Harry Bartlett

Modified RV Short Axis Series—A New Method for Cardiac MRI Measurement of Right Ventricular Volumes

PURPOSE The current standard image orientation employed in the MRI assessment of right ventricular volumes uses a series of short axis cine acquisitions located with respect to a horizontal long axis view with the first slice placed across the atrio-ventricular valve plane at end diastole. Inherent inaccuracies are encountered with the use of this image orientation due to difficulty in defining the tricuspid valve and the border between atrium and ventricle on the resultant images. Our experience indicates that because the tricuspid valve is usually not in-plane in the slice the atrio-ventricular margin is difficult to distinguish. This leads to inaccuracies in measurements at the base of the RV and miscalculation of the RV volume. The purpose of this study was to assess an alternative method of image orientation aimed at increasing the accuracy of RV volume measurements using current commercially available CMRI sequences. This technique, the modified RV short axis series, is oriented to the outflow tract of the right ventricle. METHOD We undertook a prospective study of 50 post cardiac transplant patients. A series of LV short axis multi-slice cine acquisition FIESTA images was acquired using the current standard technique. From this data set, LV and RV stroke volumes were derived on an Advantage Windows workstation using planimetry of the endocardial and epicardial borders in end systole and end diastole. Our new technique involved obtaining a set of multi-slice cine acquisition FIESTA images in a plane perpendicular to a line from the centre of the pulmonary valve to the apex of the RV. Planimetry of the RV was then performed and a stroke volume calculated using the same method of analysis. RV stroke volumes obtained from both techniques were compared with LV stroke volumes. Three operators independently derived RV data sets. RESULTS On the images acquired with the new technique, the tricuspid valve was easier to define leading to more accurate and reproducible planimetry of ventricular borders. RV stroke volumes calculated from the new method showed better agreement with LV stroke volumes than with the current method. These results were consistent across the three operators. CONCLUSIONS This new method improves visualisation of the tricuspid valve and makes analysis easier and less prone to operator error than the current standard technique for MRI assessment of RV volumes.

Determinants of in-hospital and long-term surgical outcomes after repair of postinfarction ventricular septal rupture

OBJECTIVES Surgical repair of post-myocardial infarction ventricular septal rupture is challenging with reported early mortality being substantial. In addition, congestive cardiac failure and ventricular tachyarrhythmia frequently occur long term after the operation, although frequency and predictive factors of these events have been poorly identified. METHODS A consecutive series of 68 patients who underwent repair of postinfarction ventricular septal rupture by 14 surgeons between 1988 and 2007 was studied. Fifty-eight (85%) patients underwent repair in an urgent setting (<48 hours after diagnosis). Coronary artery bypass grafting was concomitantly performed in 48 (71%) patients. Mean follow-up period was 9.2 +/- 4.9 years. RESULTS Thirty-day mortality was 35%, with previous myocardial infarction, previous cardiac surgery, preoperative left ventricular ejection fraction less than 40%, and urgent surgery being independent risk factors. Actuarial survival of 30-day survivors was 88% at 5 years, 73% at 10 years, and 51% at 15 years. Actuarial freedom from congestive cardiac failure and ventricular tachyarrhythmia was 70% and 85% at 5 years, 54% and 71% at 10 years, and 28% and 61% at 15 years, respectively. Independent predictors for congestive cardiac failure included hypertension, posterior septal rupture, residual interventricular communication, and preoperative left ventricular ejection fraction less than 40%, whereas concomitant ventricular aneurysmectomy and preoperative occlusion of the left anterior descending artery were independent predictors of ventricular tachyarrhythmia. CONCLUSIONS Long-term outcomes after surgical repair of postinfarction ventricular septal rupture was favorable, despite infrequent exposure by individual surgeons to the pathologic features, indicating that an aggressive surgical approach is warranted. Predictors of congestive cardiac failure and ventricular arrhythmia long term varied.

Relationships between HMG‐CoA reductase inhibitors (statin) use and strength, balance and falls in older people

To investigate associations between HMG‐CoA reductase inhibitor (statin) use and muscle strength, balance, mobility and falls in older people.

Investigating Cube Attacks on the Authenticated Encryption Stream Cipher MORUS

The cube attack is an algebraic attack that allows an adversary to extract low degree polynomial equations from the targeted cryptographic primitive. This work applies the cube attack to a reduced round version of ACORN , a candidate cipher design in the CAESAR cryptographic competition. The cube attack on 477 initialization rounds of ACORN can recover the 128 bit key with a total attack complexity of about 2 35 . We have also shown that linear equations relating the initial state of the full version of ACORN can be easily generated which can lead to state recovery attack with an attack complexity of about 2 72.8 .

Impact of pain location, organ system and treating speciality on timely delivery of analgesia in emergency departments

Objective: This retrospective, observational cohort study investigated whether the clinical features of a patients pain, including anatomical location, organ system and likely treating speciality, impact on the delivery of analgesia within 30 min in EDs.

CHURNs: Freshness Assurance for Humans

We present CHURNs, a method for providing freshness and authentication assurances to human users. In computer-to-computer protocols, it has long been accepted that assurances of freshness such as random nonces are required to prevent replay attacks. Typically, no such assurance of freshness is presented to a human in a human-and-computer protocol. A Computer–HUman Recognisable Nonce (CHURN) is a computer-aided random sequence that the human has a measure of control over and input into. Our approach overcomes limitations such as ‘humans cannot do random’ and that humans will follow the easiest path. Our findings show that CHURNs are significantly more random than values produced by unaided humans; that humans may be used as a second source of randomness, and we give measurements as to how much randomness can be gained from humans using our approach; and that our CHURN-generator makes the user feel more in control, thus removing the need for complete trust in devices and underlying protocols. We give an example of how a CHURN may be used to provide assurances of freshness and authentication for humans in a widely used protocol.

Slide attacks on the Sfinks stream cipher

Sfinks is a shift register based stream cipher designed for hardware implementation and submitted to the eSTREAM project. In this paper, we analyse the initialisation process of Sfinks. We demonstrate a slid property of the loaded state of the Sfinks cipher, where multiple key-IV pairs may produce phase shifted keystream sequences. The state update functions of both the initialisation process and keystream generation and also the pattern of the padding affect generation of the slid pairs.

Weaknesses in the Initialisation Process of the Common Scrambling Algorithm Stream Cipher

The Common Scrambling Algorithm Stream Cipher (CSA-SC) is a shift register based stream cipher designed to encrypt digital video broadcast. CSA-SC produces a pseudo-random binary sequence that is used to mask the contents of the transmission. In this paper, we analyse the initialisation process of the CSA-SC keystream generator and demonstrate weaknesses which lead to state convergence, slid pairs and shifted keystreams. As a result, the cipher may be vulnerable to distinguishing attacks, time-memory-data trade-off attacks or slide attacks.

A General Model for MAC Generation Using Direct Injection

This paper presents a model for generating a MAC tag by injecting the input message directly into the internal state of a nonlinear filter generator. This model generalises a similar model for unkeyed hash functions proposed by Nakano et al. We develop a matrix representation for the accumulation phase of our model and use it to analyse the security of the model against man-in-the-middle forgery attacks based on collisions in the final register contents. The results of this analysis show that some conclusions of Nakano et al regarding the security of their model are incorrect. We also use our results to comment on several recent MAC proposals which can be considered as instances of our model and specify choices of options within the model which should prevent the type of forgery discussed here. In particular, suitable initialisation of the register and active use of a secure nonlinear filter will prevent an attacker from finding a collision in the final register contents which could result in a forged MAC.

Algebraic analysis of the SSS stream cipher

Both the SSS and SOBER-t32 stream cipher designs use a single word-based shift register and a nonlinear filter function to produce keystream. In this paper we show that the algebraic attack method previously applied to SOBER-t32 is prevented from succeeding on SSS by the use of the keydependent substitution box (SBox) in the nonlinear filter of SSS. Additional assumptions and modifications to the SSS cipher in an attempt to enable algebraic analysis result in other difficulties that also render the algebraic attack infeasible. Based on these results, we conclude that a well-chosen key-dependent substitution box used in the nonlinear filter of the stream cipher provides resistance against such algebraic attacks.