 1: principles fo individual risk assessment ]

CONTEXT

Many women of childbearing age are occupationally exposed to chemicals and concerned with the ensuing risk when pregnant.

OBJECTIVES

To describe the principles of individual risk assessment to be applied in pregnant women or women wishing to become pregnant that are exposed to chemicals at the workplace.

METHOD

Each request for risk assessment is based on a comprehensive review of the hazards of the handled products together with a thorough evaluation of the actual exposure at the workplace. A toxicological advice is then written to the gynecologist or the general practitioner in charge of the patient. When the exposure is estimated to be hazardous for the pregnancy, either total withdrawal, avoidance of certain activities or improvements of individual protective devices are recommended. The outcome of the pregnancy is systematically followed-up.

CONCLUSION

An objective assessment of toxic risks in pregnant women exposed to chemicals at the workplace can be done. Thus, patients who must be withdrawn or benefit from improvements of their workstation can be selected.

[A "historical" case of lead poisoning via drinking water: diagnostic and therapeutic issues]

INTRODUCTION

It is likely that lead poisoning via drinking water is often overlooked because of its supposed rarity and nonspecific early symptoms, which result in delayed management.

EXEGESIS

One case of severe lead poisoning via drinking water is reported. The diagnosis was long missed and a particularly long chelating treatment was required. The clinical features included lead colic, a Burton's lead line, anemia, polyneuritis and arterial hypertension. Eighteen courses of calcium EDTA were required to obtain 'biological recovery'. The poisoning was linked to a very long water supply lead pipe and potomania secondary to alcohol withdrawal.

CONCLUSION

This case report illustrates how difficult the early recognition of lead poisoning can be, and underlines the need to inquire about a toxic aetiology, particularly via the environment, of otherwise unexplained pathological conditions.

[Respiratory distress in three newborns after mask disinfection with Endosporine. Probable role of glutaraldehyde]

BACKGROUND

Disinfectants for medical devices are uncommonly a cause of iatrogenic adverse effects. Nevertheless, when misused, they can induce severe complications. Three cases of acute respiratory distress in newborns probably induced by glutaraldehyde are reported.

CASE REPORTS

Three children born by Caesarean section between 8 and 19 May 1999 in the same hospital presented acute respiratory distress requiring hospitalization in the neonatal intensive care unit; one child was premature. The clinical appearance, which was initially normal, deteriorated with a respiratory distress in 30 to 60 minutes. Recovery was uneventful in all cases. The diagnosis considered was a hyaline membrane disease. The enquiry conducted after this cluster onset identified, as a main contributing factor, the disinfection procedure recently introduced in the surgical theater.

CONCLUSION

Review of toxicologic data on glutaraldehyde shows this is a highly irritating chemical for the respiratory tract, even at low concentrations. Clinical and radiologic features in these three neonates are compatible with a pulmonary sub-edema on an immature alveolar setting. The hypothesis proposed is that glutaraldehyde, the active ingredient of the biocidal formula used to disinfect the respiratory masks, was massively desorbed from the rubber and foam of which masks are made.

[Respiratory manifestations after exposure to sulfurous anhydride in wine-cellar workers: 6 case reports]

Sulfite treatment of wine [a process exploiting the biocidal and anti-oxidant properties of sulfur dioxide (SO2)] involves the use of liquified gas, aqueous solutions or bisulfites, i.e. the salts of sulfurous acid which slowly release SO2. This procedure can result in repeated exposures of operators to significant amounts of SO2. However, risks associated with the use of SO2 are greatly under-estimated by wine producers and wine-cellar workers. We report on 6 cases of respiratory symptoms attributable to SO2 identified during a survey of wine-cellars in the French Beaujolais district. Their pathogenesis is discussed after an overview of the occupational toxicology of SO2.

[Acute alveolitis after using a waterproofing aerosol: apropos of 2 cases]

INTRODUCTION

Waterproofing sprays for leather clothing have seldom been involved in severe accidents. In some circumstances, their pulmonary toxicity is marked, as shown by two case reports and a review of the literature.

EXEGESIS

Acute alveolitis is described in two young adults without previous respiratory illness, following the use of a waterproofing spray for leather clothing. Clinical features typical of a flu-like reaction (malaise, fever and chills) were associated with dyspnea and with hemoptysis in one patient. X-ray examination evidenced lesional edema which quickly resolved after symptomatic treatment. The toxic mechanism is debated, but experimental data and clinical findings suggest the causative role of recently introduced fluoropolymers.

CONCLUSIONS

Waterproofing sprays for leather clothing may induce severe respiratory illness after massive inhalation in confined area. Treatment is supportive.

Acute hexogen poisoning after occupational exposure

BACKGROUND

Hexogen (cyclonite, RDX) nitrate explosive is an infrequent cause of poisoning.

CASE REPORT

A 42-year-old man with no prior history of epilepsy experienced grand mal seizures after sieving fine hexogen (RDX) powder for four hours in an ammunition plant. Physical examination was normal on arrival at the emergency room but recurrent seizures occurred six hour after admission. EEG, CT scan and MRI were normal and the patient recovered uneventfully.

CONCLUSIONS

The available toxicological data on this rare occupational poisoning are reviewed.

Methaemoglobinaemia due to amyl nitrite inhalation: a case report

Methaemoglobinaemia is a potential toxic effect of aliphatic nitrites which are increasingly abused by male homosexuals and drug addicts because of marked vasodilating properties ('poppers'). In most instances, severe complications were described following the ingestion of large quantities of amyl, butyl or isobutyl nitrites. A deficiency in NADH-dependent haemoglobin reductase in some patients has been noted. This is the first report of symptomatic methaemoglobinaemia following the inhalation of amyl nitrite.