Neuroimages: Pretty cool or what?


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This short essay aims to discuss whether neuroimaging has taught us anything of relevance, which we would not have known already through patient studies. The discussion breaks the subject of neuroimaging into three fundamentally important areas for further questioning: What is neuroimaging? How does neuroimaging benefit patients and aid professionals in their quest toward providing effective neurological diagnoses and/or treatments? Furthermore, what are some of the implications for patients in a future where neuroimaging might reasonably be assumed as situated at the heart of neurological and neuropsychological investigation? The discussion ends with some modest critique and reflections in conclusion.

Neuroimaging

“Neuroimaging has revolutionized the study of behavioural neurology and cognitive neuroscience.” One might reply to Devinsky & D’Esposito (2004: p. 52) by asking an innocent sounding question, namely: Perhaps, but does the promise of only positives stemming from the advent of functional neuroimaging really outweigh any negatives for patients with neurological dysfunctions? Upon closer inspection of the above claim however, one might also decide that the two distinguished professors (of neurology, neurosurgery, psychiatry and neuroscience and psychology, respectively) may actually know precisely what is at stake by making such a bold sounding assertion. In addition, it would of course be quite advantageous if one could source some instances or scenarios where functional neuroimaging might indeed not be as useful as many belief it to be. However, a cursory glance at a few respected texts (e.g. Carlson, 2007; Carter, 1998; Devinsky & D’Esposito, 2004; Frith, 2007; Kalat, 2007; Kandel et al., 2000; Ramachandran, 1998) will not produce a single objection to these technologies, in fact, rather the opposite is true. The truth is that many hail neuroimaging as quite simply revolutionary.

In order to conduct a logical discussion on the subject at hand one might, quite reasonably, be expected to answer some fundamentally important questions, like say: What is neuroimaging? How does neuroimaging benefit patients and aid professionals in their quest toward providing effective neurological diagnoses and/or treatments? Finally, what are some of the implications for patients in a future where neuroimaging might reasonably be assumed as situated at the heart of neurological and neuropsychological investigation?

What is neuroimaging?

Neuroimaging (Devinsky & D’Esposito, 2004: p. 52) might be defined as the general term for diagnostic imaging techniques used for “precise anatomical localization of cognitive deficits after brain injury.” In other words, neuroimaging (NI) per se has origins stemming directly from clinical medicine, neurology and neuropsychology. The use of X-rays in the diagnosis of neurological damage or disease perhaps quite rare, unless of course the suspicion arises that a patient may have a related dysfunction in another part of the body (e.g., cancer). A more likely contemporary scenario is that computerized tomography (CT) is useful in the diagnosis of structural lesions (e.g., tumours, major stroke or skull fractures). Magnetic resonance imaging (MRI) provided detailed image resolutions (e.g., 1.5 tesla = 1mm, 4 tesla ≤ 1mm) and does not involve the use of radiation. However, MRIs are very large, noisy and expensive machines. MR angiography and venography (MRA/MRV) imaging is used for the most part to scan major blood vessels into, out of and within the brain (e.g., stenosis, aneurysms or venous sinus thrombosis: see also Barker & Barasi, 2008; ). Single photon emission computed tomography (SPECT) has a lower resolution than MRI and utilised very short half-life isotopes (see below). Positron emission tomography (PET) detects for the emergence of positrons with identifying characteristics dependent on the particular substrate. Again, radioactive isotopes of the kind used in SPECT are required. Last, but by no means least there is functional MRI (fMRI) imaging apparatus. fMRI is a powerful research device which was adapted from MRI technology and records functional changes related to tissue function in successive images (Devinsky & D’Esposito, 2004; Jezzard, Matthews, & Smith, 2001; Kandel et al., 2000; Kwong et al., 1992).

The origins of modern imaging techniques owe much to the efforts of two research physicists (Bloch, 1946; Purcell, 1946) who initially reported their findings relating to nuclear magnetic resonance (NMR) quite independently in 1945 (see also Symms, Jäger, Schmierer, & Yousry, 2004). Both Bloch and Purcell went on to share the 1952 Nobel Prize in Physics: “for their development of new methods for nuclear magnetic precision measurements and discoveries in connection therewith” (Liljestrand, 1953). Notwithstanding, the emergence of stable radiofrequency technologies, and their becoming more widely available by 1945, may be largely attributed to the wartime advancement of defence systems, more specifically, radar.

NMR as a technique of and for diagnostic imaging remained static up to 1971, whereupon Damadian’s (1971) experiments with tissue and tumour relaxation times, under the influence of NMR, might have provided an impetus for other researchers. Investigations of the time into image formations and differing diffraction times across various solids were proving fruitful (e.g., Lauterbur, 1973; Mansfield, 1973). The first human participant in vivo MR images were produced by Lauterbur (1973) working with test tube samples. In the same propitious year, Hounsfield, whilst employed with EMI Ltd., developed what was initially called computerized transverse axial scanning techniques – which later became recognisable as x-ray based computerized tomography (CT). CT was developed by generating images of tissue density made by replacing the traditional x-ray film or plate with crystal detectors and calculating the attenuation of x-rays as they passed through the body (Ambrose, 1973). Cormack and Hounsfield went on to share the 1979 Nobel Prize in Physiology or Medicine: “for the development of computer assisted tomography” (Odelberg, 1980).

Positron Emission Tomography (PET) is an astonishingly complex functional imaging technology. Put rather crudely, PET works by detecting the annihilation of photons by electrons between two large radiation detectors linked to a ‘coincidence circuit’. The impact of two positrons contacting the detectors at precisely the same time is represented graphically by computation. These computations produce a geometric image of the radioactivity of the human body – that is, after the administration of a substance incorporating radioactive atoms with extremely short half-lives (e.g., oxygen-15, nitrogen-13 or carbon-11; see also Raichle, 1983, 1986). PET and its variants (i.e., SPECT/rCBF) may also use several arrays of detectors around the head of the subject permitting many in vivo tomographic anatomical sections (Raichle, 1983).

Ernst (1975) had ventured that MR use frequency and phase encoding – the Fourier Transform NMR and MRI, which is still the platform on which contemporary MRI/fMRI are built. Ernst joined the list of Nobel laureates in 1991, this time in Chemistry, “for his contributions to the development of the methodology of high resolution nuclear magnetic resonance (NMR) spectroscopy” (Frängsmyr, 1992). By 1987, magnetic resonance angioplasty (MRA) extended existing MRI technologies into the realm of real-time cardiac imaging. In 1991, a functional MRI (fMRI) was successfully prototyped, tested on seven subjects and the extraordinary findings published demonstrating neuronal responses to single events to be measured (Jezzard, Matthews, & Smith, 2001; Kwong et al., 1992). Lauterbur and Mansfield were jointly awarded the Nobel Prize in Physiology or Medicine 2003 for their discoveries concerning magnetic resonance imaging.

How does neuroimaging benefit patients and aid professionals in their quest toward providing effective neurological diagnoses and/or treatments?

Neurological study of the cognitive processes reveals that complex functionalities can sometimes be demonstrated as localized to specific areas (e.g.,V1, V2, V4). Never the less, the question of whether function is ever localized or seen as an element of an ensemble property of the nervous system as a whole continues to be an obstinate barrier to our understanding. For Saper, Iverson, & Frankowiak (in Kandel et al., 2000: p. 365) this problematic appears as a “dialectical issue” in that, as they themselves point to, no single component of a mechanism functions identically in isolation as it might when in concert with the other components that compose the whole mechanism. In other words, it is improbable that the neural basis of any cognitive function (e.g., sight, thought, language or memory) will be understood to be autonomous.

One of the immediate benefits offered by the relatively recent establishment of functional neuroimaging, therefore, might be suggested to come from the actuality of anatomical detailing of brain injury in living patients (e.g. haemorrhaging). Another clear benefit to the patient is the removal of any previous (i.e., PET/SPECT/cCBF) requirement for an injection of radioisotopes – MRI/fMRI, for instance, is a non-invasive technique. That said, there are occasions when PET might be of superior benefit over MRI/fMRI; for instance, as Devinsky & D’Esposito (2004: p. 55) have pointed out, clear imaging of the orbitofrontal cortex and the anterior or inferior temporal lobe are problematic “because of as susceptibility to artifact near the interface of the brain and sinuses.” One might also cite the example of testing auditory processes using fMRI quite unmanageable due to the excessive noise generated by the gradient coils.

The above are quiet general benefits that, whilst centred on PET and MRI/fMRI, offer substantial generalized benefits to patients and professional clinicians in their daily lives. However, as a final example of benefits to patients and professionals providing effective neurological diagnoses and/or treatments, one might attend to a quite specific problem with a widespread effect – depression. Recent research (Weissman & Peterson, 2009) suggests that a large-scale imaging-study of ‘depression’ appears compatible with the proposal that a ‘thinning’ (28% in thickness) of the right cerebral hemisphere may be associated with those at a significantly higher risk of suffering with depressive disorders. These data are similar to those already known for Alzheimer’s and schizophrenia. In their study Weissman & Peterson compared the thickness of the cortex by neuroimaging the brains of one hundred and thirty-one (131) participants, aged six (6) to fifty-four (54) years, with and without a genetic traceability of depression. It was also noteworthy that these structural ‘thinning’ differences were found in the direct biological offspring of depressed subjects, but were not found in the biological offspring of those who were not depressed. One might reasonably ask therefore if such a finding, with such influence over so many people (1 in 5 across full lifetime), could possibly have become known had it not been for neuroimaging.

What are some of the implications for patients in a future where neuroimaging might reasonably be assumed as situated at the heart of neurological and neuropsychological investigation?

Clinicians have accepted the role of neuroimaging in diagnosis and therapy. The favourable reception of minimally invasive procedures resulted in the recognition of the feasibility of image-guided approaches. Although radiology has now combined neuroimaging with various novel therapeutic methods, the full use of advanced neuroimaging technology has not yet been realized. One might say that the current trend appears to be the evolution of integrated therapy delivery systems in which advanced neuroimaging modalities are closely linked with high-performance computerization. It is clear that the neurosurgeons operating theatre of the future will accommodate various instruments, tools and devices, each of which attached to some form of neuroimaging system and controlled perhaps by object-oriented user interfaces.

Reflections in conclusion

The present discussion looked at three fundamental questions concerned with neuroimaging and sought to address them: What is neuroimaging? How does neuroimaging benefit patients and aid professionals in their quest toward providing effective neurological diagnoses and/or treatments? Furthermore, what are some of the implications for patients in a future where neuroimaging might reasonably be assumed as situated at the heart of neurological and neuropsychological investigation? It is perhaps a constant concern to clinicians that the constraint within the UK public health – specifically with regard to neurological injury, dysfunctions and cognitive deficits – appears once again not to lie with the lack of professionalism or expertise but rather with the economic model of providing health care.

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