Pioneers; Hounsfield & Cormack

Godfrey Hounsfield (1919-2004) was a British electrical engineer who developed computed tomography (CT). 

In 1949, Hounsfield began working at EMI, Ltd where he researched guided weapon systems and radar.  At EMI, he became interested in computers and in 1958, he helped in the design of the first computer system in Great Britain. Shortly afterwork he started work on CT scanner.   

Hounsfield came up with the idea that one could determine what was inside a box by taking x-ray readings at multiple angles around an object.  He then built a computer that could take input from x-rays at various angles to create an image of the object in slices.  Applying this idea to the medical field led him to what is known today as computed tomography. The scale of units he used (HD), running from -1000 HD for air, 0 HD for water, and +1000 HD for cortical bone are the quantitive measures used in obtaining, depicting and evaluating a CT scan.

At that time, Hounsfield was not aware of the work and the two papers Allan Cormack (1924-1988) had published in 1956 on the theoretical basis of such a device when he worked at the University of Cape Town and Groote Schuur Hospital.

Hounsfield built a prototype head CT scanner and tested it first on a cadaver's brain and soon after on a cow's brain and finally on himself.  On October 1st 1971, CT scanning was introduced in medical practice with a brain scan performed on a patient and in 1975 Hounsfield built a whole body scanner. 

In 1979, Hounsfield and Cormack received the Nobel Prize in Physiology and Medicine.  Both received numerous awards in addition to the Nobel and Hounsfield was also knighted in 1981.

The above post is dedicated to Dr John Andreou and Professor A Gouliamos  prominent Greek radiologists whose expertise in computed tomography contributed in establishing it as a pre-eminent diagnostic method in Greece.  in addition to being a good colleagues I also thank them for being good friends to me for the past 50 years.

CT Contrast Shortage is Affecting Radiology

 A paper published in Radiology discusses the current shortage of CT contrast which is prompting Radiology departments to make dramatic changes in imaging protocols and patient triage.

Low Radiation Dose CT Leads to Inferior Diagnoses

Jensen et al reported in Radiology that CT evaluation of colorectal liver metastases was not as accurate after reducing the radiation exposure by more than 50 percent. 

Their study included 52 patients with biopsy-proven colorectal cancer liver metastases and few benign lesions as well.  Each patient underwent two CT scans-a standard radiation dose (SD) contrast CT and a reduced radiation dose (RD) CT scan- during the same breast hold.

Reduced dose CT resulted in a mean dose reduction of 54% compared with standard dose. Of the 260 lesions, 233 were metastatic and 27 benign, 212 were detected with RD CT, whereas 252 were detected with SD CT.   Mean qualitative scores ranked SD images as higher quality versus RD series images.

The authors concluded that CT evaluation of colorectal liver metastases is compromised with reduced radiation dose, and the use of iterative reconstructions could not maintain observer performance.

CT Angiography is Accurate in Diagnosis of Small Cerebral Aneurysms

A study published by Yang et al in Radiology assessed the accuracy of computed tomographic (CT) angiography for diagnosis of cerebral aneurysms 5 mm or smaller.

A total of 1366 patients who underwent cerebral CT angiography followed by DSA were included in the study.

Of 1366 patients in their study, 579 patients had 711 small aneurysms at DSA. By using DSA as the reference standard, the respective sensitivity, specificity, and accuracy of CT angiography was analyzed for two readers.  The sensitivity of CT angiography was lower for detection of aneurysms smaller than 3 mm that had not ruptured compared with aneurysms that were 3–5 mm and had ruptured (P < .001). No difference existed for the sensitivities of CT angiography for diagnosis of aneurysms in the anterior versus posterior circulation (P > .0167). Excellent or good inter-reader agreement was found for detection of intracranial aneurysms on a per-patient (κ = 0.982) and per-aneurysm (κ = 0.748) basis.

The authors concluded that CT angiography has high accuracy for detection of small cerebral aneurysms.

CMS approves CT Lung Cancer Screening

The Centers for Medicare and MedicaidServices on February 6, 2015 issued its final decision approving Medicare coverage for lung cancer screening by low-dose CT.  Medicare will cover annual screenings for beneficiaries aged 55-77 who are current smokers or who quit in the last 15 years, and who have a history of at least 30 “pack years.”   According to the American Cancer Society, lung cancer kills nearly 158,000 patients a year.

Incidental Findings on Non-Enhanced CT on Patients with Renal Colic

Samim et al in their article published by the Journal of AmericanCollege of Radiology report the prevalence and types of incidental findings on non-enhanced computed tomograms performed on patients with renal colic in the Emergency Department.

They reviewed 5,383 consecutive reports retrospectively of non-enhanced CT performed on adult patients using renal colic protocol at 2 emergency departments over a 5.5-year period. Incidental findings were defined as those unrelated to symptoms and were categorized as “important” if follow-up was recommended based on recently published consensus recommendations.

Important incidental findings (IF) were identified in 12.7% of scans. Prevalence of important incidental findings increased with age: important IF in individuals age >80 years were 4 times more common than for those aged 18-30 years: 28.9% versus 6.9%, respectively, (P ≤ .05). Women had a higher prevalence of important IF compared with men: 13.4% versus 11.9%, but the difference was not statically significant (P = .09). There was substantial inter-rater agreement (kappa ≥ 0.69) regarding presence and classification of important incidental findings using published guidelines.

The authors concluded that important incidental findings occurred in 12.7% of non-enhanced CT scans performed for suspected renal colic in the emergency department and are more common in older individuals.

CT identifies TIA patients at high risk for Stroke

Wasserman et al in a study published by the journal Stroke report that computed tomography (CT) findings can predict subsequent stroke on patients with transient ischemic attacks (TIA).

Their multicenter prospective cohort study enrolled a total of 2028 patients; 814 of who had ischemic changes on CT and were patients with a clinical diagnosis of an transient ischemic attack or non-disabling stroke and had CT scanning within 24 hours of the event. Primary outcome was subsequent stroke within 90 days. Secondary outcomes were stroke at ≤2 or >2 days. CT findings were classified as acute or chronic ischemia present or absent and or microangiopathy.

The stroke rate was 3.4% at 90 days and 1.5% at ≤2 days. Stroke risk was greater if baseline CT showed acute ischemia alone (10.6%; P=0.002), it was higher in patients with CT findings of acute and chronic ischemia (17.4%; P=0.007), and in those with acute ischemia and microangiopathy (17.6%; P=0.019), and the highest when CT findings of all three acute, chronic ischemia and microangiopathy were present (25.0%; P=0.029).

They concluded that patients with transient ischemic attack/non-disabling stroke, subtle CT findings of acute ischemia alone or acute ischemia with chronic ischemia or microangiopathy were associated with increased subsequent stroke risk between 10-25% within 90 days. 

Malpractice Reform does not Affect ED Utilization

Waxman et al report in NEJM their findings regarding the effect legal reform had in the practice of medicine, in three states, Texas, Georgia, and South Carolina, which between 2003 and 2005, enacted legislation that changed the malpractice standard for emergency care to gross negligence.  

Using a 5% random sample of Medicare fee-for-service beneficiaries, they identified all emergency department visits to hospitals in the three reform states and in neighboring (control) states from 1997 through 2011. They compared patient-level outcomes, before and after legislation, in reform states and control states. Outcomes were policy-attributable changes in the use of computed tomography (CT) or magnetic resonance imaging (MRI), per-visit emergency department charges, and the rate of hospital admissions.

For eight of the nine states–outcome combinations tested, they found no reduction in the rates of CT or MRI utilization or hospital admission in any of the three reform states and no reduction in charges in Texas or South Carolina. In Georgia, reform was associated with a 3.6% reduction in per-visit emergency department charges.

They conclude that legislation that substantially changed the malpractice standard for emergency physicians in three states had little effect on the intensity of practice, as measured by imaging rates, average charges, or hospital admission rates.

Ambulance-Based Thrombolysis in Acute Ischemic Stroke

Ebinger et al report in JAMA the result a specialized ambulance has in the initiation of treatment in patients with acute ischemic strokes.

Their study was conducted in Berlin, Germany over a 21 months period between 2011 and 2013 when a Stroke Emergency Mobile (STEMO) unit was dispatched every other week to care of patients with strokes. The STEMO was an ambulance equipped with a CT scanner, point-of-care laboratory, with telemedicine connection, a physician, a paramedic and an x-ray technician. Thrombolysis was started before transport to hospital if ischemic stroke was confirmed and contraindications excluded.  During the study period 6182 adult patients were included.

There was a reduction of 25-minutes in alarm-to-treatment times for STEMO compared to control weeks.  The 25-minute reduction was due to faster alarm-to-imaging and imaging-to-treatment intervals. Fifty eight percent of patients were treated within 90 minutes of onset versus 37% in the control.  The intervention also resulted in 33% patients treated with tPA versus 21% in the control.  STEMO deployment incurred no increased risk for intra-cerebral hemorrhage (7/200 vs 22/323); or 7-day mortality (9/199 versus 15/323).

A prior study by Walter et al¹ who also used a mobile stroke unit and treated patients with acute ischemic stroke with tPA safely within 70 to 80 minutes.

The authors conclude the use of ambulance-based thrombolysis resulted in decreased time to treatment without an increase in adverse events. 

1.  Walter S, Kostopoulos P,  Haass A et al. Diagnosis and treatment of patients with stroke in a mobile unit versus hospital: a randomized study controlled trial Lancet Neurol. 2012;11(5):397-404