6.4 Taking the image

Activity 12

Now watch this video clip of a patients lungs being imaged, called a VQ (ventilation quotient) scan. What are the two different types of acquisitions used called? What radioactive substance is used for each acquisition, and why
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6.3.2 Crystal

Almost all modern gamma cameras use (thallium-doped) sodium iodide (NaI) as the scintillation crystal. A gamma photon interacts with the crystal to produce many photons of visible light.

Sodium iodide is hygroscopic so cannot be left exposed to the air. The front surface is coated with a low atomic number metal that allows the gamma photons to pass through. The rear surface is covered with a transparent coating so that the visible photons can pass through to the photomultiplier tubes.
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6.3.1 Collimator

Without a collimator, gamma rays from all directions would be collected by the crystal and no useful image could be obtained. Gamma rays cannot be focused by a lens but a collimator consisting of a series of holes in a lead plate can be used to select the direction of the rays falling on the crystal. Most collimators in use today are parallel hole collimators. A parallel hole collimator is shown schematically in Author(s): The Open University

6.2 Producing the radioactive substance (elution)

In the radiopharmacy Tc-99m is produced in a generator.

Mo-99, a product of the fission of uranium, is isolated from a nuclear reactor and absorbed on to an alumina column in the generator. When a saline solution is passed over the column, ion exchange results in the production of sodium pertechnetate. This can then be chemically manipulated to form a variety of compounds. The removal of the technetium by the passage of saline is known as elution.

Conveniently, the optimum interva
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5 Ultrasound

Ultrasound imaging uses acoustic waves, rather than ionizing radiation, to form an image. The principle is rather like radar; a pulse of ultrasound (1–15 MHz) is sent out from the transducer and reflected from tissue boundaries. Measurement of the time taken for the pulse to return allows the distance to the reflecting boundary to be calculated.

The important parameter determining the amount of reflection is known as the acoustic impedance (Z) of the tissue and is the product o
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2.2 The kinkajou

LoM describes this tree dweller as a relative of the raccoon. It belongs to the order Carnivora and is one member of a family generally referred to as procyonids [p. 170], or more commonly the raccoon family. You'll be aware that some members of this family – for example, coatis [p. 174] – are omnivores. As you'll see in the video sequence below, coatis are more typically found in the undergrowth and leaf litter, rather than high up in the trees. (If you need to remind yourself of the lif
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7 The threat of extinction

DA ends his book by writing eloquently of the dangers of extinction faced by mammals, from habitat loss as we exploit our environment to produce more and more food, for our growing population. However bleak the picture, there is still time and opportunity to save mammal species from extinction. Although bison in the USA and Canada were reduced to barely 1000 individuals in 1900, their numbers have now risen to well over 150 000 thanks to the efforts of First Nation indigenous peoples, and ran
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4 Who were the ancestors of Homo?

Fossil evidence supports Darwin's view that humans and apes evolved from an ape-like ancestor and, furthermore, suggests that the ape line diverged from the Homo line at least five million years ago (Figure 1). From our current knowledge of the fossils available to us, the evolutionary tree in
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5 Miss Piggy

As the earliest mammals – the insectivores – were specialists, it follows that the omnivore lifestyle must have arisen at some later stage in a group or groups of non-omnivores. In fact, both seed eating and leaf eating arose before omnivory. Twenty million years ago, Dinohyus was undoubtedly a ‘specialist’ omnivore.

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4.2 Other members of the bear family

Other omnivorous species of bear include the Asian black bear, the North American black bear and the Andean spectacled bear. Although polar bears spend their winters hunting seals out on the Arctic sea-ice, they have to come ashore when the ice melts in spring and find other sources of food.

Activity 2
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4.1 The grizzly bear

There are three activities in Section 4, asking you to summarise information in the form of lists. In the first two, the answers are given but in the third, about the diet of the giant panda, they are not. You are asked to tick off the points in your list as you read on through the section. As you gain more stu
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2.2 Energy flow in ecosystems

You are about to meet some very large numbers, expressed in scientific notation, and some new units. The new units are those that are used to measure the amount of solar energy received by a part of the Earth's surface. Since plants are dependent on light for photosynthesis, the amount of plant material that ca
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1 The omnivores

As you work through this unit you will come across boxes, like this one, which give you advice about the study skills that you will be developing as you progress through the unit. To avoid breaking up the flow of the text, they will usually appear at the start or end of the sections.

As well as the un
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Acknowledgements

Except for third party materials and otherwise stated (see terms and conditions), this content is made available under a Creative Commons Attribution-NonCommercial-ShareAlike 2.0 Licence

Grateful acknowledgement is made to the following sources for permission to reproduce material in this unit:

The content acknowl
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Claws

Claws are important for grabbing prey. They must be kept sharp and trees (or chair legs, as domestic cat owners can confirm) are used as scratching posts. In all cats other than the cheetah, the claws can be retracted into a sheath within the footpad, preventing rapid wear.


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3.1 Speed and endurance

The first question in this section is a mathematical one, in which you are asked to convert from one set of units to another. If you have been following the advice in previous units in this series, you will be reading km h−1 as kilometres per hour and you will probably already think of m.p.h. as mi
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Learning outcomes

By the end of this unit you should be able to:

  • describe some of the characteristic features of carnivores;

  • outline the dentition of carnivores and its link with diet;

  • outline some of the behavioural and sensory characteristics of carnivores, with examples;

  • explain, with examples, the roles that vision and smell play in the lives of carnivores;

  • explain the variety of ways in which carnivores assemble in groups;

  • <
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Introduction

In this unit, we will examine the biology of the impressive meat eaters (e.g. wolves, lions and cheetahs), focusing in part on the biological ‘equipment’ – slashing and gripping teeth, for example – and on the less obvious behavioural characteristics that have contributed to the undoubted success of these fearsome hunters. Many of the meat eaters live and hunt in groups, which raises intriguing questions about the advantages of group living and the types of social behaviour between in
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10 Living in herds

Wildebeest are only one of the species of plant predator that live in herds. Many others do too.

Activity 7

Watch the the TV programme from 30.48–47.32 and read LoM p. 109. Identify and write down (a) a couple of advantages and
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5.1.1 Starting points

We begin by making some simplifying assumptions about the electric field. This is legitimate because we are not looking for the most general solution to Maxwell's equations, but only for special solutions that exhibit wave-like behaviour. We will ultimately check that our solutions for the fields satisfy all of Maxwell's equations, and hence obtain retrospective support for our initial assumptions.

If you drop a pebble in a pond, waves spread out in all directions on the surface. Many e
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