WEBVTT 1 00:00:05.133 --> 00:00:10.732 Nuclear Medicine groups together all of the medical applications that use radioelements 2 00:00:10.733 --> 00:00:13.699 that is radioactive sources. 3 00:00:13.700 --> 00:00:18.299 Scintigraphy is an imaging technique that involves tracking the distribution 4 00:00:18.300 --> 00:00:19.765 in the patient’s body 5 00:00:19.766 --> 00:00:24.899 of radioactive elements that have been introduced in very small quantities. 6 00:00:24.900 --> 00:00:27.899 To understand how this works, let’s review some Physics: 7 00:00:28.833 --> 00:00:32.799 The majority of the chemical elements found in Nature are stable. 8 00:00:32.800 --> 00:00:36.899 But certain elements called “radioactive”, are unstable. 9 00:00:36.900 --> 00:00:40.299 That is, with the passage of time and in a random manner 10 00:00:40.300 --> 00:00:43.299 they disintegrate in order to transform themselves 11 00:00:43.300 --> 00:00:46.999 into another atom with more stable properties. 12 00:00:47.000 --> 00:00:49.832 Of all the different kinds of known disintegrations 13 00:00:49.833 --> 00:00:53.099 they all have the release of energy in common. 14 00:00:53.100 --> 00:00:57.932 In scintigraphy, the one that emits gamma radiation is the most interesting 15 00:00:57.933 --> 00:01:01.632 because gamma photons can be detected with a gamma camera. 16 00:01:03.433 --> 00:01:07.765 More than the slow progress of the radioactive element in the human body 17 00:01:07.766 --> 00:01:12.432 it is its fixation inside certain tissues that we seek to detect. 18 00:01:12.433 --> 00:01:16.265 Thus the activities of certain organs or pathological processes 19 00:01:16.266 --> 00:01:19.832 can be explored in a very targeted manner. 20 00:01:19.833 --> 00:01:23.399 It is for this reason that we speak of functional imagery 21 00:01:23.400 --> 00:01:30.165 as opposed to an atomical imagery which shows the contours and densities of organs. 22 00:01:30.166 --> 00:01:33.699 The radioactive element is chosen according to its affinity 23 00:01:33.700 --> 00:01:36.199 for the organ that is to be explored 24 00:01:36.200 --> 00:01:40.799 We see here, for example, the fixation of a tracer in the lungs 25 00:01:40.800 --> 00:01:44.732 which enables us to evaluate pulmonary irrigation. 26 00:01:48.433 --> 00:01:52.399 The examination begins well before the patient is brought in 27 00:01:52.400 --> 00:01:56.199 with the early morning delivery, or the fabrication on site 28 00:01:56.200 --> 00:02:00.132 of different radiotracers in a radiopharmacy. 29 00:02:00.133 --> 00:02:03.432 Let’s consider bone scintigraphy as an example. 30 00:02:03.433 --> 00:02:09.699 The radiopharmacist will create a bone tracer by tagging a medication (diphosphonate) 31 00:02:09.700 --> 00:02:14.765 with a radioactive element (Technetium 99m). 32 00:02:14.766 --> 00:02:18.999 The handling of medications, and even more so, radioactive ones 33 00:02:19.000 --> 00:02:24.632 requires a very strict protocol and is carried out in a protected environment. 34 00:02:24.633 --> 00:02:29.399 The radioelements are always stored and transported in lead containers. 35 00:02:29.400 --> 00:02:33.199 When the final product is ready to be administered to the patient 36 00:02:33.200 --> 00:02:39.132 it is put in a syringe, itself inside a tungsten syringe protector. 37 00:02:39.133 --> 00:02:42.665 Because the radioactivity being handled is very weak 38 00:02:42.666 --> 00:02:46.732 all of these measures serve primarily to protect the personnel 39 00:02:46.733 --> 00:02:49.765 who are subject to the most exposure. 40 00:02:49.766 --> 00:02:54.165 The radiotracer is then administered to the patient by injection. 41 00:02:54.166 --> 00:02:58.365 It takes time for it to diffuse and be captured by the targeted organ 42 00:02:58.366 --> 00:03:01.032 in this case, the skeleton. 43 00:03:01.033 --> 00:03:07.265 For the next step, the patient is placed on an examination table under a gamma camera 44 00:03:07.266 --> 00:03:11.099 which will measure the radiation emitted by the patient. 45 00:03:11.100 --> 00:03:13.399 By progressively moving the table 46 00:03:13.400 --> 00:03:19.199 one can achieve a full body scan in order to obtain an image of the skeleton. 47 00:03:19.200 --> 00:03:23.865 The heads of the gamma cameras are mobile and, for certain examinations 48 00:03:23.866 --> 00:03:28.732 they can be made to turn around the patient to provide images in sections 49 00:03:28.733 --> 00:03:31.899 this is known as tomoscintigraphy. 50 00:03:31.900 --> 00:03:37.999 This is the case for this heart examination, carried out at rest or after a stress test. 51 00:03:42.000 --> 00:03:46.665 The appearance of the images obtained depends on the organ being studied. 52 00:03:46.666 --> 00:03:48.365 With the thyroid, for example 53 00:03:48.366 --> 00:03:52.032 which is an endocrine gland located at the base of the neck 54 00:03:52.033 --> 00:03:58.899 one will inject the patient with a radioactive isotope of iodine (iodine 123) 55 00:03:58.900 --> 00:04:01.132 which is used in hormone production. 56 00:04:01.133 --> 00:04:07.132 The static image, which is taken 2 hours after the injection, gives us, on one hand 57 00:04:07.133 --> 00:04:12.099 information about the gland’s morphology, but above all about its functioning. 58 00:04:12.100 --> 00:04:15.765 In this photograph, thyroid activity is normal. 59 00:04:15.766 --> 00:04:19.865 On this one, by contrast, we see that the gland is larger 60 00:04:19.866 --> 00:04:26.232 and displays a diffuse hyperfixation related to overactivity on the part of the gland 61 00:04:26.233 --> 00:04:29.799 a hormonal disorder named hyperthyroidism. 62 00:04:29.800 --> 00:04:34.332 In the opposite case, the very weak fixation of iodine in this photograph 63 00:04:34.333 --> 00:04:40.365 taken with the same exposure time, indicates a slowed down thyroid function. 64 00:04:40.366 --> 00:04:42.532 This is hypothyroidism. 65 00:04:42.533 --> 00:04:45.665 On these two other photographs one can see abnormal 66 00:04:45.666 --> 00:04:50.865 rounded structures in the interior of the gland. These are nodules. 67 00:04:50.866 --> 00:04:54.332 On the left we have hyperfixing “hot nodules” 68 00:04:54.333 --> 00:04:58.465 and on the right the hypofixing “cold nodules”. 69 00:04:58.466 --> 00:05:04.132 In the case of bone scintigraphy, the tracer used is one with an affinity for bone. 70 00:05:04.133 --> 00:05:07.165 Here is what we see in a healthy subject. 71 00:05:07.166 --> 00:05:12.165 Cancer cells have higher level of metabolic activity than healthy ones 72 00:05:12.166 --> 00:05:16.899 so the pockets of hyperfixation reveal the presence of metastases. 73 00:05:16.900 --> 00:05:20.932 Here is a final example, myocardial scintigraphy. 74 00:05:20.933 --> 00:05:26.199 After computer analysis, images in section are obtained with colored zones 75 00:05:26.200 --> 00:05:29.765 that indicate good irrigation of the myocardium. 76 00:05:29.766 --> 00:05:32.899 The same observation made after a stress test 77 00:05:32.900 --> 00:05:39.165 reveals an area that has not taken up the tracer (in this case thallium 201). 78 00:05:39.166 --> 00:05:43.132 Thus an ischemia is diagnosed, that is to say 79 00:05:43.133 --> 00:05:48.165 poor oxygenation resulting from a coronary stenosis. 80 00:05:49.833 --> 00:05:58.865 PET Scan. The letters “P” “E” “T” are the acronym for Positron Emission Tomography. 81 00:05:58.866 --> 00:06:04.232 The principle is the same in that we inject a radioactive tracer into the patient’s body 82 00:06:04.233 --> 00:06:09.799 but here it is a beta+ disintegration that will be detected indirectly. 83 00:06:09.800 --> 00:06:15.265 If we take this normal image, primarily the brain and the myocardium can be seen 84 00:06:15.266 --> 00:06:20.199 which are heavy consumers of glucose, as well as the urinary passages 85 00:06:20.200 --> 00:06:23.265 indicating the elimination of the tracer. 86 00:06:23.266 --> 00:06:27.299 In these other images, pockets of cancer can be detected 87 00:06:27.300 --> 00:06:33.532 because cancer cells require a lot of energy in relation to their activity of proliferation. 88 00:06:33.533 --> 00:06:35.899 The images obtained with this technique 89 00:06:35.900 --> 00:06:40.532 can be superimposed over the tomodensitometric image of the same region 90 00:06:40.533 --> 00:06:44.899 provided by a CT-scan linked to the apparatus. 91 00:06:44.900 --> 00:06:51.032 An anatomic image: Scan and a functional image: PET are thus combined. 92 00:06:51.033 --> 00:06:54.865 Scintigraphy helps us to visualize the functioning of organs 93 00:06:54.866 --> 00:06:58.332 in a simple and only slightly invasive manner. 94 00:06:58.333 --> 00:07:02.599 For a patient stricken with a neurodegenerative disease, for example 95 00:07:02.600 --> 00:07:07.099 MRI or a CT-scan only show normal structure 96 00:07:07.100 --> 00:07:12.299 whereas scintigraphy reveals those areas of the brain that are no longer functioning. 97 00:07:12.300 --> 00:07:15.665 The use of very weak doses of radioactive elements 98 00:07:15.666 --> 00:07:18.832 has not shown any undesirable effects. 99 00:07:18.833 --> 00:07:23.965 As a precautionary measure this examination is always contraindicated 100 00:07:23.966 --> 00:07:27.132 for pregnant or nursing women. 101 00:07:27.133 --> 00:07:30.399 The personnel are equipped with dosimeters (and rings) 102 00:07:30.400 --> 00:07:34.399 in order to ensure that their exposure to radiation remains within the norms.